1891 lines
79 KiB
Rust
1891 lines
79 KiB
Rust
//! # Type Coercion
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//!
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//! Under certain circumstances we will coerce from one type to another,
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//! for example by auto-borrowing. This occurs in situations where the
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//! compiler has a firm 'expected type' that was supplied from the user,
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//! and where the actual type is similar to that expected type in purpose
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//! but not in representation (so actual subtyping is inappropriate).
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//!
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//! ## Reborrowing
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//!
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//! Note that if we are expecting a reference, we will *reborrow*
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//! even if the argument provided was already a reference. This is
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//! useful for freezing mut things (that is, when the expected type is &T
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//! but you have &mut T) and also for avoiding the linearity
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//! of mut things (when the expected is &mut T and you have &mut T). See
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//! the various `src/test/ui/coerce/*.rs` tests for
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//! examples of where this is useful.
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//!
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//! ## Subtle note
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//!
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//! When inferring the generic arguments of functions, the argument
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//! order is relevant, which can lead to the following edge case:
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//!
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//! ```ignore (illustrative)
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//! fn foo<T>(a: T, b: T) {
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//! // ...
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//! }
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//!
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//! foo(&7i32, &mut 7i32);
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//! // This compiles, as we first infer `T` to be `&i32`,
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//! // and then coerce `&mut 7i32` to `&7i32`.
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//!
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//! foo(&mut 7i32, &7i32);
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//! // This does not compile, as we first infer `T` to be `&mut i32`
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//! // and are then unable to coerce `&7i32` to `&mut i32`.
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//! ```
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use crate::astconv::AstConv;
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use crate::check::FnCtxt;
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use rustc_errors::{
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struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
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};
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_hir::intravisit::{self, Visitor};
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use rustc_hir::Expr;
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use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use rustc_infer::infer::{Coercion, InferOk, InferResult};
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use rustc_infer::traits::{Obligation, TraitEngine, TraitEngineExt};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty::adjustment::{
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Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, PointerCast,
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};
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use rustc_middle::ty::error::TypeError;
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use rustc_middle::ty::relate::RelateResult;
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use rustc_middle::ty::subst::SubstsRef;
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use rustc_middle::ty::visit::TypeVisitable;
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use rustc_middle::ty::{self, ToPredicate, Ty, TypeAndMut};
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use rustc_session::parse::feature_err;
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use rustc_span::symbol::sym;
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use rustc_span::{self, BytePos, DesugaringKind, Span};
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use rustc_target::spec::abi::Abi;
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use rustc_trait_selection::infer::InferCtxtExt as _;
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use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
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use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
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use smallvec::{smallvec, SmallVec};
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use std::ops::Deref;
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struct Coerce<'a, 'tcx> {
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fcx: &'a FnCtxt<'a, 'tcx>,
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cause: ObligationCause<'tcx>,
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use_lub: bool,
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/// Determines whether or not allow_two_phase_borrow is set on any
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/// autoref adjustments we create while coercing. We don't want to
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/// allow deref coercions to create two-phase borrows, at least initially,
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/// but we do need two-phase borrows for function argument reborrows.
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/// See #47489 and #48598
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/// See docs on the "AllowTwoPhase" type for a more detailed discussion
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allow_two_phase: AllowTwoPhase,
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}
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impl<'a, 'tcx> Deref for Coerce<'a, 'tcx> {
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type Target = FnCtxt<'a, 'tcx>;
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fn deref(&self) -> &Self::Target {
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&self.fcx
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}
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}
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type CoerceResult<'tcx> = InferResult<'tcx, (Vec<Adjustment<'tcx>>, Ty<'tcx>)>;
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struct CollectRetsVisitor<'tcx> {
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ret_exprs: Vec<&'tcx hir::Expr<'tcx>>,
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}
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impl<'tcx> Visitor<'tcx> for CollectRetsVisitor<'tcx> {
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fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
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if let hir::ExprKind::Ret(_) = expr.kind {
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self.ret_exprs.push(expr);
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}
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intravisit::walk_expr(self, expr);
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}
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}
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/// Coercing a mutable reference to an immutable works, while
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/// coercing `&T` to `&mut T` should be forbidden.
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fn coerce_mutbls<'tcx>(
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from_mutbl: hir::Mutability,
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to_mutbl: hir::Mutability,
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) -> RelateResult<'tcx, ()> {
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match (from_mutbl, to_mutbl) {
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(hir::Mutability::Mut, hir::Mutability::Mut | hir::Mutability::Not)
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| (hir::Mutability::Not, hir::Mutability::Not) => Ok(()),
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(hir::Mutability::Not, hir::Mutability::Mut) => Err(TypeError::Mutability),
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}
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}
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/// Do not require any adjustments, i.e. coerce `x -> x`.
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fn identity(_: Ty<'_>) -> Vec<Adjustment<'_>> {
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vec![]
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}
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fn simple<'tcx>(kind: Adjust<'tcx>) -> impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> {
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move |target| vec![Adjustment { kind, target }]
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}
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/// This always returns `Ok(...)`.
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fn success<'tcx>(
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adj: Vec<Adjustment<'tcx>>,
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target: Ty<'tcx>,
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obligations: traits::PredicateObligations<'tcx>,
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) -> CoerceResult<'tcx> {
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Ok(InferOk { value: (adj, target), obligations })
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}
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impl<'f, 'tcx> Coerce<'f, 'tcx> {
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fn new(
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fcx: &'f FnCtxt<'f, 'tcx>,
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cause: ObligationCause<'tcx>,
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allow_two_phase: AllowTwoPhase,
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) -> Self {
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Coerce { fcx, cause, allow_two_phase, use_lub: false }
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}
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fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
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debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub);
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self.commit_if_ok(|_| {
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if self.use_lub {
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self.at(&self.cause, self.fcx.param_env).lub(b, a)
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} else {
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self.at(&self.cause, self.fcx.param_env)
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.sup(b, a)
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.map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
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}
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})
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}
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/// Unify two types (using sub or lub) and produce a specific coercion.
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fn unify_and<F>(&self, a: Ty<'tcx>, b: Ty<'tcx>, f: F) -> CoerceResult<'tcx>
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where
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F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
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{
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self.unify(a, b)
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.and_then(|InferOk { value: ty, obligations }| success(f(ty), ty, obligations))
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}
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#[instrument(skip(self))]
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fn coerce(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
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// First, remove any resolved type variables (at the top level, at least):
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let a = self.shallow_resolve(a);
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let b = self.shallow_resolve(b);
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debug!("Coerce.tys({:?} => {:?})", a, b);
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// Just ignore error types.
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if a.references_error() || b.references_error() {
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return success(vec![], self.fcx.tcx.ty_error(), vec![]);
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}
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// Coercing from `!` to any type is allowed:
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if a.is_never() {
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return success(simple(Adjust::NeverToAny)(b), b, vec![]);
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}
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// Coercing *from* an unresolved inference variable means that
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// we have no information about the source type. This will always
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// ultimately fall back to some form of subtyping.
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if a.is_ty_var() {
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return self.coerce_from_inference_variable(a, b, identity);
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}
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// Consider coercing the subtype to a DST
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//
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// NOTE: this is wrapped in a `commit_if_ok` because it creates
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// a "spurious" type variable, and we don't want to have that
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// type variable in memory if the coercion fails.
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let unsize = self.commit_if_ok(|_| self.coerce_unsized(a, b));
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match unsize {
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Ok(_) => {
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debug!("coerce: unsize successful");
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return unsize;
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}
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Err(TypeError::ObjectUnsafeCoercion(did)) => {
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debug!("coerce: unsize not object safe");
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return Err(TypeError::ObjectUnsafeCoercion(did));
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}
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Err(error) => {
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debug!(?error, "coerce: unsize failed");
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}
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}
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// Examine the supertype and consider auto-borrowing.
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match *b.kind() {
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ty::RawPtr(mt_b) => {
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return self.coerce_unsafe_ptr(a, b, mt_b.mutbl);
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}
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ty::Ref(r_b, _, mutbl_b) => {
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return self.coerce_borrowed_pointer(a, b, r_b, mutbl_b);
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}
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_ => {}
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}
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match *a.kind() {
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ty::FnDef(..) => {
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// Function items are coercible to any closure
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// type; function pointers are not (that would
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// require double indirection).
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// Additionally, we permit coercion of function
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// items to drop the unsafe qualifier.
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self.coerce_from_fn_item(a, b)
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}
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ty::FnPtr(a_f) => {
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// We permit coercion of fn pointers to drop the
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// unsafe qualifier.
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self.coerce_from_fn_pointer(a, a_f, b)
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}
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ty::Closure(closure_def_id_a, substs_a) => {
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// Non-capturing closures are coercible to
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// function pointers or unsafe function pointers.
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// It cannot convert closures that require unsafe.
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self.coerce_closure_to_fn(a, closure_def_id_a, substs_a, b)
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}
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_ => {
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// Otherwise, just use unification rules.
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self.unify_and(a, b, identity)
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}
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}
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}
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/// Coercing *from* an inference variable. In this case, we have no information
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/// about the source type, so we can't really do a true coercion and we always
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/// fall back to subtyping (`unify_and`).
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fn coerce_from_inference_variable(
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&self,
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a: Ty<'tcx>,
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b: Ty<'tcx>,
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make_adjustments: impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
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) -> CoerceResult<'tcx> {
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debug!("coerce_from_inference_variable(a={:?}, b={:?})", a, b);
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assert!(a.is_ty_var() && self.shallow_resolve(a) == a);
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assert!(self.shallow_resolve(b) == b);
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if b.is_ty_var() {
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// Two unresolved type variables: create a `Coerce` predicate.
