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Rollup merge of #108930 - Ezrashaw:better-error-for-manual-fn-impl, r…
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…=petrochenkov

feat: implement better error for manual impl of `Fn*` traits

Fixes #39259

cc `@estebank` (you gave me some advice in the linked issue, would you like to review?)
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matthiaskrgr authored Mar 10, 2023
2 parents 4ad3230 + a30c2c2 commit 7699462
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Showing 10 changed files with 142 additions and 51 deletions.
3 changes: 3 additions & 0 deletions compiler/rustc_hir_analysis/locales/en-US.ftl
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,9 @@ hir_analysis_assoc_type_binding_not_allowed =
associated type bindings are not allowed here
.label = associated type not allowed here
hir_analysis_parenthesized_fn_trait_expansion =
parenthesized trait syntax expands to `{$expanded_type}`
hir_analysis_typeof_reserved_keyword_used =
`typeof` is a reserved keyword but unimplemented
.suggestion = consider replacing `typeof(...)` with an actual type
Expand Down
107 changes: 72 additions & 35 deletions compiler/rustc_hir_analysis/src/astconv/errors.rs
Original file line number Diff line number Diff line change
@@ -1,10 +1,14 @@
use crate::astconv::AstConv;
use crate::errors::{ManualImplementation, MissingTypeParams};
use crate::errors::{
AssocTypeBindingNotAllowed, ManualImplementation, MissingTypeParams,
ParenthesizedFnTraitExpansion,
};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, ErrorGuaranteed};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_infer::traits::FulfillmentError;
use rustc_middle::ty::TyCtxt;
use rustc_middle::ty::{self, Ty};
use rustc_session::parse::feature_err;
use rustc_span::edit_distance::find_best_match_for_name;
Expand Down Expand Up @@ -78,43 +82,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
// Do not suggest the other syntax if we are in trait impl:
// the desugaring would contain an associated type constraint.
if !is_impl {
let args = trait_segment
.args
.as_ref()
.and_then(|args| args.args.get(0))
.and_then(|arg| match arg {
hir::GenericArg::Type(ty) => match ty.kind {
hir::TyKind::Tup(t) => t
.iter()
.map(|e| sess.source_map().span_to_snippet(e.span))
.collect::<Result<Vec<_>, _>>()
.map(|a| a.join(", ")),
_ => sess.source_map().span_to_snippet(ty.span),
}
.map(|s| format!("({})", s))
.ok(),
_ => None,
})
.unwrap_or_else(|| "()".to_string());
let ret = trait_segment
.args()
.bindings
.iter()
.find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
(true, hir::TypeBindingKind::Equality { term }) => {
let span = match term {
hir::Term::Ty(ty) => ty.span,
hir::Term::Const(c) => self.tcx().hir().span(c.hir_id),
};
sess.source_map().span_to_snippet(span).ok()
}
_ => None,
})
.unwrap_or_else(|| "()".to_string());
err.span_suggestion(
span,
"use parenthetical notation instead",
format!("{}{} -> {}", trait_segment.ident, args, ret),
fn_trait_to_string(self.tcx(), trait_segment, true),
Applicability::MaybeIncorrect,
);
}
Expand Down Expand Up @@ -629,3 +600,69 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
err.emit();
}
}

/// Emits an error regarding forbidden type binding associations
pub fn prohibit_assoc_ty_binding(
tcx: TyCtxt<'_>,
span: Span,
segment: Option<(&hir::PathSegment<'_>, Span)>,
) {
tcx.sess.emit_err(AssocTypeBindingNotAllowed { span, fn_trait_expansion: if let Some((segment, span)) = segment && segment.args().parenthesized {
Some(ParenthesizedFnTraitExpansion { span, expanded_type: fn_trait_to_string(tcx, segment, false) })
} else {
None
}});
}

