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Rollup merge of #95260 - compiler-errors:fn, r=davidtwco

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Better suggestions for `Fn`-family trait selection errors

1. Suppress suggestions to add `std::ops::Fn{,Mut,Once}` bounds when a type already implements `Fn{,Mut,Once}`
2. Add a note that points out that a type does in fact implement `Fn{,Mut,Once}`, but the arguments vary (either by number or by actual arguments)
3. Add a note that points out that a type does in fact implement `Fn{,Mut,Once}`, but not the right one (e.g. implements `FnMut`, but `Fn` is required).

Fixes #95147
This commit is contained in:
Matthias Krüger 2022-04-01 06:59:41 +02:00 committed by GitHub
commit 94b1960535
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GPG Key ID: 4AEE18F83AFDEB23
8 changed files with 255 additions and 9 deletions
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6
compiler/rustc_infer/src/infer/error_reporting/mod.rs
View File

@ -1091,7 +1091,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
/// Compares two given types, eliding parts that are the same between them and highlighting
/// relevant differences, and return two representation of those types for highlighted printing.
fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
pub fn cmp(
&self,
t1: Ty<'tcx>,
t2: Ty<'tcx>,
) -> (DiagnosticStyledString, DiagnosticStyledString) {
debug!("cmp(t1={}, t1.kind={:?}, t2={}, t2.kind={:?})", t1, t1.kind(), t2, t2.kind());
// helper functions

18
compiler/rustc_middle/src/ty/closure.rs
View File

@ -119,9 +119,21 @@ impl<'tcx> ClosureKind {
/// See `Ty::to_opt_closure_kind` for more details.
pub fn to_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
match self {
ty::ClosureKind::Fn => tcx.types.i8,
ty::ClosureKind::FnMut => tcx.types.i16,
ty::ClosureKind::FnOnce => tcx.types.i32,
ClosureKind::Fn => tcx.types.i8,
ClosureKind::FnMut => tcx.types.i16,
ClosureKind::FnOnce => tcx.types.i32,
}
}
pub fn from_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ClosureKind> {
if Some(def_id) == tcx.lang_items().fn_once_trait() {
Some(ClosureKind::FnOnce)
} else if Some(def_id) == tcx.lang_items().fn_mut_trait() {
Some(ClosureKind::FnMut)
} else if Some(def_id) == tcx.lang_items().fn_trait() {
Some(ClosureKind::Fn)
} else {
None
}
}
}