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let target_ty = if self.use_lub {
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self.next_ty_var(TypeVariableOrigin {
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kind: TypeVariableOriginKind::LatticeVariable,
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span: self.cause.span,
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})
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} else {
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b
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};
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let mut obligations = Vec::with_capacity(2);
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for &source_ty in &[a, b] {
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if source_ty != target_ty {
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obligations.push(Obligation::new(
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self.cause.clone(),
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self.param_env,
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ty::Binder::dummy(ty::PredicateKind::Coerce(ty::CoercePredicate {
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a: source_ty,
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b: target_ty,
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}))
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.to_predicate(self.tcx()),
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));
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}
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}
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debug!(
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"coerce_from_inference_variable: two inference variables, target_ty={:?}, obligations={:?}",
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target_ty, obligations
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);
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let adjustments = make_adjustments(target_ty);
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InferResult::Ok(InferOk { value: (adjustments, target_ty), obligations })
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} else {
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// One unresolved type variable: just apply subtyping, we may be able
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// to do something useful.
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self.unify_and(a, b, make_adjustments)
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}
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}
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/// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
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/// To match `A` with `B`, autoderef will be performed,
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/// calling `deref`/`deref_mut` where necessary.
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fn coerce_borrowed_pointer(
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&self,
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a: Ty<'tcx>,
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b: Ty<'tcx>,
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r_b: ty::Region<'tcx>,
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mutbl_b: hir::Mutability,
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) -> CoerceResult<'tcx> {
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debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
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// If we have a parameter of type `&M T_a` and the value
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// provided is `expr`, we will be adding an implicit borrow,
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// meaning that we convert `f(expr)` to `f(&M *expr)`. Therefore,
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// to type check, we will construct the type that `&M*expr` would
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// yield.
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let (r_a, mt_a) = match *a.kind() {
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ty::Ref(r_a, ty, mutbl) => {
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let mt_a = ty::TypeAndMut { ty, mutbl };
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coerce_mutbls(mt_a.mutbl, mutbl_b)?;
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(r_a, mt_a)
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}
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_ => return self.unify_and(a, b, identity),
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};
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let span = self.cause.span;
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let mut first_error = None;
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let mut r_borrow_var = None;
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let mut autoderef = self.autoderef(span, a);
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let mut found = None;
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for (referent_ty, autoderefs) in autoderef.by_ref() {
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if autoderefs == 0 {
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// Don't let this pass, otherwise it would cause
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// &T to autoref to &&T.
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continue;
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}
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// At this point, we have deref'd `a` to `referent_ty`. So
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// imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`.
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// In the autoderef loop for `&'a mut Vec<T>`, we would get
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// three callbacks:
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//
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// - `&'a mut Vec<T>` -- 0 derefs, just ignore it
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// - `Vec<T>` -- 1 deref
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// - `[T]` -- 2 deref
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//
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// At each point after the first callback, we want to
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// check to see whether this would match out target type
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// (`&'b mut [T]`) if we autoref'd it. We can't just
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// compare the referent types, though, because we still
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// have to consider the mutability. E.g., in the case
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// we've been considering, we have an `&mut` reference, so
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// the `T` in `[T]` needs to be unified with equality.
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//
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// Therefore, we construct reference types reflecting what
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// the types will be after we do the final auto-ref and
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// compare those. Note that this means we use the target
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// mutability [1], since it may be that we are coercing
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// from `&mut T` to `&U`.
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//
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// One fine point concerns the region that we use. We
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// choose the region such that the region of the final
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// type that results from `unify` will be the region we
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// want for the autoref:
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//
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// - if in sub mode, that means we want to use `'b` (the
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// region from the target reference) for both
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// pointers [2]. This is because sub mode (somewhat
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// arbitrarily) returns the subtype region. In the case
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// where we are coercing to a target type, we know we
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// want to use that target type region (`'b`) because --
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// for the program to type-check -- it must be the
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// smaller of the two.
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// - One fine point. It may be surprising that we can
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// use `'b` without relating `'a` and `'b`. The reason
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// that this is ok is that what we produce is
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// effectively a `&'b *x` expression (if you could
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// annotate the region of a borrow), and regionck has
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// code that adds edges from the region of a borrow
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// (`'b`, here) into the regions in the borrowed
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// expression (`*x`, here). (Search for "link".)
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// - if in lub mode, things can get fairly complicated. The
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// easiest thing is just to make a fresh
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// region variable [4], which effectively means we defer
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// the decision to region inference (and regionck, which will add
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// some more edges to this variable). However, this can wind up
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// creating a crippling number of variables in some cases --
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// e.g., #32278 -- so we optimize one particular case [3].
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// Let me try to explain with some examples:
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// - The "running example" above represents the simple case,
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// where we have one `&` reference at the outer level and
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// ownership all the rest of the way down. In this case,
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// we want `LUB('a, 'b)` as the resulting region.
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// - However, if there are nested borrows, that region is
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// too strong. Consider a coercion from `&'a &'x Rc<T>` to
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// `&'b T`. In this case, `'a` is actually irrelevant.
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// The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)`
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// we get spurious errors (`ui/regions-lub-ref-ref-rc.rs`).
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// (The errors actually show up in borrowck, typically, because
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// this extra edge causes the region `'a` to be inferred to something
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// too big, which then results in borrowck errors.)
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// - We could track the innermost shared reference, but there is already
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// code in regionck that has the job of creating links between
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// the region of a borrow and the regions in the thing being
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// borrowed (here, `'a` and `'x`), and it knows how to handle
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// all the various cases. So instead we just make a region variable
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// and let regionck figure it out.
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let r = if !self.use_lub {
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r_b // [2] above
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} else if autoderefs == 1 {
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r_a // [3] above
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} else {
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if r_borrow_var.is_none() {
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// create var lazily, at most once
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let coercion = Coercion(span);
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let r = self.next_region_var(coercion);
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r_borrow_var = Some(r); // [4] above
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}
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r_borrow_var.unwrap()
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};
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let derefd_ty_a = self.tcx.mk_ref(
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r,
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TypeAndMut {
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ty: referent_ty,
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mutbl: mutbl_b, // [1] above
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},
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);
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match self.unify(derefd_ty_a, b) {
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Ok(ok) => {
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found = Some(ok);
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break;
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}
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Err(err) => {
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if first_error.is_none() {
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first_error = Some(err);
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}
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}
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}
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}
|
|
|
|
// Extract type or return an error. We return the first error
|
|
// we got, which should be from relating the "base" type
|
|
// (e.g., in example above, the failure from relating `Vec<T>`
|
|
// to the target type), since that should be the least
|
|
// confusing.
|
|
let Some(InferOk { value: ty, mut obligations }) = found else {
|
|
let err = first_error.expect("coerce_borrowed_pointer had no error");
|
|
debug!("coerce_borrowed_pointer: failed with err = {:?}", err);
|
|
return Err(err);
|
|
};
|
|
|
|
if ty == a && mt_a.mutbl == hir::Mutability::Not && autoderef.step_count() == 1 {
|
|
// As a special case, if we would produce `&'a *x`, that's
|
|
// a total no-op. We end up with the type `&'a T` just as
|
|
// we started with. In that case, just skip it
|
|
// altogether. This is just an optimization.
|
|
//
|
|
// Note that for `&mut`, we DO want to reborrow --
|
|
// otherwise, this would be a move, which might be an
|
|
// error. For example `foo(self.x)` where `self` and
|
|
// `self.x` both have `&mut `type would be a move of
|
|
// `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
|
|
// which is a borrow.
|
|
assert_eq!(mutbl_b, hir::Mutability::Not); // can only coerce &T -> &U
|
|
return success(vec![], ty, obligations);
|
|
}
|
|
|
|
let InferOk { value: mut adjustments, obligations: o } =
|
|
self.adjust_steps_as_infer_ok(&autoderef);
|
|
obligations.extend(o);
|
|
obligations.extend(autoderef.into_obligations());
|
|
|
|
// Now apply the autoref. We have to extract the region out of
|
|
// the final ref type we got.
|
|
let ty::Ref(r_borrow, _, _) = ty.kind() else {
|
|
span_bug!(span, "expected a ref type, got {:?}", ty);
|
|
};
|
|
let mutbl = match mutbl_b {
|
|
hir::Mutability::Not => AutoBorrowMutability::Not,
|
|
hir::Mutability::Mut => {
|
|
AutoBorrowMutability::Mut { allow_two_phase_borrow: self.allow_two_phase }
|
|
}
|
|
};
|
|
adjustments.push(Adjustment {
|
|
kind: Adjust::Borrow(AutoBorrow::Ref(*r_borrow, mutbl)),
|
|
target: ty,
|
|
});
|
|
|
|
debug!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}", ty, adjustments);
|
|
|
|
success(adjustments, ty, obligations)
|
|
}
|
|
|
|
// &[T; n] or &mut [T; n] -> &[T]
|
|
// or &mut [T; n] -> &mut [T]
|
|
// or &Concrete -> &Trait, etc.
|
|
#[instrument(skip(self), level = "debug")]
|
|
fn coerce_unsized(&self, mut source: Ty<'tcx>, mut target: Ty<'tcx>) -> CoerceResult<'tcx> {
|
|
source = self.shallow_resolve(source);
|
|
target = self.shallow_resolve(target);
|
|
debug!(?source, ?target);
|
|
|
|
// These 'if' statements require some explanation.
|
|
// The `CoerceUnsized` trait is special - it is only
|
|
// possible to write `impl CoerceUnsized<B> for A` where
|
|
// A and B have 'matching' fields. This rules out the following
|
|
// two types of blanket impls:
|
|
//
|
|
// `impl<T> CoerceUnsized<T> for SomeType`
|
|
// `impl<T> CoerceUnsized<SomeType> for T`
|
|
//
|
|
// Both of these trigger a special `CoerceUnsized`-related error (E0376)
|
|
//
|
|
// We can take advantage of this fact to avoid performing unnecessary work.
|
|
// If either `source` or `target` is a type variable, then any applicable impl
|
|
// would need to be generic over the self-type (`impl<T> CoerceUnsized<SomeType> for T`)
|
|
// or generic over the `CoerceUnsized` type parameter (`impl<T> CoerceUnsized<T> for
|
|
// SomeType`).
