Move trait selection error reporting to its own top-level module

compiler/rustc_trait_selection/src/error_reporting/mod.rs

@@ -0,0 +1 @@
+pub mod traits;

compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs

@@ -0,0 +1,136 @@
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer::{BoundRegionConversionTime, InferCtxt};
+use rustc_infer::traits::util::elaborate;
+use rustc_infer::traits::{Obligation, ObligationCause, PolyTraitObligation};
+use rustc_middle::ty;
+use rustc_span::{Span, DUMMY_SP};
+
+use crate::traits::query::evaluate_obligation::InferCtxtExt;
+use crate::traits::ObligationCtxt;
+
+#[derive(Debug)]
+pub enum CandidateSource {
+    DefId(DefId),
+    ParamEnv(Span),
+}
+
+pub fn compute_applicable_impls_for_diagnostics<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    obligation: &PolyTraitObligation<'tcx>,
+) -> Vec<CandidateSource> {
+    let tcx = infcx.tcx;
+    let param_env = obligation.param_env;
+
+    let predicate_polarity = obligation.predicate.skip_binder().polarity;
+
+    let impl_may_apply = |impl_def_id| {
+        let ocx = ObligationCtxt::new(infcx);
+        infcx.enter_forall(obligation.predicate, |placeholder_obligation| {
+            let obligation_trait_ref = ocx.normalize(
+                &ObligationCause::dummy(),
+                param_env,
+                placeholder_obligation.trait_ref,
+            );
+
+            let impl_args = infcx.fresh_args_for_item(DUMMY_SP, impl_def_id);
+            let impl_trait_ref =
+                tcx.impl_trait_ref(impl_def_id).unwrap().instantiate(tcx, impl_args);
+            let impl_trait_ref =
+                ocx.normalize(&ObligationCause::dummy(), param_env, impl_trait_ref);
+
+            if let Err(_) =
+                ocx.eq(&ObligationCause::dummy(), param_env, obligation_trait_ref, impl_trait_ref)
+            {
+                return false;
+            }
+
+            let impl_trait_header = tcx.impl_trait_header(impl_def_id).unwrap();
+            let impl_polarity = impl_trait_header.polarity;
+
+            match (impl_polarity, predicate_polarity) {
+                (ty::ImplPolarity::Positive, ty::PredicatePolarity::Positive)
+                | (ty::ImplPolarity::Negative, ty::PredicatePolarity::Negative) => {}
+                _ => return false,
+            }
+
+            let obligations = tcx
+                .predicates_of(impl_def_id)
+                .instantiate(tcx, impl_args)
+                .into_iter()
+                .map(|(predicate, _)| {
+                    Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate)
+                })
+                // Kinda hacky, but let's just throw away obligations that overflow.
+                // This may reduce the accuracy of this check (if the obligation guides
+                // inference or it actually resulted in error after others are processed)
+                // ... but this is diagnostics code.
+                .filter(|obligation| {
+                    infcx.next_trait_solver() || infcx.evaluate_obligation(obligation).is_ok()
+                });
+            ocx.register_obligations(obligations);
+
+            ocx.select_where_possible().is_empty()
+        })
+    };
+
+    let param_env_candidate_may_apply = |poly_trait_predicate: ty::PolyTraitPredicate<'tcx>| {
+        let ocx = ObligationCtxt::new(infcx);
+        infcx.enter_forall(obligation.predicate, |placeholder_obligation| {
+            let obligation_trait_ref = ocx.normalize(
+                &ObligationCause::dummy(),
+                param_env,
+                placeholder_obligation.trait_ref,
+            );
+
+            let param_env_predicate = infcx.instantiate_binder_with_fresh_vars(
+                DUMMY_SP,
+                BoundRegionConversionTime::HigherRankedType,
+                poly_trait_predicate,
+            );
+            let param_env_trait_ref =
+                ocx.normalize(&ObligationCause::dummy(), param_env, param_env_predicate.trait_ref);
+
+            if let Err(_) = ocx.eq(
+                &ObligationCause::dummy(),
+                param_env,
+                obligation_trait_ref,
+                param_env_trait_ref,
+            ) {
+                return false;
+            }
+
+            ocx.select_where_possible().is_empty()
+        })
+    };
+
+    let mut ambiguities = Vec::new();
+
+    tcx.for_each_relevant_impl(
+        obligation.predicate.def_id(),
+        obligation.predicate.skip_binder().trait_ref.self_ty(),
