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Rollup merge of #120261 - estebank:issue-102629, r=wesleywiser

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Provide structured suggestion to use trait objects in some cases of `if` arm type divergence

```
error[E0308]: `if` and `else` have incompatible types
  --> $DIR/suggest-box-on-divergent-if-else-arms.rs:15:9
   |
LL |       let _ = if true {
   |  _____________-
LL | |         Struct
   | |         ------ expected because of this
LL | |     } else {
LL | |         foo()
   | |         ^^^^^ expected `Struct`, found `Box<dyn Trait>`
LL | |     };
   | |_____- `if` and `else` have incompatible types
   |
   = note: expected struct `Struct`
              found struct `Box<dyn Trait>`
help: `Struct` implements `Trait` so you can box it to coerce to the trait object `Box<dyn Trait>`
   |
LL |         Box::new(Struct)
   |         +++++++++      +

error[E0308]: `if` and `else` have incompatible types
  --> $DIR/suggest-box-on-divergent-if-else-arms.rs:20:9
   |
LL |       let _ = if true {
   |  _____________-
LL | |         foo()
   | |         ----- expected because of this
LL | |     } else {
LL | |         Struct
   | |         ^^^^^^ expected `Box<dyn Trait>`, found `Struct`
LL | |     };
   | |_____- `if` and `else` have incompatible types
   |
   = note: expected struct `Box<dyn Trait>`
              found struct `Struct`
   = note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html
help: store this in the heap by calling `Box::new`
   |
LL |         Box::new(Struct)
   |         +++++++++      +

error[E0308]: `if` and `else` have incompatible types
  --> $DIR/suggest-box-on-divergent-if-else-arms.rs:25:9
   |
LL |   fn bar() -> impl Trait {
   |               ---------- the found opaque type
...
LL |       let _ = if true {
   |  _____________-
LL | |         Struct
   | |         ------ expected because of this
LL | |     } else {
LL | |         bar()
   | |         ^^^^^ expected `Struct`, found opaque type
LL | |     };
   | |_____- `if` and `else` have incompatible types
   |
   = note:   expected struct `Struct`
           found opaque type `impl Trait`
help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box<dyn Trait>`
   |
LL ~         Box::new(Struct) as Box<dyn Trait>
LL |     } else {
LL ~         Box::new(bar())
   |

error[E0308]: `if` and `else` have incompatible types
  --> $DIR/suggest-box-on-divergent-if-else-arms.rs:30:9
   |
LL |   fn bar() -> impl Trait {
   |               ---------- the expected opaque type
...
LL |       let _ = if true {
   |  _____________-
LL | |         bar()
   | |         ----- expected because of this
LL | |     } else {
LL | |         Struct
   | |         ^^^^^^ expected opaque type, found `Struct`
LL | |     };
   | |_____- `if` and `else` have incompatible types
   |
   = note: expected opaque type `impl Trait`
                   found struct `Struct`
help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box<dyn Trait>`
   |
LL ~         Box::new(bar()) as Box<dyn Trait>
LL |     } else {
LL ~         Box::new(Struct)
   |
```

Partially address #102629.
This commit is contained in:
León Orell Valerian Liehr 2024-01-23 21:53:59 +01:00 committed by GitHub
commit 3f2f8eee02
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
5 changed files with 267 additions and 17 deletions
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8
compiler/rustc_hir_typeck/src/demand.rs
View File

@ -44,7 +44,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
|| self.suggest_non_zero_new_unwrap(err, expr, expected, expr_ty)
|| self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty)
|| self.suggest_no_capture_closure(err, expected, expr_ty)
|| self.suggest_boxing_when_appropriate(err, expr.span, expr.hir_id, expected, expr_ty)
|| self.suggest_boxing_when_appropriate(
err,
expr.peel_blocks().span,
expr.hir_id,
expected,
expr_ty,
)
|| self.suggest_block_to_brackets_peeling_refs(err, expr, expr_ty, expected)
|| self.suggest_copied_cloned_or_as_ref(err, expr, expr_ty, expected)
|| self.suggest_clone_for_ref(err, expr, expr_ty, expected)