|
|
//
|
|
// However, these are exactly the kinds of impls which are forbidden by
|
|
// the compiler! Therefore, we can be sure that coercion will always fail
|
|
// when either the source or target type is a type variable. This allows us
|
|
// to skip performing any trait selection, and immediately bail out.
|
|
if source.is_ty_var() {
|
|
debug!("coerce_unsized: source is a TyVar, bailing out");
|
|
return Err(TypeError::Mismatch);
|
|
}
|
|
if target.is_ty_var() {
|
|
debug!("coerce_unsized: target is a TyVar, bailing out");
|
|
return Err(TypeError::Mismatch);
|
|
}
|
|
|
|
let traits =
|
|
(self.tcx.lang_items().unsize_trait(), self.tcx.lang_items().coerce_unsized_trait());
|
|
let (Some(unsize_did), Some(coerce_unsized_did)) = traits else {
|
|
debug!("missing Unsize or CoerceUnsized traits");
|
|
return Err(TypeError::Mismatch);
|
|
};
|
|
|
|
// Note, we want to avoid unnecessary unsizing. We don't want to coerce to
|
|
// a DST unless we have to. This currently comes out in the wash since
|
|
// we can't unify [T] with U. But to properly support DST, we need to allow
|
|
// that, at which point we will need extra checks on the target here.
|
|
|
|
// Handle reborrows before selecting `Source: CoerceUnsized<Target>`.
|
|
let reborrow = match (source.kind(), target.kind()) {
|
|
(&ty::Ref(_, ty_a, mutbl_a), &ty::Ref(_, _, mutbl_b)) => {
|
|
coerce_mutbls(mutbl_a, mutbl_b)?;
|
|
|
|
let coercion = Coercion(self.cause.span);
|
|
let r_borrow = self.next_region_var(coercion);
|
|
let mutbl = match mutbl_b {
|
|
hir::Mutability::Not => AutoBorrowMutability::Not,
|
|
hir::Mutability::Mut => AutoBorrowMutability::Mut {
|
|
// We don't allow two-phase borrows here, at least for initial
|
|
// implementation. If it happens that this coercion is a function argument,
|
|
// the reborrow in coerce_borrowed_ptr will pick it up.
|
|
allow_two_phase_borrow: AllowTwoPhase::No,
|
|
},
|
|
};
|
|
Some((
|
|
Adjustment { kind: Adjust::Deref(None), target: ty_a },
|
|
Adjustment {
|
|
kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mutbl)),
|
|
target: self
|
|
.tcx
|
|
.mk_ref(r_borrow, ty::TypeAndMut { mutbl: mutbl_b, ty: ty_a }),
|
|
},
|
|
))
|
|
}
|
|
(&ty::Ref(_, ty_a, mt_a), &ty::RawPtr(ty::TypeAndMut { mutbl: mt_b, .. })) => {
|
|
coerce_mutbls(mt_a, mt_b)?;
|
|
|
|
Some((
|
|
Adjustment { kind: Adjust::Deref(None), target: ty_a },
|
|
Adjustment {
|
|
kind: Adjust::Borrow(AutoBorrow::RawPtr(mt_b)),
|
|
target: self.tcx.mk_ptr(ty::TypeAndMut { mutbl: mt_b, ty: ty_a }),
|
|
},
|
|
))
|
|
}
|
|
_ => None,
|
|
};
|
|
let coerce_source = reborrow.as_ref().map_or(source, |&(_, ref r)| r.target);
|
|
|
|
// Setup either a subtyping or a LUB relationship between
|
|
// the `CoerceUnsized` target type and the expected type.
|
|
// We only have the latter, so we use an inference variable
|
|
// for the former and let type inference do the rest.
|
|
let origin = TypeVariableOrigin {
|
|
kind: TypeVariableOriginKind::MiscVariable,
|
|
span: self.cause.span,
|
|
};
|
|
let coerce_target = self.next_ty_var(origin);
|
|
let mut coercion = self.unify_and(coerce_target, target, |target| {
|
|
let unsize = Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target };
|
|
match reborrow {
|
|
None => vec![unsize],
|
|
Some((ref deref, ref autoref)) => vec![deref.clone(), autoref.clone(), unsize],
|
|
}
|
|
})?;
|
|
|
|
let mut selcx = traits::SelectionContext::new(self);
|
|
|
|
// Create an obligation for `Source: CoerceUnsized<Target>`.
|
|
let cause = ObligationCause::new(
|
|
self.cause.span,
|
|
self.body_id,
|
|
ObligationCauseCode::Coercion { source, target },
|
|
);
|
|
|
|
// Use a FIFO queue for this custom fulfillment procedure.
|
|
//
|
|
// A Vec (or SmallVec) is not a natural choice for a queue. However,
|
|
// this code path is hot, and this queue usually has a max length of 1
|
|
// and almost never more than 3. By using a SmallVec we avoid an
|
|
// allocation, at the (very small) cost of (occasionally) having to
|
|
// shift subsequent elements down when removing the front element.
|
|
let mut queue: SmallVec<[_; 4]> = smallvec![traits::predicate_for_trait_def(
|
|
self.tcx,
|
|
self.fcx.param_env,
|
|
cause,
|
|
coerce_unsized_did,
|
|
0,
|
|
coerce_source,
|
|
&[coerce_target.into()]
|
|
)];
|
|
|
|
let mut has_unsized_tuple_coercion = false;
|
|
let mut has_trait_upcasting_coercion = None;
|
|
|
|
// Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
|
|
// emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where
|
|
// inference might unify those two inner type variables later.
|
|
let traits = [coerce_unsized_did, unsize_did];
|
|
while !queue.is_empty() {
|
|
let obligation = queue.remove(0);
|
|
debug!("coerce_unsized resolve step: {:?}", obligation);
|
|
let bound_predicate = obligation.predicate.kind();
|
|
let trait_pred = match bound_predicate.skip_binder() {
|
|
ty::PredicateKind::Trait(trait_pred) if traits.contains(&trait_pred.def_id()) => {
|
|
if unsize_did == trait_pred.def_id() {
|
|
let self_ty = trait_pred.self_ty();
|
|
let unsize_ty = trait_pred.trait_ref.substs[1].expect_ty();
|
|
if let (ty::Dynamic(ref data_a, ..), ty::Dynamic(ref data_b, ..)) =
|
|
(self_ty.kind(), unsize_ty.kind())
|
|
&& data_a.principal_def_id() != data_b.principal_def_id()
|
|
{
|
|
debug!("coerce_unsized: found trait upcasting coercion");
|
|
has_trait_upcasting_coercion = Some((self_ty, unsize_ty));
|
|
}
|
|
if let ty::Tuple(..) = unsize_ty.kind() {
|
|
debug!("coerce_unsized: found unsized tuple coercion");
|
|
has_unsized_tuple_coercion = true;
|
|
}
|
|
}
|
|
bound_predicate.rebind(trait_pred)
|
|
}
|
|
_ => {
|
|
coercion.obligations.push(obligation);
|
|
continue;
|
|
}
|
|
};
|
|
match selcx.select(&obligation.with(trait_pred)) {
|
|
// Uncertain or unimplemented.
|
|
Ok(None) => {
|
|
if trait_pred.def_id() == unsize_did {
|
|
let trait_pred = self.resolve_vars_if_possible(trait_pred);
|
|
let self_ty = trait_pred.skip_binder().self_ty();
|
|
let unsize_ty = trait_pred.skip_binder().trait_ref.substs[1].expect_ty();
|
|
debug!("coerce_unsized: ambiguous unsize case for {:?}", trait_pred);
|
|
match (&self_ty.kind(), &unsize_ty.kind()) {
|
|
(ty::Infer(ty::TyVar(v)), ty::Dynamic(..))
|
|
if self.type_var_is_sized(*v) =>
|
|
{
|
|
debug!("coerce_unsized: have sized infer {:?}", v);
|
|
coercion.obligations.push(obligation);
|
|
// `$0: Unsize<dyn Trait>` where we know that `$0: Sized`, try going
|
|
// for unsizing.
|
|
}
|
|
_ => {
|
|
// Some other case for `$0: Unsize<Something>`. Note that we
|
|
// hit this case even if `Something` is a sized type, so just
|
|
// don't do the coercion.
|
|
debug!("coerce_unsized: ambiguous unsize");
|
|
return Err(TypeError::Mismatch);
|
|
}
|
|
}
|
|
} else {
|
|
debug!("coerce_unsized: early return - ambiguous");
|
|
return Err(TypeError::Mismatch);
|
|
}
|
|
}
|
|
Err(traits::Unimplemented) => {
|
|
debug!("coerce_unsized: early return - can't prove obligation");
|
|
return Err(TypeError::Mismatch);
|
|
}
|
|
|
|
// Object safety violations or miscellaneous.
|
|
Err(err) => {
|
|
self.err_ctxt().report_selection_error(
|
|
obligation.clone(),
|
|
&obligation,
|
|
&err,
|
|
false,
|
|
);
|
|
// Treat this like an obligation and follow through
|
|
// with the unsizing - the lack of a coercion should
|
|
// be silent, as it causes a type mismatch later.
|
|
}
|
|
|
|
Ok(Some(impl_source)) => queue.extend(impl_source.nested_obligations()),
|
|
}
|
|
}
|
|
|
|
if has_unsized_tuple_coercion && !self.tcx.features().unsized_tuple_coercion {
|
|
feature_err(
|
|
&self.tcx.sess.parse_sess,
|
|
sym::unsized_tuple_coercion,
|
|
self.cause.span,
|
|
"unsized tuple coercion is not stable enough for use and is subject to change",
|
|
)
|
|
.emit();
|
|
}
|
|
|
|
if let Some((sub, sup)) = has_trait_upcasting_coercion
|
|
&& !self.tcx().features().trait_upcasting
|
|
{
|
|
// Renders better when we erase regions, since they're not really the point here.
