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Explain type mismatch cause pointing to return type when it is impl Trait #57793

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Merged
merged 2 commits into from
Jan 24, 2019
Merged

Explain type mismatch cause pointing to return type when it is impl Trait #57793

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e33f7f7
Explain type mismatch cause pointing to return type when it is `impl …
estebank Jan 21, 2019
ab2479b
Move logic to its own method
estebank Jan 21, 2019
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29 changes: 24 additions & 5 deletions src/librustc_typeck/check/coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1199,7 +1199,6 @@ impl<'gcx, 'tcx, 'exprs, E> CoerceMany<'gcx, 'tcx, 'exprs, E>
(self.final_ty.unwrap_or(self.expected_ty), expression_ty)
};

let reason_label = "expected because of this statement";
let mut db;
match cause.code {
ObligationCauseCode::ReturnNoExpression => {
Expand Down Expand Up @@ -1244,26 +1243,46 @@ impl<'gcx, 'tcx, 'exprs, E> CoerceMany<'gcx, 'tcx, 'exprs, E>
// as prior return coercions would not be relevant (#57664).
let parent_id = fcx.tcx.hir().get_parent_node(blk_id);
let parent = fcx.tcx.hir().get(fcx.tcx.hir().get_parent_node(parent_id));
if fcx.get_node_fn_decl(parent).is_some() && !pointing_at_return_type {
if let (Some((fn_decl, _, _)), false) = (
fcx.get_node_fn_decl(parent),
pointing_at_return_type,
) {
if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
db.span_label(*sp, reason_label);
db.span_label(
fn_decl.output.span(),
"expected because this return type...",
);
db.span_label(*sp, format!(
"...is found to be `{}` here",
fcx.resolve_type_vars_with_obligations(expected),
));
}
}
}
ObligationCauseCode::ReturnType(_id) => {
db = fcx.report_mismatched_types(cause, expected, found, err);
let _id = fcx.tcx.hir().get_parent_node(_id);
let mut pointing_at_return_type = false;
let mut return_sp = None;
if let Some((fn_decl, can_suggest)) = fcx.get_fn_decl(_id) {
pointing_at_return_type = fcx.suggest_missing_return_type(
&mut db, &fn_decl, expected, found, can_suggest);
if !pointing_at_return_type {
return_sp = Some(fn_decl.output.span()); // `impl Trait` return type
}
}
if let (Some(sp), false) = (
fcx.ret_coercion_span.borrow().as_ref(),
pointing_at_return_type,
) {
if !sp.overlaps(cause.span) {
db.span_label(*sp, reason_label);
if let Some(return_sp) = return_sp {
db.span_label(return_sp, "expected because this return type...");
db.span_label( *sp, format!(
"...is found to be `{}` here",
fcx.resolve_type_vars_with_obligations(expected),
));
} else if !sp.overlaps(cause.span) {
db.span_label(*sp, "expected because of this statement");
}
}
}
Expand Down
5 changes: 4 additions & 1 deletion src/test/ui/impl-trait/equality.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,11 @@
error[E0308]: mismatched types
--> $DIR/equality.rs:15:5
|
LL | fn two(x: bool) -> impl Foo {
| -------- expected because this return type...
LL | if x {
LL | return 1_i32;
| ----- expected because of this statement
| ----- ...is found to be `i32` here
LL | }
LL | 0_u32
| ^^^^^ expected i32, found u32
Expand Down
14 changes: 11 additions & 3 deletions src/test/ui/point-to-type-err-cause-on-impl-trait-return.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,11 @@
error[E0308]: mismatched types
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:5:5
|
LL | fn foo() -> impl std::fmt::Display {
| ---------------------- expected because this return type...
LL | if false {
LL | return 0i32;
| ---- expected because of this statement
| ---- ...is found to be `i32` here
LL | }
LL | 1u32
| ^^^^ expected i32, found u32
Expand All @@ -13,8 +16,11 @@ LL | 1u32
error[E0308]: mismatched types
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:13:16
|
LL | fn bar() -> impl std::fmt::Display {
| ---------------------- expected because this return type...
LL | if false {
LL | return 0i32;
| ---- expected because of this statement
| ---- ...is found to be `i32` here
LL | } else {
LL | return 1u32;
| ^^^^ expected i32, found u32
Expand All @@ -25,10 +31,12 @@ LL | return 1u32;
error[E0308]: mismatched types
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:19:5
|
LL | fn baz() -> impl std::fmt::Display {
| ---------------------- expected because this return type...
LL | / if false {
LL | | //~^ ERROR mismatched types
LL | | return 0i32;
| | ---- expected because of this statement
| | ---- ...is found to be `i32` here
LL | | } else {
LL | | 1u32
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Mostly unrelated to this PR, but shouldn't the type mismatch span point to this 1u32 instead of the entire if expression?

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I've made a few changes recently to point at the tail expression in blocks instead of entire blocks, but haven't finished yet. This change is already in my plans :)

LL | | }
Expand Down