pub(crate) fn fn_trait_to_string(
tcx: TyCtxt<'_>,
trait_segment: &hir::PathSegment<'_>,
parenthesized: bool,
) -> String {
let args = trait_segment
.args
.as_ref()
.and_then(|args| args.args.get(0))
.and_then(|arg| match arg {
hir::GenericArg::Type(ty) => match ty.kind {
hir::TyKind::Tup(t) => t
.iter()
.map(|e| tcx.sess.source_map().span_to_snippet(e.span))
.collect::<Result<Vec<_>, _>>()
.map(|a| a.join(", ")),
_ => tcx.sess.source_map().span_to_snippet(ty.span),
}
.map(|s| {
// `s.empty()` checks to see if the type is the unit tuple, if so we don't want a comma
if parenthesized || s.is_empty() { format!("({})", s) } else { format!("({},)", s) }
})
.ok(),
_ => None,
})
.unwrap_or_else(|| "()".to_string());

let ret = trait_segment
.args()
.bindings
.iter()
.find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
(true, hir::TypeBindingKind::Equality { term }) => {
let span = match term {
hir::Term::Ty(ty) => ty.span,
hir::Term::Const(c) => tcx.hir().span(c.hir_id),
};

(span != tcx.hir().span(trait_segment.hir_id))
.then_some(tcx.sess.source_map().span_to_snippet(span).ok())
.flatten()
}
_ => None,
})
.unwrap_or_else(|| "()".to_string());

if parenthesized {
format!("{}{} -> {}", trait_segment.ident, args, ret)
} else {
format!("{}<{}, Output={}>", trait_segment.ident, args, ret)
}
}
12 changes: 3 additions & 9 deletions compiler/rustc_hir_analysis/src/astconv/generics.rs
Original file line number Diff line number Diff line change
@@ -1,9 +1,8 @@
use super::IsMethodCall;
use crate::astconv::{
CreateSubstsForGenericArgsCtxt, ExplicitLateBound, GenericArgCountMismatch,
GenericArgCountResult, GenericArgPosition,
errors::prohibit_assoc_ty_binding, CreateSubstsForGenericArgsCtxt, ExplicitLateBound,
GenericArgCountMismatch, GenericArgCountResult, GenericArgPosition,
};
use crate::errors::AssocTypeBindingNotAllowed;
use crate::structured_errors::{GenericArgsInfo, StructuredDiagnostic, WrongNumberOfGenericArgs};
use rustc_ast::ast::ParamKindOrd;
use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
Expand Down Expand Up @@ -433,7 +432,7 @@ pub(crate) fn check_generic_arg_count(
(gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();

if gen_pos != GenericArgPosition::Type && let Some(b) = gen_args.bindings.first() {
prohibit_assoc_ty_binding(tcx, b.span);
prohibit_assoc_ty_binding(tcx, b.span, None);
}

let explicit_late_bound =
Expand Down Expand Up @@ -589,11 +588,6 @@ pub(crate) fn check_generic_arg_count(
}
}

/// Emits an error regarding forbidden type binding associations
pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
tcx.sess.emit_err(AssocTypeBindingNotAllowed { span });
}

/// Prohibits explicit lifetime arguments if late-bound lifetime parameters
/// are present. This is used both for datatypes and function calls.
pub(crate) fn prohibit_explicit_late_bound_lifetimes(
Expand Down
13 changes: 6 additions & 7 deletions compiler/rustc_hir_analysis/src/astconv/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5,9 +5,8 @@
mod errors;
pub mod generics;

use crate::astconv::generics::{
check_generic_arg_count, create_substs_for_generic_args, prohibit_assoc_ty_binding,
};
use crate::astconv::errors::prohibit_assoc_ty_binding;
use crate::astconv::generics::{check_generic_arg_count, create_substs_for_generic_args};
use crate::bounds::Bounds;
use crate::collect::HirPlaceholderCollector;
use crate::errors::{
Expand Down Expand Up @@ -295,7 +294,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
ty::BoundConstness::NotConst,
);
if let Some(b) = item_segment.args().bindings.first() {
prohibit_assoc_ty_binding(self.tcx(), b.span);
prohibit_assoc_ty_binding(self.tcx(), b.span, Some((item_segment, span)));
}

substs
Expand Down Expand Up @@ -631,7 +630,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
);