|
|
let (sub, sup) = self.tcx.erase_regions((sub, sup));
|
|
let mut err = feature_err(
|
|
&self.tcx.sess.parse_sess,
|
|
sym::trait_upcasting,
|
|
self.cause.span,
|
|
&format!("cannot cast `{sub}` to `{sup}`, trait upcasting coercion is experimental"),
|
|
);
|
|
err.note(&format!("required when coercing `{source}` into `{target}`"));
|
|
err.emit();
|
|
}
|
|
|
|
Ok(coercion)
|
|
}
|
|
|
|
fn coerce_from_safe_fn<F, G>(
|
|
&self,
|
|
a: Ty<'tcx>,
|
|
fn_ty_a: ty::PolyFnSig<'tcx>,
|
|
b: Ty<'tcx>,
|
|
to_unsafe: F,
|
|
normal: G,
|
|
) -> CoerceResult<'tcx>
|
|
where
|
|
F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
|
|
G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
|
|
{
|
|
self.commit_if_ok(|snapshot| {
|
|
let result = if let ty::FnPtr(fn_ty_b) = b.kind()
|
|
&& let (hir::Unsafety::Normal, hir::Unsafety::Unsafe) =
|
|
(fn_ty_a.unsafety(), fn_ty_b.unsafety())
|
|
{
|
|
let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
|
|
self.unify_and(unsafe_a, b, to_unsafe)
|
|
} else {
|
|
self.unify_and(a, b, normal)
|
|
};
|
|
|
|
// FIXME(#73154): This is a hack. Currently LUB can generate
|
|
// unsolvable constraints. Additionally, it returns `a`
|
|
// unconditionally, even when the "LUB" is `b`. In the future, we
|
|
// want the coerced type to be the actual supertype of these two,
|
|
// but for now, we want to just error to ensure we don't lock
|
|
// ourselves into a specific behavior with NLL.
|
|
self.leak_check(false, snapshot)?;
|
|
|
|
result
|
|
})
|
|
}
|
|
|
|
fn coerce_from_fn_pointer(
|
|
&self,
|
|
a: Ty<'tcx>,
|
|
fn_ty_a: ty::PolyFnSig<'tcx>,
|
|
b: Ty<'tcx>,
|
|
) -> CoerceResult<'tcx> {
|
|
//! Attempts to coerce from the type of a Rust function item
|
|
//! into a closure or a `proc`.
|
|
//!
|
|
|
|
let b = self.shallow_resolve(b);
|
|
debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b);
|
|
|
|
self.coerce_from_safe_fn(
|
|
a,
|
|
fn_ty_a,
|
|
b,
|
|
simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)),
|
|
identity,
|
|
)
|
|
}
|
|
|
|
fn coerce_from_fn_item(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
|
|
//! Attempts to coerce from the type of a Rust function item
|
|
//! into a closure or a `proc`.
|
|
|
|
let b = self.shallow_resolve(b);
|
|
let InferOk { value: b, mut obligations } =
|
|
self.normalize_associated_types_in_as_infer_ok(self.cause.span, b);
|
|
debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b);
|
|
|
|
match b.kind() {
|
|
ty::FnPtr(b_sig) => {
|
|
let a_sig = a.fn_sig(self.tcx);
|
|
if let ty::FnDef(def_id, _) = *a.kind() {
|
|
// Intrinsics are not coercible to function pointers
|
|
if self.tcx.is_intrinsic(def_id) {
|
|
return Err(TypeError::IntrinsicCast);
|
|
}
|
|
|
|
// Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396).
|
|
|
|
if b_sig.unsafety() == hir::Unsafety::Normal
|
|
&& !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
|
|
{
|
|
return Err(TypeError::TargetFeatureCast(def_id));
|
|
}
|
|
}
|
|
|
|
let InferOk { value: a_sig, obligations: o1 } =
|
|
self.normalize_associated_types_in_as_infer_ok(self.cause.span, a_sig);
|
|
obligations.extend(o1);
|
|
|
|
let a_fn_pointer = self.tcx.mk_fn_ptr(a_sig);
|
|
let InferOk { value, obligations: o2 } = self.coerce_from_safe_fn(
|
|
a_fn_pointer,
|
|
a_sig,
|
|
b,
|
|
|unsafe_ty| {
|
|
vec![
|
|
Adjustment {
|
|
kind: Adjust::Pointer(PointerCast::ReifyFnPointer),
|
|
target: a_fn_pointer,
|
|
},
|
|
Adjustment {
|
|
kind: Adjust::Pointer(PointerCast::UnsafeFnPointer),
|
|
target: unsafe_ty,
|
|
},
|
|
]
|
|
},
|
|
simple(Adjust::Pointer(PointerCast::ReifyFnPointer)),
|
|
)?;
|
|
|
|
obligations.extend(o2);
|
|
Ok(InferOk { value, obligations })
|
|
}
|
|
_ => self.unify_and(a, b, identity),
|
|
}
|
|
}
|
|
|
|
fn coerce_closure_to_fn(
|
|
&self,
|
|
a: Ty<'tcx>,
|
|
closure_def_id_a: DefId,
|
|
substs_a: SubstsRef<'tcx>,
|
|
b: Ty<'tcx>,
|
|
) -> CoerceResult<'tcx> {
|
|
//! Attempts to coerce from the type of a non-capturing closure
|
|
//! into a function pointer.
|
|
//!
|
|
|
|
let b = self.shallow_resolve(b);
|
|
|
|
match b.kind() {
|
|
// At this point we haven't done capture analysis, which means
|
|
// that the ClosureSubsts just contains an inference variable instead
|
|
// of tuple of captured types.
|
|
//
|
|
// All we care here is if any variable is being captured and not the exact paths,
|
|
// so we check `upvars_mentioned` for root variables being captured.
|
|
ty::FnPtr(fn_ty)
|
|
if self
|
|
.tcx
|
|
.upvars_mentioned(closure_def_id_a.expect_local())
|
|
.map_or(true, |u| u.is_empty()) =>
|
|
{
|
|
// We coerce the closure, which has fn type
|
|
// `extern "rust-call" fn((arg0,arg1,...)) -> _`
|
|
// to
|
|
// `fn(arg0,arg1,...) -> _`
|
|
// or
|
|
// `unsafe fn(arg0,arg1,...) -> _`
|
|
let closure_sig = substs_a.as_closure().sig();
|
|
let unsafety = fn_ty.unsafety();
|
|
let pointer_ty =
|
|
self.tcx.mk_fn_ptr(self.tcx.signature_unclosure(closure_sig, unsafety));
|
|
debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})", a, b, pointer_ty);
|
|
self.unify_and(
|
|
pointer_ty,
|
|
b,
|
|
simple(Adjust::Pointer(PointerCast::ClosureFnPointer(unsafety))),
|
|
)
|
|
}
|
|
_ => self.unify_and(a, b, identity),
|
|
}
|
|
}
|
|
|
|
fn coerce_unsafe_ptr(
|
|
&self,
|
|
a: Ty<'tcx>,
|
|
b: Ty<'tcx>,
|
|
mutbl_b: hir::Mutability,
|
|
) -> CoerceResult<'tcx> {
|
|
debug!("coerce_unsafe_ptr(a={:?}, b={:?})", a, b);
|
|
|
|
let (is_ref, mt_a) = match *a.kind() {
|
|
ty::Ref(_, ty, mutbl) => (true, ty::TypeAndMut { ty, mutbl }),
|
|
ty::RawPtr(mt) => (false, mt),
|
|
_ => return self.unify_and(a, b, identity),
|
|
};
|
|
coerce_mutbls(mt_a.mutbl, mutbl_b)?;
|
|
|
|
// Check that the types which they point at are compatible.
|
|
let a_unsafe = self.tcx.mk_ptr(ty::TypeAndMut { mutbl: mutbl_b, ty: mt_a.ty });
|
|
// Although references and unsafe ptrs have the same
|
|
// representation, we still register an Adjust::DerefRef so that
|
|
// regionck knows that the region for `a` must be valid here.
|
|
if is_ref {
|
|
self.unify_and(a_unsafe, b, |target| {
|
|
vec![
|
|
Adjustment { kind: Adjust::Deref(None), target: mt_a.ty },
|
|
Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)), target },
|
|
]
|
|
})
|
|
} else if mt_a.mutbl != mutbl_b {
|
|
self.unify_and(a_unsafe, b, simple(Adjust::Pointer(PointerCast::MutToConstPointer)))
|
|
} else {
|
|
self.unify_and(a_unsafe, b, identity)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
|
|
/// Attempt to coerce an expression to a type, and return the
|
|
/// adjusted type of the expression, if successful.
|
|
/// Adjustments are only recorded if the coercion succeeded.
|
|
/// The expressions *must not* have any pre-existing adjustments.
|
|
pub fn try_coerce(
|
|
&self,
|
|
expr: &hir::Expr<'_>,
|
|
expr_ty: Ty<'tcx>,
|
|
target: Ty<'tcx>,
|
|
allow_two_phase: AllowTwoPhase,
|
|
cause: Option<ObligationCause<'tcx>>,
|
|
) -> RelateResult<'tcx, Ty<'tcx>> {
|
|
let source = self.resolve_vars_with_obligations(expr_ty);
|
|
debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target);
|
|
|
|
let cause =
|
|
cause.unwrap_or_else(|| self.cause(expr.span, ObligationCauseCode::ExprAssignable));
|
|
let coerce = Coerce::new(self, cause, allow_two_phase);
|
|
let ok = self.commit_if_ok(|_| coerce.coerce(source, target))?;
|
|
|
|
let (adjustments, _) = self.register_infer_ok_obligations(ok);
|
|
self.apply_adjustments(expr, adjustments);
|
|
Ok(if expr_ty.references_error() { self.tcx.ty_error() } else { target })
|
|
}
|
|
|
|
/// Same as `try_coerce()`, but without side-effects.
|
|
///
|
|
/// Returns false if the coercion creates any obligations that result in
|
|
/// errors.
