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Point at return type always when type mismatch against it
Before this, the diagnostic errors would only point at the return type when changing it would be a possible solution to a type error. Add a label to the return type without a suggestion to change in order to make the source of the expected type obvious. Follow up to #42850, fixes #25133, fixes #41897.
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10 files changed

+68
-26
lines changed

10 files changed

+68
-26
lines changed

‎src/librustc/hir/map/mod.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -664,7 +664,7 @@ impl<'hir> Map<'hir> {
664664
match *node {
665665
NodeExpr(ref expr) => {
666666
match expr.node {
667-
ExprWhile(..) | ExprLoop(..) => true,
667+
ExprWhile(..) | ExprLoop(..) | ExprIf(..) => true,
668668
_ => false,
669669
}
670670
}

‎src/librustc/ty/mod.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -488,6 +488,7 @@ impl<'tcx> TyS<'tcx> {
488488
TypeVariants::TyFnPtr(..) |
489489
TypeVariants::TyDynamic(..) |
490490
TypeVariants::TyClosure(..) |
491+
TypeVariants::TyInfer(..) |
491492
TypeVariants::TyProjection(..) => false,
492493
_ => true,
493494
}

‎src/librustc_typeck/check/mod.rs

Lines changed: 35 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -4187,8 +4187,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
41874187
ty
41884188
}
41894189

4190-
/// Given a `NodeId`, return the `FnDecl` of the method it is enclosed by and whether it is
4191-
/// `fn main` if it is a method, `None` otherwise.
4190+
/// Given a `NodeId`, return the `FnDecl` of the method it is enclosed by and whether a
4191+
/// suggetion can be made, `None` otherwise.
41924192
pub fn get_fn_decl(&self, blk_id: ast::NodeId) -> Option<(hir::FnDecl, bool)> {
41934193
// Get enclosing Fn, if it is a function or a trait method, unless there's a `loop` or
41944194
// `while` before reaching it, as block tail returns are not available in them.
@@ -4199,14 +4199,23 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
41994199
name, node: hir::ItemFn(ref decl, ..), ..
42004200
}) = parent {
42014201
decl.clone().and_then(|decl| {
4202-
// This is less than ideal, it will not present the return type span on any
4203-
// method called `main`, regardless of whether it is actually the entry point.
4204-
Some((decl, name == Symbol::intern("main")))
4202+
// This is less than ideal, it will not suggest a return type span on any
4203+
// method called `main`, regardless of whether it is actually the entry point,
4204+
// but it will still present it as the reason for the expected type.
4205+
Some((decl, name != Symbol::intern("main")))
42054206
})
42064207
} else if let Node::NodeTraitItem(&hir::TraitItem {
42074208
node: hir::TraitItemKind::Method(hir::MethodSig {
42084209
ref decl, ..
42094210
}, ..), ..
4211+
}) = parent {
4212+
decl.clone().and_then(|decl| {
4213+
Some((decl, true))
4214+
})
4215+
} else if let Node::NodeImplItem(&hir::ImplItem {
4216+
node: hir::ImplItemKind::Method(hir::MethodSig {
4217+
ref decl, ..
4218+
}, ..), ..
42104219
}) = parent {
42114220
decl.clone().and_then(|decl| {
42124221
Some((decl, false))
@@ -4233,11 +4242,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
42334242
blk_id: ast::NodeId) {
42344243
self.suggest_missing_semicolon(err, expression, expected, cause_span);
42354244

4236-
if let Some((fn_decl, is_main)) = self.get_fn_decl(blk_id) {
4237-
// `fn main()` must return `()`, do not suggest changing return type
4238-
if !is_main {
4239-
self.suggest_missing_return_type(err, &fn_decl, found);
4240-
}
4245+
if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
4246+
self.suggest_missing_return_type(err, &fn_decl, expected, found, can_suggest);
42414247
}
42424248
}
42434249