118
compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
View File

@ -294,8 +294,9 @@ impl<T> Trait<T> for X {
);
}
}
(ty::Alias(ty::Opaque, alias), _) | (_, ty::Alias(ty::Opaque, alias))
if alias.def_id.is_local()
(_, ty::Alias(ty::Opaque, opaque_ty))
| (ty::Alias(ty::Opaque, opaque_ty), _) => {
if opaque_ty.def_id.is_local()
&& matches!(
tcx.def_kind(body_owner_def_id),
DefKind::Fn
@ -303,21 +304,74 @@ impl<T> Trait<T> for X {
| DefKind::Const
| DefKind::AssocFn
| DefKind::AssocConst
) =>
{
if tcx.is_type_alias_impl_trait(alias.def_id) {
if !tcx
)
&& tcx.is_type_alias_impl_trait(opaque_ty.def_id)
&& !tcx
.opaque_types_defined_by(body_owner_def_id.expect_local())
.contains(&alias.def_id.expect_local())
{
let sp = tcx
.def_ident_span(body_owner_def_id)
.unwrap_or_else(|| tcx.def_span(body_owner_def_id));
diag.span_note(
sp,
"\
this item must have the opaque type in its signature \
in order to be able to register hidden types",
.contains(&opaque_ty.def_id.expect_local())
{
let sp = tcx
.def_ident_span(body_owner_def_id)
.unwrap_or_else(|| tcx.def_span(body_owner_def_id));
diag.span_note(
sp,
"this item must have the opaque type in its signature in order to \
be able to register hidden types",
);
}
// If two if arms can be coerced to a trait object, provide a structured
// suggestion.
let ObligationCauseCode::IfExpression(cause) = cause.code() else {
return;
};
let hir::Node::Block(blk) = self.tcx.hir_node(cause.then_id) else {
return;
};
let Some(then) = blk.expr else {
return;
};
let hir::Node::Block(blk) = self.tcx.hir_node(cause.else_id) else {
return;
};
let Some(else_) = blk.expr else {
return;
};
let expected = match values.found.kind() {
ty::Alias(..) => values.expected,
_ => values.found,
};
let preds = tcx.explicit_item_bounds(opaque_ty.def_id);
for (pred, _span) in preds.skip_binder() {
let ty::ClauseKind::Trait(trait_predicate) = pred.kind().skip_binder()
else {
continue;
};
if trait_predicate.polarity != ty::ImplPolarity::Positive {
continue;
}
let def_id = trait_predicate.def_id();
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, expected, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let trait_name = tcx.item_name(def_id);
diag.multipart_suggestion(
format!(
"`{expected}` implements `{trait_name}` so you can box \
both arms and coerce to the trait object \
`Box<dyn {trait_name}>`",
),
vec![
(then.span.shrink_to_lo(), "Box::new(".to_string()),
(
then.span.shrink_to_hi(),
format!(") as Box<dyn {}>", tcx.def_path_str(def_id)),
),
(else_.span.shrink_to_lo(), "Box::new(".to_string()),
(else_.span.shrink_to_hi(), ")".to_string()),
],
MachineApplicable,
);
}
}
@ -330,6 +384,38 @@ impl<T> Trait<T> for X {
);
}
}
(ty::Adt(_, _), ty::Adt(def, args))
if let ObligationCauseCode::IfExpression(cause) = cause.code()
&& let hir::Node::Block(blk) = self.tcx.hir_node(cause.then_id)
&& let Some(then) = blk.expr
&& def.is_box()
&& let boxed_ty = args.type_at(0)
&& let ty::Dynamic(t, _, _) = boxed_ty.kind()
&& let Some(def_id) = t.principal_def_id()
&& let mut impl_def_ids = vec![]
&& let _ =
tcx.for_each_relevant_impl(def_id, values.expected, |did| {
impl_def_ids.push(did)
})
&& let [_] = &impl_def_ids[..] =>
{
// We have divergent if/else arms where the expected value is a type that
// implements the trait of the found boxed trait object.
diag.multipart_suggestion(
format!(
"`{}` implements `{}` so you can box it to coerce to the trait \
object `{}`",
values.expected,
tcx.item_name(def_id),
values.found,
),
vec![
(then.span.shrink_to_lo(), "Box::new(".to_string()),
(then.span.shrink_to_hi(), ")".to_string()),
],
MachineApplicable,
);
}
_ => {}
}
debug!(

32
tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed Normal file
View File