|
|
pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
|
|
let source = self.resolve_vars_with_obligations(expr_ty);
|
|
debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
|
|
|
|
let cause = self.cause(rustc_span::DUMMY_SP, ObligationCauseCode::ExprAssignable);
|
|
// We don't ever need two-phase here since we throw out the result of the coercion
|
|
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
|
|
self.probe(|_| {
|
|
let Ok(ok) = coerce.coerce(source, target) else {
|
|
return false;
|
|
};
|
|
let mut fcx = traits::FulfillmentContext::new_in_snapshot();
|
|
fcx.register_predicate_obligations(self, ok.obligations);
|
|
fcx.select_where_possible(&self).is_empty()
|
|
})
|
|
}
|
|
|
|
/// Given a type and a target type, this function will calculate and return
|
|
/// how many dereference steps needed to achieve `expr_ty <: target`. If
|
|
/// it's not possible, return `None`.
|
|
pub fn deref_steps(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> Option<usize> {
|
|
let cause = self.cause(rustc_span::DUMMY_SP, ObligationCauseCode::ExprAssignable);
|
|
// We don't ever need two-phase here since we throw out the result of the coercion
|
|
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
|
|
coerce
|
|
.autoderef(rustc_span::DUMMY_SP, expr_ty)
|
|
.find_map(|(ty, steps)| self.probe(|_| coerce.unify(ty, target)).ok().map(|_| steps))
|
|
}
|
|
|
|
/// Given a type, this function will calculate and return the type given
|
|
/// for `<Ty as Deref>::Target` only if `Ty` also implements `DerefMut`.
|
|
///
|
|
/// This function is for diagnostics only, since it does not register
|
|
/// trait or region sub-obligations. (presumably we could, but it's not
|
|
/// particularly important for diagnostics...)
|
|
pub fn deref_once_mutably_for_diagnostic(&self, expr_ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
|
|
self.autoderef(rustc_span::DUMMY_SP, expr_ty).nth(1).and_then(|(deref_ty, _)| {
|
|
self.infcx
|
|
.type_implements_trait(
|
|
self.tcx.lang_items().deref_mut_trait()?,
|
|
expr_ty,
|
|
ty::List::empty(),
|
|
self.param_env,
|
|
)
|
|
.may_apply()
|
|
.then(|| deref_ty)
|
|
})
|
|
}
|
|
|
|
/// Given some expressions, their known unified type and another expression,
|
|
/// tries to unify the types, potentially inserting coercions on any of the
|
|
/// provided expressions and returns their LUB (aka "common supertype").
|
|
///
|
|
/// This is really an internal helper. From outside the coercion
|
|
/// module, you should instantiate a `CoerceMany` instance.
|
|
fn try_find_coercion_lub<E>(
|
|
&self,
|
|
cause: &ObligationCause<'tcx>,
|
|
exprs: &[E],
|
|
prev_ty: Ty<'tcx>,
|
|
new: &hir::Expr<'_>,
|
|
new_ty: Ty<'tcx>,
|
|
) -> RelateResult<'tcx, Ty<'tcx>>
|
|
where
|
|
E: AsCoercionSite,
|
|
{
|
|
let prev_ty = self.resolve_vars_with_obligations(prev_ty);
|
|
let new_ty = self.resolve_vars_with_obligations(new_ty);
|
|
debug!(
|
|
"coercion::try_find_coercion_lub({:?}, {:?}, exprs={:?} exprs)",
|
|
prev_ty,
|
|
new_ty,
|
|
exprs.len()
|
|
);
|
|
|
|
// The following check fixes #88097, where the compiler erroneously
|
|
// attempted to coerce a closure type to itself via a function pointer.
|
|
if prev_ty == new_ty {
|
|
return Ok(prev_ty);
|
|
}
|
|
|
|
// Special-case that coercion alone cannot handle:
|
|
// Function items or non-capturing closures of differing IDs or InternalSubsts.
|
|
let (a_sig, b_sig) = {
|
|
#[allow(rustc::usage_of_ty_tykind)]
|
|
let is_capturing_closure = |ty: &ty::TyKind<'tcx>| {
|
|
if let &ty::Closure(closure_def_id, _substs) = ty {
|
|
self.tcx.upvars_mentioned(closure_def_id.expect_local()).is_some()
|
|
} else {
|
|
false
|
|
}
|
|
};
|
|
if is_capturing_closure(prev_ty.kind()) || is_capturing_closure(new_ty.kind()) {
|
|
(None, None)
|
|
} else {
|
|
match (prev_ty.kind(), new_ty.kind()) {
|
|
(ty::FnDef(..), ty::FnDef(..)) => {
|
|
// Don't reify if the function types have a LUB, i.e., they
|
|
// are the same function and their parameters have a LUB.
|
|
match self
|
|
.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
|
|
{
|
|
// We have a LUB of prev_ty and new_ty, just return it.
|
|
Ok(ok) => return Ok(self.register_infer_ok_obligations(ok)),
|
|
Err(_) => {
|
|
(Some(prev_ty.fn_sig(self.tcx)), Some(new_ty.fn_sig(self.tcx)))
|
|
}
|
|
}
|
|
}
|
|
(ty::Closure(_, substs), ty::FnDef(..)) => {
|
|
let b_sig = new_ty.fn_sig(self.tcx);
|
|
let a_sig = self
|
|
.tcx
|
|
.signature_unclosure(substs.as_closure().sig(), b_sig.unsafety());
|
|
(Some(a_sig), Some(b_sig))
|
|
}
|
|
(ty::FnDef(..), ty::Closure(_, substs)) => {
|
|
let a_sig = prev_ty.fn_sig(self.tcx);
|
|
let b_sig = self
|
|
.tcx
|
|
.signature_unclosure(substs.as_closure().sig(), a_sig.unsafety());
|
|
(Some(a_sig), Some(b_sig))
|
|
}
|
|
(ty::Closure(_, substs_a), ty::Closure(_, substs_b)) => (
|
|
Some(self.tcx.signature_unclosure(
|
|
substs_a.as_closure().sig(),
|
|
hir::Unsafety::Normal,
|
|
)),
|
|
Some(self.tcx.signature_unclosure(
|
|
substs_b.as_closure().sig(),
|
|
hir::Unsafety::Normal,
|
|
)),
|
|
),
|
|
_ => (None, None),
|
|
}
|
|
}
|
|
};
|
|
if let (Some(a_sig), Some(b_sig)) = (a_sig, b_sig) {
|
|
// Intrinsics are not coercible to function pointers.
|
|
if a_sig.abi() == Abi::RustIntrinsic
|
|
|| a_sig.abi() == Abi::PlatformIntrinsic
|
|
|| b_sig.abi() == Abi::RustIntrinsic
|
|
|| b_sig.abi() == Abi::PlatformIntrinsic
|
|
{
|
|
return Err(TypeError::IntrinsicCast);
|
|
}
|
|
// The signature must match.
|
|
let a_sig = self.normalize_associated_types_in(new.span, a_sig);
|
|
let b_sig = self.normalize_associated_types_in(new.span, b_sig);
|
|
let sig = self
|
|
.at(cause, self.param_env)
|
|
.trace(prev_ty, new_ty)
|
|
.lub(a_sig, b_sig)
|
|
.map(|ok| self.register_infer_ok_obligations(ok))?;
|
|
|
|
// Reify both sides and return the reified fn pointer type.
|
|
let fn_ptr = self.tcx.mk_fn_ptr(sig);
|
|
let prev_adjustment = match prev_ty.kind() {
|
|
ty::Closure(..) => Adjust::Pointer(PointerCast::ClosureFnPointer(a_sig.unsafety())),
|
|
ty::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer),
|
|
_ => unreachable!(),
|
|
};
|
|
let next_adjustment = match new_ty.kind() {
|
|
ty::Closure(..) => Adjust::Pointer(PointerCast::ClosureFnPointer(b_sig.unsafety())),
|
|
ty::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer),
|
|
_ => unreachable!(),
|
|
};
|
|
for expr in exprs.iter().map(|e| e.as_coercion_site()) {
|
|
self.apply_adjustments(
|
|
expr,
|
|
vec![Adjustment { kind: prev_adjustment.clone(), target: fn_ptr }],
|
|
);
|
|
}
|
|
self.apply_adjustments(new, vec![Adjustment { kind: next_adjustment, target: fn_ptr }]);
|
|
return Ok(fn_ptr);
|
|
}
|
|
|
|
// Configure a Coerce instance to compute the LUB.
|
|
// We don't allow two-phase borrows on any autorefs this creates since we
|
|
// probably aren't processing function arguments here and even if we were,
|
|
// they're going to get autorefed again anyway and we can apply 2-phase borrows
|
|
// at that time.
|
|
let mut coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No);
|
|
coerce.use_lub = true;
|
|
|
|
// First try to coerce the new expression to the type of the previous ones,
|
|
// but only if the new expression has no coercion already applied to it.
|
|
let mut first_error = None;
|
|
if !self.typeck_results.borrow().adjustments().contains_key(new.hir_id) {
|
|
let result = self.commit_if_ok(|_| coerce.coerce(new_ty, prev_ty));
|
|
match result {
|
|
Ok(ok) => {
|
|
let (adjustments, target) = self.register_infer_ok_obligations(ok);
|
|
self.apply_adjustments(new, adjustments);
|
|
debug!(
|
|
"coercion::try_find_coercion_lub: was able to coerce from new type {:?} to previous type {:?} ({:?})",
|
|
new_ty, prev_ty, target
|
|
);
|
|
return Ok(target);
|
|
}
|
|
Err(e) => first_error = Some(e),
|
|
}
|
|
}
|
|
|
|
// Then try to coerce the previous expressions to the type of the new one.
|
|
// This requires ensuring there are no coercions applied to *any* of the
|
|
// previous expressions, other than noop reborrows (ignoring lifetimes).