+        |impl_def_id| {
+            if infcx.probe(|_| impl_may_apply(impl_def_id)) {
+                ambiguities.push(CandidateSource::DefId(impl_def_id))
+            }
+        },
+    );
+
+    let predicates =
+        tcx.predicates_of(obligation.cause.body_id.to_def_id()).instantiate_identity(tcx);
+    for (pred, span) in elaborate(tcx, predicates.into_iter()) {
+        let kind = pred.kind();
+        if let ty::ClauseKind::Trait(trait_pred) = kind.skip_binder()
+            && param_env_candidate_may_apply(kind.rebind(trait_pred))
+        {
+            if kind.rebind(trait_pred.trait_ref)
+                == ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_pred.def_id()))
+            {
+                ambiguities.push(CandidateSource::ParamEnv(tcx.def_span(trait_pred.def_id())))
+            } else {
+                ambiguities.push(CandidateSource::ParamEnv(span))
+            }
+        }
+    }
+
+    ambiguities
+}

compiler/rustc_trait_selection/src/error_reporting/traits/infer_ctxt_ext.rs

@@ -0,0 +1,244 @@
+use crate::infer::InferCtxt;
+use crate::traits::{Obligation, ObligationCause, ObligationCtxt};
+use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, Diag};
+use rustc_hir as hir;
+use rustc_hir::Node;
+use rustc_macros::extension;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::{Span, DUMMY_SP};
+
+use super::ArgKind;
+
+pub use rustc_infer::traits::error_reporting::*;
+
+#[extension(pub trait InferCtxtExt<'tcx>)]
+impl<'tcx> InferCtxt<'tcx> {
+    /// Given some node representing a fn-like thing in the HIR map,
+    /// returns a span and `ArgKind` information that describes the
+    /// arguments it expects. This can be supplied to
+    /// `report_arg_count_mismatch`.
+    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
+        let sm = self.tcx.sess.source_map();
+        let hir = self.tcx.hir();
+        Some(match node {
+            Node::Expr(&hir::Expr {
+                kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
+                ..
+            }) => (
+                fn_decl_span,
+                fn_arg_span,
+                hir.body(body)
+                    .params
+                    .iter()
+                    .map(|arg| {
+                        if let hir::Pat { kind: hir::PatKind::Tuple(args, _), span, .. } = *arg.pat
+                        {
+                            Some(ArgKind::Tuple(
+                                Some(span),
+                                args.iter()
+                                    .map(|pat| {
+                                        sm.span_to_snippet(pat.span)
+                                            .ok()
+                                            .map(|snippet| (snippet, "_".to_owned()))
+                                    })
+                                    .collect::<Option<Vec<_>>>()?,
+                            ))
+                        } else {
+                            let name = sm.span_to_snippet(arg.pat.span).ok()?;
+                            Some(ArgKind::Arg(name, "_".to_owned()))
+                        }
+                    })
+                    .collect::<Option<Vec<ArgKind>>>()?,
+            ),
+            Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
+            | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
+            | Node::TraitItem(&hir::TraitItem {
+                kind: hir::TraitItemKind::Fn(ref sig, _), ..
+            }) => (
+                sig.span,
+                None,
+                sig.decl
+                    .inputs
+                    .iter()
+                    .map(|arg| match arg.kind {
+                        hir::TyKind::Tup(tys) => ArgKind::Tuple(
+                            Some(arg.span),
+                            vec![("_".to_owned(), "_".to_owned()); tys.len()],
+                        ),
+                        _ => ArgKind::empty(),
+                    })
+                    .collect::<Vec<ArgKind>>(),
+            ),
+            Node::Ctor(variant_data) => {
+                let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
+                (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
+            }
+            _ => panic!("non-FnLike node found: {node:?}"),
+        })
+    }
+
+    /// Reports an error when the number of arguments needed by a
+    /// trait match doesn't match the number that the expression
+    /// provides.