@@ -4293,20 +4299,31 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
42934299
fn suggest_missing_return_type(&self,
42944300
err: &mut DiagnosticBuilder<'tcx>,
42954301
fn_decl: &hir::FnDecl,
4296-
ty: Ty<'tcx>) {
4302+
expected: Ty<'tcx>,
4303+
found: Ty<'tcx>,
4304+
can_suggest: bool) {
42974305

4298-
// Only recommend changing the return type for methods that
4306+
// Only suggest changing the return type for methods that
42994307
// haven't set a return type at all (and aren't `fn main()` or an impl).
4300-
if let &hir::FnDecl {
4301-
output: hir::FunctionRetTy::DefaultReturn(span), ..
4302-
} = fn_decl {
4303-
if ty.is_suggestable() {
4308+
match (&fn_decl.output, found.is_suggestable(), can_suggest) {
4309+
(&hir::FunctionRetTy::DefaultReturn(span), true, true) => {
43044310
err.span_suggestion(span,
43054311
"try adding a return type",
4306-
format!("-> {} ", ty));
4307-
} else {
4312+
format!("-> {} ", found));
4313+
}
4314+
(&hir::FunctionRetTy::DefaultReturn(span), false, true) => {
43084315
err.span_label(span, "possibly return type missing here?");
43094316
}
4317+
(&hir::FunctionRetTy::DefaultReturn(span), _, _) => {
4318+
// `fn main()` must return `()`, do not suggest changing return type
4319+
err.span_label(span, "expected `()` because of default return type");
4320+
}
4321+
(&hir::FunctionRetTy::Return(ref ty), _, _) => {
4322+
// Only point to return type if the expected type is the return type, as if they
4323+
// are not, the expectation must have been caused by something else.
4324+
err.span_label(ty.span,
4325+
format!("expected `{}` because of return type", expected));
4326+
}
43104327
}
43114328
}
43124329

‎src/test/compile-fail/struct-path-self-type-mismatch.rs

Lines changed: 5 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -20,17 +20,15 @@ impl Bar for Foo<i32> {
2020
}
2121

2222
impl<T> Foo<T> {
23-
fn new<U>(u: U) -> Foo<U> {
23+
fn new<U>(u: U) -> Foo<U> { //~ NOTE expected `Foo<U>` because of return type
2424
Self {
2525
//~^ ERROR mismatched types
26-
//~| expected type parameter, found a different type parameter
27-
//~| expected type `Foo<U>`
28-
//~| found type `Foo<T>`
26+
//~| NOTE expected type parameter, found a different type parameter
27+
//~| NOTE expected type `Foo<U>`
2928
inner: u
3029
//~^ ERROR mismatched types
31-
//~| expected type parameter, found a different type parameter
32-
//~| expected type `T`
33-
//~| found type `U`
30+
//~| NOTE expected type parameter, found a different type parameter
31+
//~| NOTE expected type `T`
3432
}
3533
}
3634
}

‎src/test/ui/block-result/block-must-not-have-result-res.stderr

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,8 @@
11
error[E0308]: mismatched types
22
--> $DIR/block-must-not-have-result-res.rs:15:9
33
|
4+
14 | fn drop(&mut self) {
5+
| - expected `()` because of default return type
46
15 | true //~ ERROR mismatched types
57
| ^^^^ expected (), found bool
68
|

‎src/test/ui/block-result/issue-13624.stderr

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,8 @@
11
error[E0308]: mismatched types
22
--> $DIR/issue-13624.rs:17:5
33
|
4+
16 | pub fn get_enum_struct_variant() -> () {
5+
| -- expected `()` because of return type
46
17 | Enum::EnumStructVariant { x: 1, y: 2, z: 3 }
57
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected (), found enum `a::Enum`
68
|