|
|
for expr in exprs {
|
|
let expr = expr.as_coercion_site();
|
|
let noop = match self.typeck_results.borrow().expr_adjustments(expr) {
|
|
&[
|
|
Adjustment { kind: Adjust::Deref(_), .. },
|
|
Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mutbl_adj)), .. },
|
|
] => {
|
|
match *self.node_ty(expr.hir_id).kind() {
|
|
ty::Ref(_, _, mt_orig) => {
|
|
let mutbl_adj: hir::Mutability = mutbl_adj.into();
|
|
// Reborrow that we can safely ignore, because
|
|
// the next adjustment can only be a Deref
|
|
// which will be merged into it.
|
|
mutbl_adj == mt_orig
|
|
}
|
|
_ => false,
|
|
}
|
|
}
|
|
&[Adjustment { kind: Adjust::NeverToAny, .. }] | &[] => true,
|
|
_ => false,
|
|
};
|
|
|
|
if !noop {
|
|
debug!(
|
|
"coercion::try_find_coercion_lub: older expression {:?} had adjustments, requiring LUB",
|
|
expr,
|
|
);
|
|
|
|
return self
|
|
.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
|
|
.map(|ok| self.register_infer_ok_obligations(ok));
|
|
}
|
|
}
|
|
|
|
match self.commit_if_ok(|_| coerce.coerce(prev_ty, new_ty)) {
|
|
Err(_) => {
|
|
// Avoid giving strange errors on failed attempts.
|
|
if let Some(e) = first_error {
|
|
Err(e)
|
|
} else {
|
|
self.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
|
|
.map(|ok| self.register_infer_ok_obligations(ok))
|
|
}
|
|
}
|
|
Ok(ok) => {
|
|
let (adjustments, target) = self.register_infer_ok_obligations(ok);
|
|
for expr in exprs {
|
|
let expr = expr.as_coercion_site();
|
|
self.apply_adjustments(expr, adjustments.clone());
|
|
}
|
|
debug!(
|
|
"coercion::try_find_coercion_lub: was able to coerce previous type {:?} to new type {:?} ({:?})",
|
|
prev_ty, new_ty, target
|
|
);
|
|
Ok(target)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// CoerceMany encapsulates the pattern you should use when you have
|
|
/// many expressions that are all getting coerced to a common
|
|
/// type. This arises, for example, when you have a match (the result
|
|
/// of each arm is coerced to a common type). It also arises in less
|
|
/// obvious places, such as when you have many `break foo` expressions
|
|
/// that target the same loop, or the various `return` expressions in
|
|
/// a function.
|
|
///
|
|
/// The basic protocol is as follows:
|
|
///
|
|
/// - Instantiate the `CoerceMany` with an initial `expected_ty`.
|
|
/// This will also serve as the "starting LUB". The expectation is
|
|
/// that this type is something which all of the expressions *must*
|
|
/// be coercible to. Use a fresh type variable if needed.
|
|
/// - For each expression whose result is to be coerced, invoke `coerce()` with.
|
|
/// - In some cases we wish to coerce "non-expressions" whose types are implicitly
|
|
/// unit. This happens for example if you have a `break` with no expression,
|
|
/// or an `if` with no `else`. In that case, invoke `coerce_forced_unit()`.
|
|
/// - `coerce()` and `coerce_forced_unit()` may report errors. They hide this
|
|
/// from you so that you don't have to worry your pretty head about it.
|
|
/// But if an error is reported, the final type will be `err`.
|
|
/// - Invoking `coerce()` may cause us to go and adjust the "adjustments" on
|
|
/// previously coerced expressions.
|
|
/// - When all done, invoke `complete()`. This will return the LUB of
|
|
/// all your expressions.
|
|
/// - WARNING: I don't believe this final type is guaranteed to be
|
|
/// related to your initial `expected_ty` in any particular way,
|
|
/// although it will typically be a subtype, so you should check it.
|
|
/// - Invoking `complete()` may cause us to go and adjust the "adjustments" on
|
|
/// previously coerced expressions.
|
|
///
|
|
/// Example:
|
|
///
|
|
/// ```ignore (illustrative)
|
|
/// let mut coerce = CoerceMany::new(expected_ty);
|
|
/// for expr in exprs {
|
|
/// let expr_ty = fcx.check_expr_with_expectation(expr, expected);
|
|
/// coerce.coerce(fcx, &cause, expr, expr_ty);
|
|
/// }
|
|
/// let final_ty = coerce.complete(fcx);
|
|
/// ```
|
|
pub struct CoerceMany<'tcx, 'exprs, E: AsCoercionSite> {
|
|
expected_ty: Ty<'tcx>,
|
|
final_ty: Option<Ty<'tcx>>,
|
|
expressions: Expressions<'tcx, 'exprs, E>,
|
|
pushed: usize,
|
|
}
|
|
|
|
/// The type of a `CoerceMany` that is storing up the expressions into
|
|
/// a buffer. We use this in `check/mod.rs` for things like `break`.
|
|
pub type DynamicCoerceMany<'tcx> = CoerceMany<'tcx, 'tcx, &'tcx hir::Expr<'tcx>>;
|
|
|
|
enum Expressions<'tcx, 'exprs, E: AsCoercionSite> {
|
|
Dynamic(Vec<&'tcx hir::Expr<'tcx>>),
|
|
UpFront(&'exprs [E]),
|
|
}
|
|
|
|
impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
|
|
/// The usual case; collect the set of expressions dynamically.
|
|
/// If the full set of coercion sites is known before hand,
|
|
/// consider `with_coercion_sites()` instead to avoid allocation.
|
|
pub fn new(expected_ty: Ty<'tcx>) -> Self {
|
|
Self::make(expected_ty, Expressions::Dynamic(vec![]))
|
|
}
|
|
|
|
/// As an optimization, you can create a `CoerceMany` with a
|
|
/// pre-existing slice of expressions. In this case, you are
|
|
/// expected to pass each element in the slice to `coerce(...)` in
|
|
/// order. This is used with arrays in particular to avoid
|
|
/// needlessly cloning the slice.
|
|
pub fn with_coercion_sites(expected_ty: Ty<'tcx>, coercion_sites: &'exprs [E]) -> Self {
|
|
Self::make(expected_ty, Expressions::UpFront(coercion_sites))
|
|
}
|
|
|
|
fn make(expected_ty: Ty<'tcx>, expressions: Expressions<'tcx, 'exprs, E>) -> Self {
|
|
CoerceMany { expected_ty, final_ty: None, expressions, pushed: 0 }
|
|
}
|
|
|
|
/// Returns the "expected type" with which this coercion was
|
|
/// constructed. This represents the "downward propagated" type
|
|
/// that was given to us at the start of typing whatever construct
|
|
/// we are typing (e.g., the match expression).
|
|
///
|
|
/// Typically, this is used as the expected type when
|
|
/// type-checking each of the alternative expressions whose types
|
|
/// we are trying to merge.
|
|
pub fn expected_ty(&self) -> Ty<'tcx> {
|
|
self.expected_ty
|
|
}
|
|
|
|
/// Returns the current "merged type", representing our best-guess
|
|
/// at the LUB of the expressions we've seen so far (if any). This
|
|
/// isn't *final* until you call `self.complete()`, which will return
|
|
/// the merged type.
|
|
pub fn merged_ty(&self) -> Ty<'tcx> {
|
|
self.final_ty.unwrap_or(self.expected_ty)
|
|
}
|
|
|
|
/// Indicates that the value generated by `expression`, which is
|
|
/// of type `expression_ty`, is one of the possibilities that we
|
|
/// could coerce from. This will record `expression`, and later
|
|
/// calls to `coerce` may come back and add adjustments and things
|
|
/// if necessary.
|
|
pub fn coerce<'a>(
|
|
&mut self,
|
|
fcx: &FnCtxt<'a, 'tcx>,
|
|
cause: &ObligationCause<'tcx>,
|
|
expression: &'tcx hir::Expr<'tcx>,
|
|
expression_ty: Ty<'tcx>,
|
|
) {
|
|
self.coerce_inner(fcx, cause, Some(expression), expression_ty, None, false)
|
|
}
|
|
|
|
/// Indicates that one of the inputs is a "forced unit". This
|
|
/// occurs in a case like `if foo { ... };`, where the missing else
|
|
/// generates a "forced unit". Another example is a `loop { break;
|
|
/// }`, where the `break` has no argument expression. We treat
|
|
/// these cases slightly differently for error-reporting
|
|
/// purposes. Note that these tend to correspond to cases where
|
|
/// the `()` expression is implicit in the source, and hence we do
|
|
/// not take an expression argument.
|
|
///
|
|
/// The `augment_error` gives you a chance to extend the error
|
|
/// message, in case any results (e.g., we use this to suggest
|
|
/// removing a `;`).
|
|
pub fn coerce_forced_unit<'a>(
|
|
&mut self,
|
|
fcx: &FnCtxt<'a, 'tcx>,
|
|
cause: &ObligationCause<'tcx>,
|
|
augment_error: &mut dyn FnMut(&mut Diagnostic),
|
|
label_unit_as_expected: bool,
|
|
) {
|
|
self.coerce_inner(
|
|
fcx,
|
|
cause,
|
|
None,
|
|
fcx.tcx.mk_unit(),
|
|
Some(augment_error),
|
|
label_unit_as_expected,
|
|
)
|
|
}
|
|
|
|
/// The inner coercion "engine". If `expression` is `None`, this
|
|
/// is a forced-unit case, and hence `expression_ty` must be
|
|
/// `Nil`.
|
|
#[instrument(skip(self, fcx, augment_error, label_expression_as_expected), level = "debug")]
|
|
pub(crate) fn coerce_inner<'a>(
|
|
&mut self,
|
|
fcx: &FnCtxt<'a, 'tcx>,
|
|
cause: &ObligationCause<'tcx>,
|
|
expression: Option<&'tcx hir::Expr<'tcx>>,
|
|
mut expression_ty: Ty<'tcx>,
|
|
augment_error: Option<&mut dyn FnMut(&mut Diagnostic)>,
|
|
label_expression_as_expected: bool,
|
|
) {
|
|
// Incorporate whatever type inference information we have
|
|
// until now; in principle we might also want to process
|
|
// pending obligations, but doing so should only improve
|
|
// compatibility (hopefully that is true) by helping us
|
|
// uncover never types better.