+    fn report_arg_count_mismatch(
+        &self,
+        span: Span,
+        found_span: Option<Span>,
+        expected_args: Vec<ArgKind>,
+        found_args: Vec<ArgKind>,
+        is_closure: bool,
+        closure_arg_span: Option<Span>,
+    ) -> Diag<'_> {
+        let kind = if is_closure { "closure" } else { "function" };
+
+        let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
+            let arg_length = arguments.len();
+            let distinct = matches!(other, &[ArgKind::Tuple(..)]);
+            match (arg_length, arguments.get(0)) {
+                (1, Some(ArgKind::Tuple(_, fields))) => {
+                    format!("a single {}-tuple as argument", fields.len())
+                }
+                _ => format!(
+                    "{} {}argument{}",
+                    arg_length,
+                    if distinct && arg_length > 1 { "distinct " } else { "" },
+                    pluralize!(arg_length)
+                ),
+            }
+        };
+
+        let expected_str = args_str(&expected_args, &found_args);
+        let found_str = args_str(&found_args, &expected_args);
+
+        let mut err = struct_span_code_err!(
+            self.dcx(),
+            span,
+            E0593,
+            "{} is expected to take {}, but it takes {}",
+            kind,
+            expected_str,
+            found_str,
+        );
+
+        err.span_label(span, format!("expected {kind} that takes {expected_str}"));
+
+        if let Some(found_span) = found_span {
+            err.span_label(found_span, format!("takes {found_str}"));
+
+            // Suggest to take and ignore the arguments with expected_args_length `_`s if
+            // found arguments is empty (assume the user just wants to ignore args in this case).
+            // For example, if `expected_args_length` is 2, suggest `|_, _|`.
+            if found_args.is_empty() && is_closure {
+                let underscores = vec!["_"; expected_args.len()].join(", ");
+                err.span_suggestion_verbose(
+                    closure_arg_span.unwrap_or(found_span),
+                    format!(
+                        "consider changing the closure to take and ignore the expected argument{}",
+                        pluralize!(expected_args.len())
+                    ),
+                    format!("|{underscores}|"),
+                    Applicability::MachineApplicable,
+                );
+            }
+
+            if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
+                if fields.len() == expected_args.len() {
+                    let sugg = fields
+                        .iter()
+                        .map(|(name, _)| name.to_owned())
+                        .collect::<Vec<String>>()
+                        .join(", ");
+                    err.span_suggestion_verbose(
+                        found_span,
+                        "change the closure to take multiple arguments instead of a single tuple",
+                        format!("|{sugg}|"),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+            if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
+                && fields.len() == found_args.len()
+                && is_closure
+            {
+                let sugg = format!(
+                    "|({}){}|",
+                    found_args
+                        .iter()
+                        .map(|arg| match arg {
+                            ArgKind::Arg(name, _) => name.to_owned(),
+                            _ => "_".to_owned(),
+                        })
+                        .collect::<Vec<String>>()
+                        .join(", "),
+                    // add type annotations if available
+                    if found_args.iter().any(|arg| match arg {
+                        ArgKind::Arg(_, ty) => ty != "_",
+                        _ => false,
+                    }) {
+                        format!(
+                            ": ({})",
+                            fields
+                                .iter()
+                                .map(|(_, ty)| ty.to_owned())
+                                .collect::<Vec<String>>()
+                                .join(", ")
+                        )
+                    } else {
+                        String::new()
+                    },
+                );
+                err.span_suggestion_verbose(
+                    found_span,
+                    "change the closure to accept a tuple instead of individual arguments",
+                    sugg,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+
+        err
+    }
+
+    /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
+    /// in that order, and returns the generic type corresponding to the
+    /// argument of that trait (corresponding to the closure arguments).
+    fn type_implements_fn_trait(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        ty: ty::Binder<'tcx, Ty<'tcx>>,
+        polarity: ty::PredicatePolarity,
+    ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
+        self.commit_if_ok(|_| {
+            for trait_def_id in [
+                self.tcx.lang_items().fn_trait(),
+                self.tcx.lang_items().fn_mut_trait(),
+                self.tcx.lang_items().fn_once_trait(),
+            ] {
+                let Some(trait_def_id) = trait_def_id else { continue };
+                // Make a fresh inference variable so we can determine what the generic parameters
+                // of the trait are.