if let Some(b) = item_segment.args().bindings.first() {
prohibit_assoc_ty_binding(self.tcx(), b.span);
prohibit_assoc_ty_binding(self.tcx(), b.span, Some((item_segment, span)));
}

args
Expand Down Expand Up @@ -825,7 +824,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
constness,
);
if let Some(b) = trait_segment.args().bindings.first() {
prohibit_assoc_ty_binding(self.tcx(), b.span);
prohibit_assoc_ty_binding(self.tcx(), b.span, Some((trait_segment, span)));
}
self.tcx().mk_trait_ref(trait_def_id, substs)
}
Expand Down Expand Up @@ -2596,7 +2595,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
for segment in segments {
// Only emit the first error to avoid overloading the user with error messages.
if let Some(b) = segment.args().bindings.first() {
prohibit_assoc_ty_binding(self.tcx(), b.span);
prohibit_assoc_ty_binding(self.tcx(), b.span, None);
return true;
}
}
Expand Down
12 changes: 12 additions & 0 deletions compiler/rustc_hir_analysis/src/errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,18 @@ pub struct AssocTypeBindingNotAllowed {
#[primary_span]
#[label]
pub span: Span,

#[subdiagnostic]
pub fn_trait_expansion: Option<ParenthesizedFnTraitExpansion>,
}

#[derive(Subdiagnostic)]
#[help(hir_analysis_parenthesized_fn_trait_expansion)]
pub struct ParenthesizedFnTraitExpansion {
#[primary_span]
pub span: Span,

pub expanded_type: String,
}

#[derive(Diagnostic)]
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,12 @@ error[E0229]: associated type bindings are not allowed here
|
LL | impl FnOnce() for Foo1 {
| ^^^^^^^^ associated type not allowed here
|
help: parenthesized trait syntax expands to `FnOnce<(), Output=()>`
--> $DIR/feature-gate-unboxed-closures-manual-impls.rs:16:6
|
LL | impl FnOnce() for Foo1 {
| ^^^^^^^^

error[E0658]: the precise format of `Fn`-family traits' type parameters is subject to change
--> $DIR/feature-gate-unboxed-closures-manual-impls.rs:23:6
Expand Down
13 changes: 13 additions & 0 deletions tests/ui/fn/issue-39259.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
#![feature(fn_traits)]
#![feature(unboxed_closures)]

struct S;

impl Fn(u32) -> u32 for S {
//~^ ERROR associated type bindings are not allowed here [E0229]
fn call(&self) -> u32 {
5
}
}

fn main() {}
15 changes: 15 additions & 0 deletions tests/ui/fn/issue-39259.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
error[E0229]: associated type bindings are not allowed here
--> $DIR/issue-39259.rs:6:17
|
LL | impl Fn(u32) -> u32 for S {
| ^^^ associated type not allowed here
|
help: parenthesized trait syntax expands to `Fn<(u32,), Output=u32>`
--> $DIR/issue-39259.rs:6:6
|
LL | impl Fn(u32) -> u32 for S {
| ^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0229`.
6 changes: 6 additions & 0 deletions tests/ui/lifetimes/issue-95023.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,12 @@ error[E0229]: associated type bindings are not allowed here
|
LL | impl Fn(&isize) for Error {
| ^^^^^^^^^^ associated type not allowed here
|
help: parenthesized trait syntax expands to `Fn<(&isize,), Output=()>`
--> $DIR/issue-95023.rs:3:6
|
LL | impl Fn(&isize) for Error {
| ^^^^^^^^^^

error[E0220]: associated type `B` not found for `Self`
--> $DIR/issue-95023.rs:6:44
Expand Down
6 changes: 6 additions & 0 deletions tests/ui/traits/issue-87558.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,12 @@ error[E0229]: associated type bindings are not allowed here
|
LL | impl Fn(&isize) for Error {
| ^^^^^^^^^^ associated type not allowed here
|
help: parenthesized trait syntax expands to `Fn<(&isize,), Output=()>`
--> $DIR/issue-87558.rs:3:6
|
LL | impl Fn(&isize) for Error {
| ^^^^^^^^^^

error: aborting due to 3 previous errors

Expand Down

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