|
|
if expression_ty.is_ty_var() {
|
|
expression_ty = fcx.infcx.shallow_resolve(expression_ty);
|
|
}
|
|
|
|
// If we see any error types, just propagate that error
|
|
// upwards.
|
|
if expression_ty.references_error() || self.merged_ty().references_error() {
|
|
self.final_ty = Some(fcx.tcx.ty_error());
|
|
return;
|
|
}
|
|
|
|
// Handle the actual type unification etc.
|
|
let result = if let Some(expression) = expression {
|
|
if self.pushed == 0 {
|
|
// Special-case the first expression we are coercing.
|
|
// To be honest, I'm not entirely sure why we do this.
|
|
// We don't allow two-phase borrows, see comment in try_find_coercion_lub for why
|
|
fcx.try_coerce(
|
|
expression,
|
|
expression_ty,
|
|
self.expected_ty,
|
|
AllowTwoPhase::No,
|
|
Some(cause.clone()),
|
|
)
|
|
} else {
|
|
match self.expressions {
|
|
Expressions::Dynamic(ref exprs) => fcx.try_find_coercion_lub(
|
|
cause,
|
|
exprs,
|
|
self.merged_ty(),
|
|
expression,
|
|
expression_ty,
|
|
),
|
|
Expressions::UpFront(ref coercion_sites) => fcx.try_find_coercion_lub(
|
|
cause,
|
|
&coercion_sites[0..self.pushed],
|
|
self.merged_ty(),
|
|
expression,
|
|
expression_ty,
|
|
),
|
|
}
|
|
}
|
|
} else {
|
|
// this is a hack for cases where we default to `()` because
|
|
// the expression etc has been omitted from the source. An
|
|
// example is an `if let` without an else:
|
|
//
|
|
// if let Some(x) = ... { }
|
|
//
|
|
// we wind up with a second match arm that is like `_ =>
|
|
// ()`. That is the case we are considering here. We take
|
|
// a different path to get the right "expected, found"
|
|
// message and so forth (and because we know that
|
|
// `expression_ty` will be unit).
|
|
//
|
|
// Another example is `break` with no argument expression.
|
|
assert!(expression_ty.is_unit(), "if let hack without unit type");
|
|
fcx.at(cause, fcx.param_env)
|
|
.eq_exp(label_expression_as_expected, expression_ty, self.merged_ty())
|
|
.map(|infer_ok| {
|
|
fcx.register_infer_ok_obligations(infer_ok);
|
|
expression_ty
|
|
})
|
|
};
|
|
|
|
debug!(?result);
|
|
match result {
|
|
Ok(v) => {
|
|
self.final_ty = Some(v);
|
|
if let Some(e) = expression {
|
|
match self.expressions {
|
|
Expressions::Dynamic(ref mut buffer) => buffer.push(e),
|
|
Expressions::UpFront(coercion_sites) => {
|
|
// if the user gave us an array to validate, check that we got
|
|
// the next expression in the list, as expected
|
|
assert_eq!(
|
|
coercion_sites[self.pushed].as_coercion_site().hir_id,
|
|
e.hir_id
|
|
);
|
|
}
|
|
}
|
|
self.pushed += 1;
|
|
}
|
|
}
|
|
Err(coercion_error) => {
|
|
// Mark that we've failed to coerce the types here to suppress
|
|
// any superfluous errors we might encounter while trying to
|
|
// emit or provide suggestions on how to fix the initial error.
|
|
fcx.set_tainted_by_errors();
|
|
let (expected, found) = if label_expression_as_expected {
|
|
// In the case where this is a "forced unit", like
|
|
// `break`, we want to call the `()` "expected"
|
|
// since it is implied by the syntax.
|
|
// (Note: not all force-units work this way.)"
|
|
(expression_ty, self.merged_ty())
|
|
} else {
|
|
// Otherwise, the "expected" type for error
|
|
// reporting is the current unification type,
|
|
// which is basically the LUB of the expressions
|
|
// we've seen so far (combined with the expected
|
|
// type)
|
|
(self.merged_ty(), expression_ty)
|
|
};
|
|
let (expected, found) = fcx.resolve_vars_if_possible((expected, found));
|
|
|
|
let mut err;
|
|
let mut unsized_return = false;
|
|
let mut visitor = CollectRetsVisitor { ret_exprs: vec![] };
|
|
match *cause.code() {
|
|
ObligationCauseCode::ReturnNoExpression => {
|
|
err = struct_span_err!(
|
|
fcx.tcx.sess,
|
|
cause.span,
|
|
E0069,
|
|
"`return;` in a function whose return type is not `()`"
|
|
);
|
|
err.span_label(cause.span, "return type is not `()`");
|
|
}
|
|
ObligationCauseCode::BlockTailExpression(blk_id) => {
|
|
let parent_id = fcx.tcx.hir().get_parent_node(blk_id);
|
|
err = self.report_return_mismatched_types(
|
|
cause,
|
|
expected,
|
|
found,
|
|
coercion_error.clone(),
|
|
fcx,
|
|
parent_id,
|
|
expression,
|
|
Some(blk_id),
|
|
);
|
|
if !fcx.tcx.features().unsized_locals {
|
|
unsized_return = self.is_return_ty_unsized(fcx, blk_id);
|
|
}
|
|
if let Some(expression) = expression
|
|
&& let hir::ExprKind::Loop(loop_blk, ..) = expression.kind {
|
|
intravisit::walk_block(& mut visitor, loop_blk);
|
|
}
|
|
}
|
|
ObligationCauseCode::ReturnValue(id) => {
|
|
err = self.report_return_mismatched_types(
|
|
cause,
|
|
expected,
|
|
found,
|
|
coercion_error.clone(),
|
|
fcx,
|
|
id,
|
|
expression,
|
|
None,
|
|
);
|
|
if !fcx.tcx.features().unsized_locals {
|
|
let id = fcx.tcx.hir().get_parent_node(id);
|
|
unsized_return = self.is_return_ty_unsized(fcx, id);
|
|
}
|
|
}
|
|
_ => {
|
|
err = fcx.err_ctxt().report_mismatched_types(
|
|
cause,
|
|
expected,
|
|
found,
|
|
coercion_error.clone(),
|
|
);
|
|
}
|
|
}
|
|
|
|
if let Some(augment_error) = augment_error {
|
|
augment_error(&mut err);
|
|
}
|
|
|
|
let is_insufficiently_polymorphic =
|
|
matches!(coercion_error, TypeError::RegionsInsufficientlyPolymorphic(..));
|
|
|
|
if !is_insufficiently_polymorphic && let Some(expr) = expression {
|
|
fcx.emit_coerce_suggestions(
|
|
&mut err,
|
|
expr,
|
|
found,
|
|
expected,
|
|
None,
|
|
Some(coercion_error),
|
|
);
|
|
}
|
|
|
|
if visitor.ret_exprs.len() > 0 && let Some(expr) = expression {
|
|
self.note_unreachable_loop_return(&mut err, &expr, &visitor.ret_exprs);
|
|
}
|
|
err.emit_unless(unsized_return);
|
|
|
|
self.final_ty = Some(fcx.tcx.ty_error());
|
|
}
|
|
}
|
|
}
|
|
fn note_unreachable_loop_return(
|
|
&self,
|
|
err: &mut Diagnostic,
|
|
expr: &hir::Expr<'tcx>,
|
|
ret_exprs: &Vec<&'tcx hir::Expr<'tcx>>,
|
|
) {
|
|
let hir::ExprKind::Loop(_, _, _, loop_span) = expr.kind else { return;};
|
|
let mut span: MultiSpan = vec![loop_span].into();
|
|
span.push_span_label(loop_span, "this might have zero elements to iterate on");
|
|
const MAXITER: usize = 3;
|
|
let iter = ret_exprs.iter().take(MAXITER);
|
|
for ret_expr in iter {
|
|
span.push_span_label(
|
|
ret_expr.span,
|
|
"if the loop doesn't execute, this value would never get returned",
|
|
);
|
|
}
|
|
err.span_note(
|
|
span,
|
|
"the function expects a value to always be returned, but loops might run zero times",
|
|
);
|
|
if MAXITER < ret_exprs.len() {
|
|
err.note(&format!(
|
|
"if the loop doesn't execute, {} other values would never get returned",
|
|
ret_exprs.len() - MAXITER
|
|
));
|
|
}
|
|
err.help(
|
|
"return a value for the case when the loop has zero elements to iterate on, or \
|
|
consider changing the return type to account for that possibility",
|
|
);
|
|
}
|
|
|
|
fn report_return_mismatched_types<'a>(
|
|
&self,
|
|
cause: &ObligationCause<'tcx>,
|
|
expected: Ty<'tcx>,
|
|
found: Ty<'tcx>,
|
|
ty_err: TypeError<'tcx>,
|
|
fcx: &FnCtxt<'a, 'tcx>,
|
|
id: hir::HirId,
|
|
expression: Option<&'tcx hir::Expr<'tcx>>,
|
|
blk_id: Option<hir::HirId>,
|
|
) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
|
|
let mut err = fcx.err_ctxt().report_mismatched_types(cause, expected, found, ty_err);
|
|
|
|
let mut pointing_at_return_type = false;
|
|
let mut fn_output = None;
|
|
|
|
let parent_id = fcx.tcx.hir().get_parent_node(id);
|
|
let parent = fcx.tcx.hir().get(parent_id);
|
|
if let Some(expr) = expression
|
|
&& let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(&hir::Closure { body, .. }), .. }) = parent
|
|
&& !matches!(fcx.tcx.hir().body(body).value.kind, hir::ExprKind::Block(..))