+                let var = self.next_ty_var(DUMMY_SP);
+                // FIXME(effects)
+                let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, [ty.skip_binder(), var]);
+                let obligation = Obligation::new(
+                    self.tcx,
+                    ObligationCause::dummy(),
+                    param_env,
+                    ty.rebind(ty::TraitPredicate { trait_ref, polarity }),
+                );
+                let ocx = ObligationCtxt::new(self);
+                ocx.register_obligation(obligation);
+                if ocx.select_all_or_error().is_empty() {
+                    return Ok((
+                        self.tcx
+                            .fn_trait_kind_from_def_id(trait_def_id)
+                            .expect("expected to map DefId to ClosureKind"),
+                        ty.rebind(self.resolve_vars_if_possible(var)),
+                    ));
+                }
+            }
+
+            Err(())
+        })
+    }
+}

compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs

@@ -0,0 +1,242 @@
+// ignore-tidy-filelength :(
+
+pub mod ambiguity;
+mod infer_ctxt_ext;
+pub mod on_unimplemented;
+pub mod suggestions;
+mod type_err_ctxt_ext;
+
+use rustc_data_structures::fx::FxIndexSet;
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_hir::intravisit::Visitor;
+use rustc_infer::traits::{Obligation, ObligationCause, ObligationCauseCode, PredicateObligation};
+use rustc_middle::ty::print::PrintTraitRefExt as _;
+use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_span::Span;
+use std::ops::ControlFlow;
+
+pub use self::infer_ctxt_ext::*;
+pub use self::type_err_ctxt_ext::*;
+
+// When outputting impl candidates, prefer showing those that are more similar.
+//
+// We also compare candidates after skipping lifetimes, which has a lower
+// priority than exact matches.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum CandidateSimilarity {
+    Exact { ignoring_lifetimes: bool },
+    Fuzzy { ignoring_lifetimes: bool },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ImplCandidate<'tcx> {
+    pub trait_ref: ty::TraitRef<'tcx>,
+    pub similarity: CandidateSimilarity,
+    impl_def_id: DefId,
+}
+
+enum GetSafeTransmuteErrorAndReason {
+    Silent,
+    Error { err_msg: String, safe_transmute_explanation: Option<String> },
+}
+
+struct UnsatisfiedConst(pub bool);
+
+/// Crude way of getting back an `Expr` from a `Span`.
+pub struct FindExprBySpan<'hir> {
+    pub span: Span,
+    pub result: Option<&'hir hir::Expr<'hir>>,
+    pub ty_result: Option<&'hir hir::Ty<'hir>>,
+    pub include_closures: bool,
+    pub tcx: TyCtxt<'hir>,
+}
+
+impl<'hir> FindExprBySpan<'hir> {
+    pub fn new(span: Span, tcx: TyCtxt<'hir>) -> Self {
+        Self { span, result: None, ty_result: None, tcx, include_closures: false }
+    }
+}
+
+impl<'v> Visitor<'v> for FindExprBySpan<'v> {
+    type NestedFilter = rustc_middle::hir::nested_filter::OnlyBodies;
+
+    fn nested_visit_map(&mut self) -> Self::Map {
+        self.tcx.hir()
+    }
+
+    fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
+        if self.span == ex.span {
+            self.result = Some(ex);
+        } else {
+            if let hir::ExprKind::Closure(..) = ex.kind
+                && self.include_closures
+                && let closure_header_sp = self.span.with_hi(ex.span.hi())
+                && closure_header_sp == ex.span
+            {
+                self.result = Some(ex);
+            }
+            hir::intravisit::walk_expr(self, ex);
+        }
+    }
+
+    fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
+        if self.span == ty.span {
+            self.ty_result = Some(ty);
+        } else {
+            hir::intravisit::walk_ty(self, ty);
+        }
+    }
+}
+
+/// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
+/// `param: ?Sized` would be a valid constraint.
+struct FindTypeParam {
+    param: rustc_span::Symbol,
+    invalid_spans: Vec<Span>,
+    nested: bool,
+}
+
+impl<'v> Visitor<'v> for FindTypeParam {
+    fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
+        // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
+    }
+
+    fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
+        // We collect the spans of all uses of the "bare" type param, like in `field: T` or
+        // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
+        // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
+        // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
+        // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
+        // in that case should make what happened clear enough.
