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On incorrect equality constraint likely to be assoc type, suggest appropriate syntax

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When encountering `where <A as Foo>::Bar = B`, it is possible that `Bar`
is an associated type. If so, suggest `where A: Foo<Bar = B>`.

CC #20041.
This commit is contained in:
Esteban Küber 2020-04-08 11:10:16 -07:00
parent 3453db7bfc
commit d8d02f8f18
4 changed files with 134 additions and 12 deletions
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94
src/librustc_ast_passes/ast_validation.rs
View File

@ -23,6 +23,7 @@ use rustc_session::Session;
use rustc_span::symbol::{kw, sym};
use rustc_span::Span;
use std::mem;
use std::ops::DerefMut;
const MORE_EXTERN: &str =
"for more information, visit https://doc.rust-lang.org/std/keyword.extern.html";
@ -1113,17 +1114,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
for predicate in &generics.where_clause.predicates {
if let WherePredicate::EqPredicate(ref predicate) = *predicate {
self.err_handler()
.struct_span_err(
predicate.span,
"equality constraints are not yet supported in `where` clauses",
)
.span_label(predicate.span, "not supported")
.note(
"see issue #20041 <https://github.com/rust-lang/rust/issues/20041> \
for more information",
)
.emit();
deny_equality_constraints(self, predicate, generics);
}
}
@ -1300,6 +1291,87 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
}
}
fn deny_equality_constraints(
this: &mut AstValidator<'_>,
predicate: &WhereEqPredicate,
generics: &Generics,
) {
let mut err = this.err_handler().struct_span_err(
predicate.span,
"equality constraints are not yet supported in `where` clauses",
);
err.span_label(predicate.span, "not supported");
// Given `<A as Foo>::Bar = RhsTy`, suggest `A: Foo<Bar = RhsTy>`.
if let TyKind::Path(Some(qself), full_path) = &predicate.lhs_ty.kind {
if let TyKind::Path(None, path) = &qself.ty.kind {
match &path.segments[..] {
[PathSegment { ident, args: None, .. }] => {
for param in &generics.params {
if param.ident == *ident {
let param = ident;
match &full_path.segments[qself.position..] {
[PathSegment { ident, .. }] => {
// Make a new `Path` from `foo::Bar` to `Foo<Bar = RhsTy>`.
let mut assoc_path = full_path.clone();
// Remove `Bar` from `Foo::Bar`.
assoc_path.segments.pop();
let len = assoc_path.segments.len() - 1;
// Build `<Bar = RhsTy>`.
let arg = AngleBracketedArg::Constraint(AssocTyConstraint {
id: rustc_ast::node_id::DUMMY_NODE_ID,
ident: *ident,
kind: AssocTyConstraintKind::Equality {
ty: predicate.rhs_ty.clone(),
},
span: ident.span,
});
// Add `<Bar = RhsTy>` to `Foo`.
match &mut assoc_path.segments[len].args {
Some(args) => match args.deref_mut() {
GenericArgs::Parenthesized(_) => continue,
GenericArgs::AngleBracketed(args) => {
args.args.push(arg);
}
},
empty_args => {
*empty_args = AngleBracketedArgs {
span: ident.span,
args: vec![arg],
}
.into();
}
}
err.span_suggestion_verbose(
predicate.span,
&format!(
"if `{}` is an associated type you're trying to set, \
use the associated type binding syntax",
ident
),
format!(
"{}: {}",
param,
pprust::path_to_string(&assoc_path)
),
Applicability::MaybeIncorrect,
);
}
_ => {}
};
}
}
}
_ => {}
}
}
}
err.note(
"see issue #20041 <https://github.com/rust-lang/rust/issues/20041> for more information",
);
err.emit();
}
pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) -> bool {
let mut validator = AstValidator {
session,

11
src/test/ui/generic-associated-types/missing-bounds.fixed
View File

@ -32,4 +32,15 @@ impl<B: std::ops::Add<Output = B>> Add for D<B> {
}
}
struct E<B>(B);
impl<B: Add> Add for E<B> where B: Add<Output = B>, B: std::ops::Add<Output = B> {
//~^ ERROR equality constraints are not yet supported in `where` clauses
type Output = Self;
fn add(self, rhs: Self) -> Self {
Self(self.0 + rhs.0) //~ ERROR mismatched types
}
}
fn main() {}

11
src/test/ui/generic-associated-types/missing-bounds.rs
View File

@ -32,4 +32,15 @@ impl<B> Add for D<B> {
}
}
struct E<B>(B);
impl<B: Add> Add for E<B> where <B as Add>::Output = B {
//~^ ERROR equality constraints are not yet supported in `where` clauses
type Output = Self;
fn add(self, rhs: Self) -> Self {
Self(self.0 + rhs.0) //~ ERROR mismatched types
}
}
fn main() {}

30
src/test/ui/generic-associated-types/missing-bounds.stderr
View File

@ -1,3 +1,15 @@
error: equality constraints are not yet supported in `where` clauses
--> $DIR/missing-bounds.rs:37:33
|
LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
| ^^^^^^^^^^^^^^^^^^^^^^ not supported
|
= note: see issue #20041 <https://github.com/rust-lang/rust/issues/20041> for more information
help: if `Output` is an associated type you're trying to set, use the associated type binding syntax
|
LL | impl<B: Add> Add for E<B> where B: Add<Output = B> {
| ^^^^^^^^^^^^^^^^^^
error[E0308]: mismatched types
--> $DIR/missing-bounds.rs:11:11
|
@ -43,7 +55,23 @@ help: consider restricting type parameter `B`
LL | impl<B: std::ops::Add<Output = B>> Add for D<B> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 3 previous errors
error[E0308]: mismatched types
--> $DIR/missing-bounds.rs:42:14
|
LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
| - this type parameter
...
LL | Self(self.0 + rhs.0)
| ^^^^^^^^^^^^^^ expected type parameter `B`, found associated type
|
= note: expected type parameter `B`
found associated type `<B as std::ops::Add>::Output`
help: consider further restricting type parameter `B`
|
LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B, B: std::ops::Add<Output = B> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 5 previous errors
Some errors have detailed explanations: E0308, E0369.
For more information about an error, try `rustc --explain E0308`.