|
|
{
|
|
fcx.suggest_missing_semicolon(&mut err, expr, expected, true);
|
|
}
|
|
// Verify that this is a tail expression of a function, otherwise the
|
|
// label pointing out the cause for the type coercion will be wrong
|
|
// as prior return coercions would not be relevant (#57664).
|
|
let fn_decl = if let (Some(expr), Some(blk_id)) = (expression, blk_id) {
|
|
pointing_at_return_type =
|
|
fcx.suggest_mismatched_types_on_tail(&mut err, expr, expected, found, blk_id);
|
|
if let (Some(cond_expr), true, false) = (
|
|
fcx.tcx.hir().get_if_cause(expr.hir_id),
|
|
expected.is_unit(),
|
|
pointing_at_return_type,
|
|
)
|
|
// If the block is from an external macro or try (`?`) desugaring, then
|
|
// do not suggest adding a semicolon, because there's nowhere to put it.
|
|
// See issues #81943 and #87051.
|
|
&& matches!(
|
|
cond_expr.span.desugaring_kind(),
|
|
None | Some(DesugaringKind::WhileLoop)
|
|
) && !in_external_macro(fcx.tcx.sess, cond_expr.span)
|
|
&& !matches!(
|
|
cond_expr.kind,
|
|
hir::ExprKind::Match(.., hir::MatchSource::TryDesugar)
|
|
)
|
|
{
|
|
err.span_label(cond_expr.span, "expected this to be `()`");
|
|
if expr.can_have_side_effects() {
|
|
fcx.suggest_semicolon_at_end(cond_expr.span, &mut err);
|
|
}
|
|
}
|
|
fcx.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
|
|
} else {
|
|
fcx.get_fn_decl(parent_id)
|
|
};
|
|
|
|
if let Some((fn_decl, can_suggest)) = fn_decl {
|
|
if blk_id.is_none() {
|
|
pointing_at_return_type |= fcx.suggest_missing_return_type(
|
|
&mut err,
|
|
&fn_decl,
|
|
expected,
|
|
found,
|
|
can_suggest,
|
|
fcx.tcx.hir().get_parent_item(id).into(),
|
|
);
|
|
}
|
|
if !pointing_at_return_type {
|
|
fn_output = Some(&fn_decl.output); // `impl Trait` return type
|
|
}
|
|
}
|
|
|
|
let parent_id = fcx.tcx.hir().get_parent_item(id);
|
|
let parent_item = fcx.tcx.hir().get_by_def_id(parent_id.def_id);
|
|
|
|
if let (Some(expr), Some(_), Some((fn_decl, _, _))) =
|
|
(expression, blk_id, fcx.get_node_fn_decl(parent_item))
|
|
{
|
|
fcx.suggest_missing_break_or_return_expr(
|
|
&mut err,
|
|
expr,
|
|
fn_decl,
|
|
expected,
|
|
found,
|
|
id,
|
|
parent_id.into(),
|
|
);
|
|
}
|
|
|
|
let ret_coercion_span = fcx.ret_coercion_span.get();
|
|
|
|
if let Some(sp) = ret_coercion_span
|
|
// If the closure has an explicit return type annotation, or if
|
|
// the closure's return type has been inferred from outside
|
|
// requirements (such as an Fn* trait bound), then a type error
|
|
// may occur at the first return expression we see in the closure
|
|
// (if it conflicts with the declared return type). Skip adding a
|
|
// note in this case, since it would be incorrect.
|
|
&& !fcx.return_type_pre_known
|
|
{
|
|
err.span_note(
|
|
sp,
|
|
&format!(
|
|
"return type inferred to be `{}` here",
|
|
expected
|
|
),
|
|
);
|
|
}
|
|
|
|
if let (Some(sp), Some(fn_output)) = (ret_coercion_span, fn_output) {
|
|
self.add_impl_trait_explanation(&mut err, cause, fcx, expected, sp, fn_output);
|
|
}
|
|
|
|
err
|
|
}
|
|
|
|
fn add_impl_trait_explanation<'a>(
|
|
&self,
|
|
err: &mut Diagnostic,
|
|
cause: &ObligationCause<'tcx>,
|
|
fcx: &FnCtxt<'a, 'tcx>,
|
|
expected: Ty<'tcx>,
|
|
sp: Span,
|
|
fn_output: &hir::FnRetTy<'_>,
|
|
) {
|
|
let return_sp = fn_output.span();
|
|
err.span_label(return_sp, "expected because this return type...");
|
|
err.span_label(
|
|
sp,
|
|
format!("...is found to be `{}` here", fcx.resolve_vars_with_obligations(expected)),
|
|
);
|
|
let impl_trait_msg = "for information on `impl Trait`, see \
|
|
<https://doc.rust-lang.org/book/ch10-02-traits.html\
|
|
#returning-types-that-implement-traits>";
|
|
let trait_obj_msg = "for information on trait objects, see \
|
|
<https://doc.rust-lang.org/book/ch17-02-trait-objects.html\
|
|
#using-trait-objects-that-allow-for-values-of-different-types>";
|
|
err.note("to return `impl Trait`, all returned values must be of the same type");
|
|
err.note(impl_trait_msg);
|
|
let snippet = fcx
|
|
.tcx
|
|
.sess
|
|
.source_map()
|
|
.span_to_snippet(return_sp)
|
|
.unwrap_or_else(|_| "dyn Trait".to_string());
|
|
let mut snippet_iter = snippet.split_whitespace();
|
|
let has_impl = snippet_iter.next().map_or(false, |s| s == "impl");
|
|
// Only suggest `Box<dyn Trait>` if `Trait` in `impl Trait` is object safe.
|
|
let mut is_object_safe = false;
|
|
if let hir::FnRetTy::Return(ty) = fn_output
|
|
// Get the return type.
|
|
&& let hir::TyKind::OpaqueDef(..) = ty.kind
|
|
{
|
|
let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty);
|
|
// Get the `impl Trait`'s `DefId`.
|
|
if let ty::Opaque(def_id, _) = ty.kind()
|
|
// Get the `impl Trait`'s `Item` so that we can get its trait bounds and
|
|
// get the `Trait`'s `DefId`.
|
|
&& let hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }) =
|
|
fcx.tcx.hir().expect_item(def_id.expect_local()).kind
|
|
{
|
|
// Are of this `impl Trait`'s traits object safe?
|
|
is_object_safe = bounds.iter().all(|bound| {
|
|
bound
|
|
.trait_ref()
|
|
.and_then(|t| t.trait_def_id())
|
|
.map_or(false, |def_id| {
|
|
fcx.tcx.object_safety_violations(def_id).is_empty()
|
|
})
|
|
})
|
|
}
|
|
};
|
|
if has_impl {
|
|
if is_object_safe {
|
|
err.multipart_suggestion(
|
|
"you could change the return type to be a boxed trait object",
|
|
vec![
|
|
(return_sp.with_hi(return_sp.lo() + BytePos(4)), "Box<dyn".to_string()),
|
|
(return_sp.shrink_to_hi(), ">".to_string()),
|
|
],
|
|
Applicability::MachineApplicable,
|
|
);
|
|
let sugg = [sp, cause.span]
|
|
.into_iter()
|
|
.flat_map(|sp| {
|
|
[
|
|
(sp.shrink_to_lo(), "Box::new(".to_string()),
|
|
(sp.shrink_to_hi(), ")".to_string()),
|
|
]
|
|
.into_iter()
|
|
})
|
|
.collect::<Vec<_>>();
|
|
err.multipart_suggestion(
|
|
"if you change the return type to expect trait objects, box the returned \
|
|
expressions",
|
|
sugg,
|
|
Applicability::MaybeIncorrect,
|
|
);
|
|
} else {
|
|
err.help(&format!(
|
|
"if the trait `{}` were object safe, you could return a boxed trait object",
|
|
&snippet[5..]
|
|
));
|
|
}
|
|
err.note(trait_obj_msg);
|
|
}
|
|
err.help("you could instead create a new `enum` with a variant for each returned type");
|
|
}
|
|
|
|
fn is_return_ty_unsized<'a>(&self, fcx: &FnCtxt<'a, 'tcx>, blk_id: hir::HirId) -> bool {
|
|
if let Some((fn_decl, _)) = fcx.get_fn_decl(blk_id)
|
|
&& let hir::FnRetTy::Return(ty) = fn_decl.output
|
|
&& let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty)
|
|
&& let ty::Dynamic(..) = ty.kind()
|
|
{
|
|
return true;
|
|
}
|
|
false
|
|
}
|
|
|
|
pub fn complete<'a>(self, fcx: &FnCtxt<'a, 'tcx>) -> Ty<'tcx> {
|
|
if let Some(final_ty) = self.final_ty {
|
|
final_ty
|
|
} else {
|
|
// If we only had inputs that were of type `!` (or no
|
|
// inputs at all), then the final type is `!`.
|
|
assert_eq!(self.pushed, 0);
|
|
fcx.tcx.types.never
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Something that can be converted into an expression to which we can
|
|
/// apply a coercion.
|
|
pub trait AsCoercionSite {
|
|
fn as_coercion_site(&self) -> &hir::Expr<'_>;
|
|
}
|
|
|
|
impl AsCoercionSite for hir::Expr<'_> {
|
|
fn as_coercion_site(&self) -> &hir::Expr<'_> {
|
|
self
|
|
}
|
|
}
|
|
|
|
impl<'a, T> AsCoercionSite for &'a T
|
|
where
|
|
T: AsCoercionSite,
|
|
{
|
|
fn as_coercion_site(&self) -> &hir::Expr<'_> {
|
|
(**self).as_coercion_site()
|
|
}
|
|
}
|
|
|
|
impl AsCoercionSite for ! {
|
|
fn as_coercion_site(&self) -> &hir::Expr<'_> {
|
|
unreachable!()
|
|
}
|
|
}
|
|
|
|
impl AsCoercionSite for hir::Arm<'_> {
|
|
fn as_coercion_site(&self) -> &hir::Expr<'_> {
|
|
&self.body
|
|
}
|
|
}
|