‎src/test/ui/block-result/issue-22645.stderr

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,9 @@ error[E0277]: the trait bound `{integer}: Scalar` is not satisfied
1111
error[E0308]: mismatched types
1212
--> $DIR/issue-22645.rs:25:3
1313
|
14+
23 | fn main() {
15+
| - expected `()` because of default return type
16+
24 | let b = Bob + 3.5;
1417
25 | b + 3 //~ ERROR E0277
1518
| ^^^^^ expected (), found struct `Bob`
1619
|

‎src/test/ui/block-result/issue-5500.stderr

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,8 @@
11
error[E0308]: mismatched types
22
--> $DIR/issue-5500.rs:12:5
33
|
4+
11 | fn main() {
5+
| - expected `()` because of default return type
46
12 | &panic!()
57
| ^^^^^^^^^ expected (), found reference
68
|

‎src/test/ui/impl-trait/equality.stderr

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,9 @@
11
error[E0308]: mismatched types
22
--> $DIR/equality.rs:25:5
33
|
4+
21 | fn two(x: bool) -> impl Foo {
5+
| -------- expected `_` because of return type
6+
...
47
25 | 0_u32
58
| ^^^^^ expected i32, found u32
69
|

‎src/test/ui/mismatched_types/abridged.stderr

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,8 @@
11
error[E0308]: mismatched types
22
--> $DIR/abridged.rs:26:5
33
|
4+
25 | fn a() -> Foo {
5+
| --- expected `Foo` because of return type
46
26 | Some(Foo { bar: 1 })
57
| ^^^^^^^^^^^^^^^^^^^^ expected struct `Foo`, found enum `std::option::Option`
68
|
@@ -10,6 +12,8 @@ error[E0308]: mismatched types
1012
error[E0308]: mismatched types
1113
--> $DIR/abridged.rs:30:5
1214
|
15+
29 | fn a2() -> Foo {
16+
| --- expected `Foo` because of return type
1317
30 | Ok(Foo { bar: 1})
1418
| ^^^^^^^^^^^^^^^^^ expected struct `Foo`, found enum `std::result::Result`
1519
|
@@ -19,6 +23,8 @@ error[E0308]: mismatched types
1923
error[E0308]: mismatched types
2024
--> $DIR/abridged.rs:34:5
2125
|
26+
33 | fn b() -> Option<Foo> {
27+
| ----------- expected `std::option::Option<Foo>` because of return type
2228
34 | Foo { bar: 1 }
2329
| ^^^^^^^^^^^^^^ expected enum `std::option::Option`, found struct `Foo`
2430
|
@@ -28,6 +34,8 @@ error[E0308]: mismatched types
2834
error[E0308]: mismatched types
2935
--> $DIR/abridged.rs:38:5
3036
|
37+
37 | fn c() -> Result<Foo, Bar> {
38+
| ---------------- expected `std::result::Result<Foo, Bar>` because of return type
3139
38 | Foo { bar: 1 }
3240
| ^^^^^^^^^^^^^^ expected enum `std::result::Result`, found struct `Foo`
3341
|
@@ -37,6 +45,9 @@ error[E0308]: mismatched types
3745
error[E0308]: mismatched types
3846
--> $DIR/abridged.rs:49:5
3947
|
48+
41 | fn d() -> X<X<String, String>, String> {
49+
| ---------------------------- expected `X<X<std::string::String, std::string::String>, std::string::String>` because of return type
50+
...
4051
49 | x
4152
| ^ expected struct `std::string::String`, found integral variable
4253
|
@@ -46,6 +57,9 @@ error[E0308]: mismatched types
4657
error[E0308]: mismatched types
4758
--> $DIR/abridged.rs:60:5
4859
|
60+
52 | fn e() -> X<X<String, String>, String> {
61+
| ---------------------------- expected `X<X<std::string::String, std::string::String>, std::string::String>` because of return type
62+
...
4963
60 | x
5064
| ^ expected struct `std::string::String`, found integral variable
5165
|

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