@ -0,0 +1,32 @@
// run-rustfix
trait Trait {}
struct Struct;
impl Trait for Struct {}
fn foo() -> Box<dyn Trait> {
Box::new(Struct)
}
fn bar() -> impl Trait {
Struct
}
fn main() {
let _ = if true {
Box::new(Struct)
} else {
foo() //~ ERROR E0308
};
let _ = if true {
foo()
} else {
Box::new(Struct) //~ ERROR E0308
};
let _ = if true {
Box::new(Struct) as Box<dyn Trait>
} else {
Box::new(bar()) //~ ERROR E0308
};
let _ = if true {
Box::new(bar()) as Box<dyn Trait>
} else {
Box::new(Struct) //~ ERROR E0308
};
}

32
tests/ui/typeck/suggest-box-on-divergent-if-else-arms.rs Normal file
View File

@ -0,0 +1,32 @@
// run-rustfix
trait Trait {}
struct Struct;
impl Trait for Struct {}
fn foo() -> Box<dyn Trait> {
Box::new(Struct)
}
fn bar() -> impl Trait {
Struct
}
fn main() {
let _ = if true {
Struct
} else {
foo() //~ ERROR E0308
};
let _ = if true {
foo()
} else {
Struct //~ ERROR E0308
};
let _ = if true {
Struct
} else {
bar() //~ ERROR E0308
};
let _ = if true {
bar()
} else {
Struct //~ ERROR E0308
};
}

94
tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr Normal file
View File

@ -0,0 +1,94 @@
error[E0308]: `if` and `else` have incompatible types
--> $DIR/suggest-box-on-divergent-if-else-arms.rs:15:9
|
LL | let _ = if true {
| _____________-
LL | | Struct
| | ------ expected because of this
LL | | } else {
LL | | foo()
| | ^^^^^ expected `Struct`, found `Box<dyn Trait>`
LL | | };
| |_____- `if` and `else` have incompatible types
|
= note: expected struct `Struct`
found struct `Box<dyn Trait>`
help: `Struct` implements `Trait` so you can box it to coerce to the trait object `Box<dyn Trait>`
|
LL | Box::new(Struct)
| +++++++++ +
error[E0308]: `if` and `else` have incompatible types
--> $DIR/suggest-box-on-divergent-if-else-arms.rs:20:9
|
LL | let _ = if true {
| _____________-
LL | | foo()
| | ----- expected because of this
LL | | } else {
LL | | Struct
| | ^^^^^^ expected `Box<dyn Trait>`, found `Struct`
LL | | };
| |_____- `if` and `else` have incompatible types
|
= note: expected struct `Box<dyn Trait>`
found struct `Struct`
= note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html
help: store this in the heap by calling `Box::new`
|
LL | Box::new(Struct)
| +++++++++ +
error[E0308]: `if` and `else` have incompatible types
--> $DIR/suggest-box-on-divergent-if-else-arms.rs:25:9
|
LL | fn bar() -> impl Trait {
| ---------- the found opaque type
...
LL | let _ = if true {
| _____________-
LL | | Struct
| | ------ expected because of this
LL | | } else {
LL | | bar()
| | ^^^^^ expected `Struct`, found opaque type
LL | | };
| |_____- `if` and `else` have incompatible types
|
= note: expected struct `Struct`
found opaque type `impl Trait`
help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box<dyn Trait>`
|
LL ~ Box::new(Struct) as Box<dyn Trait>
LL | } else {
LL ~ Box::new(bar())
|
error[E0308]: `if` and `else` have incompatible types
--> $DIR/suggest-box-on-divergent-if-else-arms.rs:30:9
|
LL | fn bar() -> impl Trait {
| ---------- the expected opaque type
...
LL | let _ = if true {
| _____________-
LL | | bar()
| | ----- expected because of this
LL | | } else {
LL | | Struct
| | ^^^^^^ expected opaque type, found `Struct`
LL | | };
| |_____- `if` and `else` have incompatible types
|
= note: expected opaque type `impl Trait`
found struct `Struct`
help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box<dyn Trait>`
|
LL ~ Box::new(bar()) as Box<dyn Trait>
LL | } else {
LL ~ Box::new(Struct)
|
error: aborting due to 4 previous errors
For more information about this error, try `rustc --explain E0308`.