126
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View File

@ -2,10 +2,10 @@ pub mod on_unimplemented;
pub mod suggestions;
use super::{
EvaluationResult, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes,
Obligation, ObligationCause, ObligationCauseCode, OnUnimplementedDirective,
OnUnimplementedNote, OutputTypeParameterMismatch, Overflow, PredicateObligation,
SelectionContext, SelectionError, TraitNotObjectSafe,
EvaluationResult, FulfillmentContext, FulfillmentError, FulfillmentErrorCode,
MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
};
use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
@ -21,6 +21,8 @@ use rustc_hir::intravisit::Visitor;
use rustc_hir::GenericParam;
use rustc_hir::Item;
use rustc_hir::Node;
use rustc_infer::infer::error_reporting::same_type_modulo_infer;
use rustc_infer::traits::TraitEngine;
use rustc_middle::thir::abstract_const::NotConstEvaluatable;
use rustc_middle::traits::select::OverflowError;
use rustc_middle::ty::error::ExpectedFound;
@ -103,6 +105,17 @@ pub trait InferCtxtExt<'tcx> {
found_args: Vec<ArgKind>,
is_closure: bool,
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
/// 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>>,
constness: ty::BoundConstness,
polarity: ty::ImplPolarity,
) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
}
impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
@ -563,7 +576,64 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
}
// Try to report a help message
if !trait_ref.has_infer_types_or_consts()
if is_fn_trait
&& let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
obligation.param_env,
trait_ref.self_ty(),
trait_predicate.skip_binder().constness,
trait_predicate.skip_binder().polarity,
)
{
// If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
// suggestion to add trait bounds for the type, since we only typically implement
// these traits once.
// Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
// to implement.
let selected_kind =
ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
.expect("expected to map DefId to ClosureKind");
if !implemented_kind.extends(selected_kind) {
err.note(
&format!(
"`{}` implements `{}`, but it must implement `{}`, which is more general",
trait_ref.skip_binder().self_ty(),
implemented_kind,
selected_kind
)
);
}
// Note any argument mismatches
let given_ty = params.skip_binder();
let expected_ty = trait_ref.skip_binder().substs.type_at(1);
if let ty::Tuple(given) = given_ty.kind()
&& let ty::Tuple(expected) = expected_ty.kind()
{
if expected.len() != given.len() {
// Note number of types that were expected and given
err.note(
&format!(
"expected a closure taking {} argument{}, but one taking {} argument{} was given",
given.len(),
if given.len() == 1 { "" } else { "s" },
expected.len(),
if expected.len() == 1 { "" } else { "s" },
)
);
} else if !same_type_modulo_infer(given_ty, expected_ty) {
// Print type mismatch
let (expected_args, given_args) =
self.cmp(given_ty, expected_ty);
err.note_expected_found(
&"a closure with arguments",
expected_args,
&"a closure with arguments",
given_args,
);
}
}
} else if !trait_ref.has_infer_types_or_consts()
&& self.predicate_can_apply(obligation.param_env, trait_ref)
{
// If a where-clause may be useful, remind the
@ -1148,6 +1218,52 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
err
}
fn type_implements_fn_trait(
&self,
param_env: ty::ParamEnv<'tcx>,
ty: ty::Binder<'tcx, Ty<'tcx>>,
constness: ty::BoundConstness,
polarity: ty::ImplPolarity,
) -> 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 substitutions
// of the trait are.
let var = self.next_ty_var(TypeVariableOrigin {
span: DUMMY_SP,
kind: TypeVariableOriginKind::MiscVariable,
});
let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
let obligation = Obligation::new(
ObligationCause::dummy(),
param_env,
ty.rebind(ty::TraitPredicate {
trait_ref: ty::TraitRef::new(trait_def_id, substs),
constness,
polarity,
})
.to_predicate(self.tcx),
);
let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
fulfill_cx.register_predicate_obligation(self, obligation);
if fulfill_cx.select_all_or_error(self).is_empty() {
return Ok((
ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
.expect("expected to map DefId to ClosureKind"),
ty.rebind(self.resolve_vars_if_possible(var)),
));
}
}
Err(())
})
}
}
trait InferCtxtPrivExt<'hir, 'tcx> {

2
src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-62529-3.stderr
View File

@ -4,6 +4,8 @@ error[E0277]: expected a `Fn<(<_ as ATC<'a>>::Type,)>` closure, found `F`
LL | call(f, ());
| ^^^^ expected an `Fn<(<_ as ATC<'a>>::Type,)>` closure, found `F`
|
= note: expected a closure with arguments `((),)`
found a closure with arguments `(<_ as ATC<'a>>::Type,)`
note: required by a bound in `call`
--> $DIR/issue-62529-3.rs:9:36
|

2
src/test/ui/issues/issue-59494.stderr
View File

@ -7,6 +7,8 @@ LL | let t8 = t8n(t7, t7p(f, g));
| required by a bound introduced by this call
|
= help: the trait `Fn<(_,)>` is not implemented for `impl Fn(((_, _), _))`
= note: expected a closure with arguments `(((_, _), _),)`
found a closure with arguments `(_,)`
note: required by a bound in `t8n`
--> $DIR/issue-59494.rs:5:45
|

