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Rollup merge of #92806 - compiler-errors:better-impl-trait-deny, r=estebank

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Add more information to `impl Trait` error

Fixes #92458

Let me know if I went overboard here, or if the suggestions could use some refinement.

r? `@estebank`
Feel free to reassign to someone else
This commit is contained in:
Matthias Krüger
2022-02-18 23:23:04 +01:00
committed by GitHub
parent 0bb72a2c66 207fb5f070
commit 5c08c39121
36 changed files with 366 additions and 216 deletions
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128
compiler/rustc_ast_lowering/src/lib.rs
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@@ -256,19 +256,28 @@ enum ImplTraitContext<'b, 'a> {
/// Position in which `impl Trait` is disallowed.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
enum ImplTraitPosition {
/// Disallowed in `let` / `const` / `static` bindings.
Binding,
/// All other positions.
Other,
Path,
Variable,
Type,
Trait,
AsyncBlock,
Bound,
Generic,
ExternFnParam,
ClosureParam,
PointerParam,
FnTraitParam,
TraitParam,
ImplParam,
ExternFnReturn,
ClosureReturn,
PointerReturn,
FnTraitReturn,
TraitReturn,
ImplReturn,
}
impl<'a> ImplTraitContext<'_, 'a> {
#[inline]
fn disallowed() -> Self {
ImplTraitContext::Disallowed(ImplTraitPosition::Other)
}
fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
use self::ImplTraitContext::*;
match self {
@@ -284,6 +293,54 @@ impl<'a> ImplTraitContext<'_, 'a> {
}
}
impl std::fmt::Display for ImplTraitPosition {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let name = match self {
ImplTraitPosition::Path => "path",
ImplTraitPosition::Variable => "variable binding",
ImplTraitPosition::Type => "type",
ImplTraitPosition::Trait => "trait",
ImplTraitPosition::AsyncBlock => "async block",
ImplTraitPosition::Bound => "bound",
ImplTraitPosition::Generic => "generic",
ImplTraitPosition::ExternFnParam => "`extern fn` param",
ImplTraitPosition::ClosureParam => "closure param",
ImplTraitPosition::PointerParam => "`fn` pointer param",
ImplTraitPosition::FnTraitParam => "`Fn` trait param",
ImplTraitPosition::TraitParam => "trait method param",
ImplTraitPosition::ImplParam => "`impl` method param",
ImplTraitPosition::ExternFnReturn => "`extern fn` return",
ImplTraitPosition::ClosureReturn => "closure return",
ImplTraitPosition::PointerReturn => "`fn` pointer return",
ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
ImplTraitPosition::TraitReturn => "trait method return",
ImplTraitPosition::ImplReturn => "`impl` method return",
};
write!(f, "{}", name)
}
}
#[derive(Debug)]
enum FnDeclKind {
Fn,
Inherent,
ExternFn,
Closure,
Pointer,
Trait,
Impl,
}
impl FnDeclKind {
fn impl_trait_return_allowed(&self) -> bool {
match self {
FnDeclKind::Fn | FnDeclKind::Inherent => true,
_ => false,
}
}
}
pub fn lower_crate<'a, 'hir>(
sess: &'a Session,
krate: &'a Crate,
@@ -1232,11 +1289,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
generic_params: this.lower_generic_params(
&f.generic_params,
ImplTraitContext::disallowed(),
ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
),
unsafety: this.lower_unsafety(f.unsafety),
abi: this.lower_extern(f.ext),
decl: this.lower_fn_decl(&f.decl, None, false, None),
decl: this.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
param_names: this.lower_fn_params_to_names(&f.decl),
}))
})
@@ -1357,13 +1414,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
}),
))
}
ImplTraitContext::Disallowed(_) => {
ImplTraitContext::Disallowed(position) => {
let mut err = struct_span_err!(
self.sess,
t.span,
E0562,
"`impl Trait` not allowed outside of {}",
"function and method return types",
"`impl Trait` only allowed in function and inherent method return types, not in {}",
position
);
err.emit();
hir::TyKind::Err
@@ -1528,16 +1585,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
&mut self,
decl: &FnDecl,
mut in_band_ty_params: Option<(LocalDefId, &mut Vec<hir::GenericParam<'hir>>)>,
impl_trait_return_allow: bool,
kind: FnDeclKind,
make_ret_async: Option<NodeId>,
) -> &'hir hir::FnDecl<'hir> {
debug!(
"lower_fn_decl(\
fn_decl: {:?}, \
in_band_ty_params: {:?}, \
impl_trait_return_allow: {}, \
kind: {:?}, \
make_ret_async: {:?})",
decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
decl, in_band_ty_params, kind, make_ret_async,
);
let lt_mode = if make_ret_async.is_some() {
// In `async fn`, argument-position elided lifetimes
@@ -1567,7 +1624,19 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
ImplTraitContext::Universal(ibty, this.current_hir_id_owner),
)
} else {
this.lower_ty_direct(&param.ty, ImplTraitContext::disallowed())
this.lower_ty_direct(
&param.ty,
ImplTraitContext::Disallowed(match kind {
FnDeclKind::Fn | FnDeclKind::Inherent => {
unreachable!("fn should allow in-band lifetimes")
}
FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
FnDeclKind::Trait => ImplTraitPosition::TraitParam,
FnDeclKind::Impl => ImplTraitPosition::ImplParam,
}),
)
}
}))
});
@@ -1582,13 +1651,22 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
match decl.output {
FnRetTy::Ty(ref ty) => {
let context = match in_band_ty_params {
Some((def_id, _)) if impl_trait_return_allow => {
Some((def_id, _)) if kind.impl_trait_return_allowed() => {
ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id: def_id,
origin: hir::OpaqueTyOrigin::FnReturn(def_id),
}
}
_ => ImplTraitContext::disallowed(),
_ => ImplTraitContext::Disallowed(match kind {
FnDeclKind::Fn | FnDeclKind::Inherent => {
unreachable!("fn should allow in-band lifetimes")
}
FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
}),
};
hir::FnRetTy::Return(self.lower_ty(ty, context))
}
@@ -1946,7 +2024,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
GenericParamKind::Type { ref default, .. } => {
let kind = hir::GenericParamKind::Type {
default: default.as_ref().map(|x| {
self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Other))
self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Type))
}),
synthetic: false,
};
@@ -1954,9 +2032,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
(hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
}
GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
let ty = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_ty(&ty, ImplTraitContext::disallowed())
let ty =
self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type))
});
let default = default.as_ref().map(|def| self.lower_anon_const(def));
(