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Auto merge of #95758 - compiler-errors:issue-54771, r=estebank

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Only suggest removing semicolon when expression is compatible with `impl Trait`

https://github.com/rust-lang/rust/issues/54771#issuecomment-476423690
> It still needs checking that the last statement's expr can actually conform to the trait, but the naïve behavior is there.

Only suggest removing a semicolon when the type behind the semicolon actually implements the trait in an RPIT `-> impl Trait`. Also upgrade the label that suggests removing the semicolon to a suggestion (should it be verbose?).

cc #54771
This commit is contained in:
bors 2022-04-11 08:31:37 +00:00
commit d00e77078c
15 changed files with 97 additions and 32 deletions
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31
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View file

@ -1083,20 +1083,31 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
let parent_node = hir.get_parent_node(obligation.cause.body_id);
let node = hir.find(parent_node);
if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node
&& let body = hir.body(*body_id)
&& let hir::ExprKind::Block(blk, _) = &body.value.kind
&& let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind
&& sig.decl.output.span().overlaps(span)
&& blk.expr.is_none()
&& *trait_pred.self_ty().skip_binder().kind() == ty::Tuple(ty::List::empty())
// FIXME(estebank): When encountering a method with a trait
// bound not satisfied in the return type with a body that has
// no return, suggest removal of semicolon on last statement.
// Once that is added, close #54771.
&& trait_pred.self_ty().skip_binder().is_unit()
&& let Some(stmt) = blk.stmts.last()
&& let hir::StmtKind::Semi(_) = stmt.kind
&& let hir::StmtKind::Semi(expr) = stmt.kind
// Only suggest this if the expression behind the semicolon implements the predicate
&& let Some(typeck_results) = self.in_progress_typeck_results
&& let Some(ty) = typeck_results.borrow().expr_ty_opt(expr)
&& self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred, ty))
{
let sp = self.tcx.sess.source_map().end_point(stmt.span);
err.span_label(sp, "consider removing this semicolon");
err.span_label(
expr.span,
&format!(
"this expression has type `{}`, which implements `{}`",
ty,
trait_pred.print_modifiers_and_trait_path()
)
);
err.span_suggestion(
self.tcx.sess.source_map().end_point(stmt.span),
"remove this semicolon",
String::new(),
Applicability::MachineApplicable
);
return true;
}
false

2
compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
View file

@ -936,7 +936,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
} else {
err.span_suggestion_short(
span_semi,
"consider removing this semicolon",
"remove this semicolon",
String::new(),
Applicability::MachineApplicable,
);

6
src/test/ui/block-result/consider-removing-last-semi.stderr
View file

@ -7,7 +7,7 @@ LL | pub fn f() -> String {
| implicitly returns `()` as its body has no tail or `return` expression
LL | 0u8;
LL | "bla".to_string();
| - help: consider removing this semicolon
| - help: remove this semicolon
error[E0308]: mismatched types
--> $DIR/consider-removing-last-semi.rs:8:15
@ -18,7 +18,7 @@ LL | pub fn g() -> String {
| implicitly returns `()` as its body has no tail or `return` expression
LL | "this won't work".to_string();
LL | "removeme".to_string();
| - help: consider removing this semicolon
| - help: remove this semicolon
error[E0308]: mismatched types
--> $DIR/consider-removing-last-semi.rs:13:25
@ -29,7 +29,7 @@ LL | pub fn macro_tests() -> u32 {
| implicitly returns `()` as its body has no tail or `return` expression
...
LL | mac!();
| - help: consider removing this semicolon
| - help: remove this semicolon
error: aborting due to 3 previous errors

2
src/test/ui/block-result/issue-11714.stderr
View file

@ -7,7 +7,7 @@ LL | fn blah() -> i32 {
| implicitly returns `()` as its body has no tail or `return` expression
...
LL | ;
| - help: consider removing this semicolon
| - help: remove this semicolon
error: aborting due to previous error

2
src/test/ui/block-result/issue-13428.stderr
View file

@ -15,7 +15,7 @@ LL | fn bar() -> String {
| implicitly returns `()` as its body has no tail or `return` expression
LL | "foobar".to_string()
LL | ;
| - help: consider removing this semicolon
| - help: remove this semicolon
error: aborting due to 2 previous errors

2
src/test/ui/closures/old-closure-expression-remove-semicolon.fixed
View file

@ -7,6 +7,6 @@ fn foo() -> i32 {
fn main() {
let _x: i32 = {
//~^ ERROR mismatched types
foo() //~ HELP consider removing this semicolon
foo() //~ HELP remove this semicolon
};
}

2
src/test/ui/closures/old-closure-expression-remove-semicolon.rs
View file

@ -7,6 +7,6 @@ fn foo() -> i32 {
fn main() {
let _x: i32 = {
//~^ ERROR mismatched types
foo(); //~ HELP consider removing this semicolon
foo(); //~ HELP remove this semicolon
};
}

2
src/test/ui/closures/old-closure-expression-remove-semicolon.stderr
View file

@ -5,7 +5,7 @@ LL | let _x: i32 = {
| ___________________^
LL | |
LL | | foo();
| | - help: consider removing this semicolon
| | - help: remove this semicolon
LL | | };
| |_____^ expected `i32`, found `()`