+        match ty.kind {
+            hir::TyKind::Ptr(_) | hir::TyKind::Ref(..) | hir::TyKind::TraitObject(..) => {}
+            hir::TyKind::Path(hir::QPath::Resolved(None, path))
+                if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
+            {
+                if !self.nested {
+                    debug!(?ty, "FindTypeParam::visit_ty");
+                    self.invalid_spans.push(ty.span);
+                }
+            }
+            hir::TyKind::Path(_) => {
+                let prev = self.nested;
+                self.nested = true;
+                hir::intravisit::walk_ty(self, ty);
+                self.nested = prev;
+            }
+            _ => {
+                hir::intravisit::walk_ty(self, ty);
+            }
+        }
+    }
+}
+
+/// Summarizes information
+#[derive(Clone)]
+pub enum ArgKind {
+    /// An argument of non-tuple type. Parameters are (name, ty)
+    Arg(String, String),
+
+    /// An argument of tuple type. For a "found" argument, the span is
+    /// the location in the source of the pattern. For an "expected"
+    /// argument, it will be None. The vector is a list of (name, ty)
+    /// strings for the components of the tuple.
+    Tuple(Option<Span>, Vec<(String, String)>),
+}
+
+impl ArgKind {
+    fn empty() -> ArgKind {
+        ArgKind::Arg("_".to_owned(), "_".to_owned())
+    }
+
+    /// Creates an `ArgKind` from the expected type of an
+    /// argument. It has no name (`_`) and an optional source span.
+    pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
+        match t.kind() {
+            ty::Tuple(tys) => ArgKind::Tuple(
+                span,
+                tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
+            ),
+            _ => ArgKind::Arg("_".to_owned(), t.to_string()),
+        }
+    }
+}
+
+struct HasNumericInferVisitor;
+
+impl<'tcx> ty::TypeVisitor<TyCtxt<'tcx>> for HasNumericInferVisitor {
+    type Result = ControlFlow<()>;
+
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
+        if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
+            ControlFlow::Break(())
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+}
+
+#[derive(Copy, Clone)]
+pub enum DefIdOrName {
+    DefId(DefId),
+    Name(&'static str),
+}
+
+/// Recovers the "impl X for Y" signature from `impl_def_id` and returns it as a
+/// string.
+pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Option<String> {
+    use std::fmt::Write;
+
+    let trait_ref = tcx.impl_trait_ref(impl_def_id)?.instantiate_identity();
+    let mut w = "impl".to_owned();
+
+    let args = ty::GenericArgs::identity_for_item(tcx, impl_def_id);
+
+    // FIXME: Currently only handles ?Sized.
+    //        Needs to support ?Move and ?DynSized when they are implemented.
+    let mut types_without_default_bounds = FxIndexSet::default();
+    let sized_trait = tcx.lang_items().sized_trait();
+
+    let arg_names = args.iter().map(|k| k.to_string()).filter(|k| k != "'_").collect::<Vec<_>>();
+    if !arg_names.is_empty() {
+        types_without_default_bounds.extend(args.types());
+        w.push('<');
+        w.push_str(&arg_names.join(", "));
+        w.push('>');
+    }
+
+    write!(
+        w,
+        " {} for {}",
+        trait_ref.print_only_trait_path(),
+        tcx.type_of(impl_def_id).instantiate_identity()
+    )
+    .unwrap();
+
+    // The predicates will contain default bounds like `T: Sized`. We need to
+    // remove these bounds, and add `T: ?Sized` to any untouched type parameters.
+    let predicates = tcx.predicates_of(impl_def_id).predicates;
+    let mut pretty_predicates =
+        Vec::with_capacity(predicates.len() + types_without_default_bounds.len());
+
+    for (p, _) in predicates {
+        if let Some(poly_trait_ref) = p.as_trait_clause() {
+            if Some(poly_trait_ref.def_id()) == sized_trait {
+                // FIXME(#120456) - is `swap_remove` correct?
+                types_without_default_bounds.swap_remove(&poly_trait_ref.self_ty().skip_binder());
+                continue;
+            }
+        }
+        pretty_predicates.push(p.to_string());
+    }
+
+    pretty_predicates.extend(types_without_default_bounds.iter().map(|ty| format!("{ty}: ?Sized")));
+
+    if !pretty_predicates.is_empty() {
+        write!(w, "\n  where {}", pretty_predicates.join(", ")).unwrap();
+    }
+
+    w.push(';');
+    Some(w)
+}