28
src/test/ui/trait-bounds/mismatch-fn-trait.rs Normal file
View File

@ -0,0 +1,28 @@
fn take(_f: impl FnMut(i32)) {}
fn test1(f: impl FnMut(u32)) {
take(f)
//~^ ERROR [E0277]
}
fn test2(f: impl FnMut(i32, i32)) {
take(f)
//~^ ERROR [E0277]
}
fn test3(f: impl FnMut()) {
take(f)
//~^ ERROR [E0277]
}
fn test4(f: impl FnOnce(i32)) {
take(f)
//~^ ERROR [E0277]
}
fn test5(f: impl FnOnce(u32)) {
take(f)
//~^ ERROR [E0277]
}
fn main() {}

81
src/test/ui/trait-bounds/mismatch-fn-trait.stderr Normal file
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@ -0,0 +1,81 @@
error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut(u32)`
--> $DIR/mismatch-fn-trait.rs:4:10
|
LL | take(f)
| ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut(u32)`
| |
| required by a bound introduced by this call
|
= note: expected a closure with arguments `(u32,)`
found a closure with arguments `(i32,)`
note: required by a bound in `take`
--> $DIR/mismatch-fn-trait.rs:1:18
|
LL | fn take(_f: impl FnMut(i32)) {}
| ^^^^^^^^^^ required by this bound in `take`
error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut(i32, i32)`
--> $DIR/mismatch-fn-trait.rs:9:10
|
LL | take(f)
| ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut(i32, i32)`
| |
| required by a bound introduced by this call
|
= note: expected a closure taking 2 arguments, but one taking 1 argument was given
note: required by a bound in `take`
--> $DIR/mismatch-fn-trait.rs:1:18
|
LL | fn take(_f: impl FnMut(i32)) {}
| ^^^^^^^^^^ required by this bound in `take`
error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnMut()`
--> $DIR/mismatch-fn-trait.rs:14:10
|
LL | take(f)
| ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnMut()`
| |
| required by a bound introduced by this call
|
= note: expected a closure taking 0 arguments, but one taking 1 argument was given
note: required by a bound in `take`
--> $DIR/mismatch-fn-trait.rs:1:18
|
LL | fn take(_f: impl FnMut(i32)) {}
| ^^^^^^^^^^ required by this bound in `take`
error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnOnce(i32)`
--> $DIR/mismatch-fn-trait.rs:19:10
|
LL | take(f)
| ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnOnce(i32)`
| |
| required by a bound introduced by this call
|
= note: `impl FnOnce(i32)` implements `FnOnce`, but it must implement `FnMut`, which is more general
note: required by a bound in `take`
--> $DIR/mismatch-fn-trait.rs:1:18
|
LL | fn take(_f: impl FnMut(i32)) {}
| ^^^^^^^^^^ required by this bound in `take`
error[E0277]: expected a `FnMut<(i32,)>` closure, found `impl FnOnce(u32)`
--> $DIR/mismatch-fn-trait.rs:24:10
|
LL | take(f)
| ---- ^ expected an `FnMut<(i32,)>` closure, found `impl FnOnce(u32)`
| |
| required by a bound introduced by this call
|
= note: `impl FnOnce(u32)` implements `FnOnce`, but it must implement `FnMut`, which is more general
= note: expected a closure with arguments `(u32,)`
found a closure with arguments `(i32,)`
note: required by a bound in `take`
--> $DIR/mismatch-fn-trait.rs:1:18
|
LL | fn take(_f: impl FnMut(i32)) {}
| ^^^^^^^^^^ required by this bound in `take`
error: aborting due to 5 previous errors
For more information about this error, try `rustc --explain E0277`.

1
src/test/ui/unboxed-closures/unboxed-closures-fnmut-as-fn.stderr
View File

@ -7,6 +7,7 @@ LL | let x = call_it(&S, 22);
| required by a bound introduced by this call
|
= help: the trait `Fn<(isize,)>` is not implemented for `S`
= note: `S` implements `FnMut`, but it must implement `Fn`, which is more general
note: required by a bound in `call_it`
--> $DIR/unboxed-closures-fnmut-as-fn.rs:22:14
|