4
src/test/ui/coercion/coercion-missing-tail-expected-type.stderr
View file

@ -6,7 +6,7 @@ LL | fn plus_one(x: i32) -> i32 {
| |
| implicitly returns `()` as its body has no tail or `return` expression
LL | x + 1;
| - help: consider removing this semicolon
| - help: remove this semicolon
error[E0308]: mismatched types
--> $DIR/coercion-missing-tail-expected-type.rs:8:13
@ -16,7 +16,7 @@ LL | fn foo() -> Result<u8, u64> {
| |
| implicitly returns `()` as its body has no tail or `return` expression
LL | Ok(1);
| - help: consider removing this semicolon
| - help: remove this semicolon
|
= note: expected enum `Result<u8, u64>`
found unit type `()`

2
src/test/ui/issues/issue-6458-4.stderr
View file

@ -6,7 +6,7 @@ LL | fn foo(b: bool) -> Result<bool,String> {
| |
| implicitly returns `()` as its body has no tail or `return` expression
LL | Err("bar".to_string());
| - help: consider removing this semicolon
| - help: remove this semicolon
|
= note: expected enum `Result<bool, String>`
found unit type `()`

2
src/test/ui/liveness/liveness-return-last-stmt-semi.stderr
View file

@ -14,7 +14,7 @@ LL | fn bar(x: u32) -> u32 {
| |
| implicitly returns `()` as its body has no tail or `return` expression
LL | x * 2;
| - help: consider removing this semicolon
| - help: remove this semicolon
error[E0308]: mismatched types
--> $DIR/liveness-return-last-stmt-semi.rs:13:19

21
src/test/ui/suggestions/impl-trait-return-trailing-semicolon.rs
View file

@ -1,8 +1,25 @@
trait Bar {}
impl Bar for u8 {}
impl Bar for i32 {}
struct Qux;
impl Bar for Qux {}
fn foo() -> impl Bar {
5; //~^ ERROR the trait bound `(): Bar` is not satisfied
//~^ ERROR the trait bound `(): Bar` is not satisfied
//~| ERROR the trait bound `(): Bar` is not satisfied
//~| HELP the following other types implement trait `Bar`:
5;
//~^ HELP remove this semicolon
}
fn bar() -> impl Bar {
//~^ ERROR the trait bound `(): Bar` is not satisfied
//~| ERROR the trait bound `(): Bar` is not satisfied
//~| HELP the following other types implement trait `Bar`:
//~| HELP the following other types implement trait `Bar`:
"";
}
fn main() {}

45
src/test/ui/suggestions/impl-trait-return-trailing-semicolon.stderr
View file

@ -1,23 +1,58 @@
error[E0277]: the trait bound `(): Bar` is not satisfied
--> $DIR/impl-trait-return-trailing-semicolon.rs:3:13
--> $DIR/impl-trait-return-trailing-semicolon.rs:9:13
|
LL | fn foo() -> impl Bar {
| ^^^^^^^^ the trait `Bar` is not implemented for `()`
...
LL | 5;
| - consider removing this semicolon
| -- help: remove this semicolon
| |
| this expression has type `{integer}`, which implements `Bar`
error[E0277]: the trait bound `(): Bar` is not satisfied
--> $DIR/impl-trait-return-trailing-semicolon.rs:3:22
--> $DIR/impl-trait-return-trailing-semicolon.rs:9:22
|
LL | fn foo() -> impl Bar {
| ______________________^
LL | |
LL | |
LL | |
LL | | 5;
LL | |
LL | | }
| |_^ the trait `Bar` is not implemented for `()`
|
= help: the trait `Bar` is implemented for `u8`
= help: the following other types implement trait `Bar`:
Qux
i32
error: aborting due to 2 previous errors
error[E0277]: the trait bound `(): Bar` is not satisfied
--> $DIR/impl-trait-return-trailing-semicolon.rs:17:13
|
LL | fn bar() -> impl Bar {
| ^^^^^^^^ the trait `Bar` is not implemented for `()`
|
= help: the following other types implement trait `Bar`:
Qux
i32
error[E0277]: the trait bound `(): Bar` is not satisfied
--> $DIR/impl-trait-return-trailing-semicolon.rs:17:22
|
LL | fn bar() -> impl Bar {
| ______________________^
LL | |
LL | |
LL | |
LL | |
LL | | "";
LL | | }
| |_^ the trait `Bar` is not implemented for `()`
|
= help: the following other types implement trait `Bar`:
Qux
i32
error: aborting due to 4 previous errors
For more information about this error, try `rustc --explain E0277`.

4
src/test/ui/suggestions/issue-81098.stderr
View file

@ -27,7 +27,9 @@ LL | fn ok() -> impl core::fmt::Display {
| ^^^^^^^^^^^^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
LL |
LL | 1;
| - consider removing this semicolon
| -- help: remove this semicolon
| |
| this expression has type `{integer}`, which implements `std::fmt::Display`
|
= help: the trait `std::fmt::Display` is not implemented for `()`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead

2
src/test/ui/suggestions/match-with-different-arm-types-as-stmt-instead-of-expr.stderr
View file

@ -7,7 +7,7 @@ LL | fn not_all_paths(a: &str) -> u32 {
| implicitly returns `()` as its body has no tail or `return` expression
...
LL | };
| - help: consider removing this semicolon
| - help: remove this semicolon
error[E0308]: `match` arms have incompatible types
--> $DIR/match-with-different-arm-types-as-stmt-instead-of-expr.rs:26:14