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More accurate suggestion for -> Box<dyn Trait> or -> impl Trait

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When encountering `-> Trait`, suggest `-> Box<dyn Trait>` (instead of `-> Box<Trait>`.

If there's a single returned type within the `fn`, suggest `-> impl Trait`.
This commit is contained in:
Esteban Küber 2024-07-19 19:39:37 +00:00
parent 3811f40d27
commit 3ff758877f
9 changed files with 72 additions and 65 deletions
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50
compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
View File

@ -1793,25 +1793,42 @@ fn suggest_impl_trait(
err.children.clear();
let span = obligation.cause.span;
if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span)
&& snip.starts_with("dyn ")
{
err.span_suggestion(
span.with_hi(span.lo() + BytePos(4)),
"return an `impl Trait` instead of a `dyn Trait`, \
if all returned values are the same type",
"impl ",
Applicability::MaybeIncorrect,
);
}
let body = self.tcx.hir().body_owned_by(obligation.cause.body_id);
let mut visitor = ReturnsVisitor::default();
visitor.visit_body(&body);
let mut sugg =
vec![(span.shrink_to_lo(), "Box<".to_string()), (span.shrink_to_hi(), ">".to_string())];
let (pre, impl_span) = if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span)
&& snip.starts_with("dyn ")
{
("", span.with_hi(span.lo() + BytePos(4)))
} else {
("dyn ", span.shrink_to_lo())
};
let alternatively = if visitor
.returns
.iter()
.map(|expr| self.typeck_results.as_ref().unwrap().expr_ty_adjusted_opt(expr))
.collect::<FxHashSet<_>>()
.len()
<= 1
{
err.span_suggestion_verbose(
impl_span,
"consider returning an `impl Trait` instead of a `dyn Trait`",
"impl ",
Applicability::MaybeIncorrect,
);
"alternatively, "
} else {
err.help("if there were a single returned type, you could use `impl Trait` instead");
""
};
let mut sugg = vec![
(span.shrink_to_lo(), format!("Box<{pre}")),
(span.shrink_to_hi(), ">".to_string()),
];
sugg.extend(visitor.returns.into_iter().flat_map(|expr| {
let span =
expr.span.find_ancestor_in_same_ctxt(obligation.cause.span).unwrap_or(expr.span);
@ -1837,7 +1854,10 @@ fn suggest_impl_trait(
}));
err.multipart_suggestion(
"box the return type, and wrap all of the returned values in `Box::new`",
format!(
"{alternatively}box the return type, and wrap all of the returned values in \
`Box::new`",
),
sugg,
Applicability::MaybeIncorrect,
);

9
tests/ui/error-codes/E0746.stderr
View File

@ -4,11 +4,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn foo() -> dyn Trait { Struct }
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn foo() -> impl Trait { Struct }
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn foo() -> Box<dyn Trait> { Box::new(Struct) }
| ++++ + +++++++++ +
@ -19,10 +19,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bar() -> dyn Trait {
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn bar() -> impl Trait {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn bar() -> Box<dyn Trait> {

38
tests/ui/impl-trait/dyn-trait-return-should-be-impl-trait.stderr
View File

@ -48,10 +48,14 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bap() -> Trait { Struct }
| ^^^^^ doesn't have a size known at compile-time
|
help: box the return type, and wrap all of the returned values in `Box::new`
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn bap() -> Box<Trait> { Box::new(Struct) }
| ++++ + +++++++++ +
LL | fn bap() -> impl Trait { Struct }
| ++++
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn bap() -> Box<dyn Trait> { Box::new(Struct) }
| +++++++ + +++++++++ +
error[E0746]: return type cannot have an unboxed trait object
--> $DIR/dyn-trait-return-should-be-impl-trait.rs:15:13
@ -59,11 +63,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn ban() -> dyn Trait { Struct }
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn ban() -> impl Trait { Struct }
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn ban() -> Box<dyn Trait> { Box::new(Struct) }
| ++++ + +++++++++ +
@ -74,11 +78,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bak() -> dyn Trait { unimplemented!() }
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn bak() -> impl Trait { unimplemented!() }
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn bak() -> Box<dyn Trait> { Box::new(unimplemented!()) }
| ++++ + +++++++++ +
@ -89,10 +93,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bal() -> dyn Trait {
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn bal() -> impl Trait {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn bal() -> Box<dyn Trait> {
@ -108,10 +109,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bax() -> dyn Trait {
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn bax() -> impl Trait {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn bax() -> Box<dyn Trait> {
@ -263,10 +261,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bat() -> dyn Trait {
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn bat() -> impl Trait {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn bat() -> Box<dyn Trait> {
@ -282,10 +277,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn bay() -> dyn Trait {
| ^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn bay() -> impl Trait {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn bay() -> Box<dyn Trait> {

5
tests/ui/impl-trait/object-unsafe-trait-in-return-position-dyn-trait.stderr
View File

@ -54,10 +54,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn car() -> dyn NotObjectSafe {
| ^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn car() -> impl NotObjectSafe {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn car() -> Box<dyn NotObjectSafe> {

13
tests/ui/impl-trait/point-to-type-err-cause-on-impl-trait-return.stderr
View File

@ -171,11 +171,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn hat() -> dyn std::fmt::Display {
| ^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn hat() -> impl std::fmt::Display {
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn hat() -> Box<dyn std::fmt::Display> {
LL | match 13 {
@ -192,11 +192,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn pug() -> dyn std::fmt::Display {
| ^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn pug() -> impl std::fmt::Display {
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn pug() -> Box<dyn std::fmt::Display> {
LL | match 13 {
@ -211,10 +211,7 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn man() -> dyn std::fmt::Display {
| ^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
|
LL | fn man() -> impl std::fmt::Display {
| ~~~~
= help: if there were a single returned type, you could use `impl Trait` instead
help: box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn man() -> Box<dyn std::fmt::Display> {

4
tests/ui/issues/issue-18107.stderr
View File

@ -4,11 +4,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | dyn AbstractRenderer
| ^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | impl AbstractRenderer
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ Box<dyn AbstractRenderer>
LL |

4
tests/ui/unsized/box-instead-of-dyn-fn.stderr
View File

@ -4,11 +4,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> dyn Fn() + 'a {
| ^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> impl Fn() + 'a {
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL ~ fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> Box<dyn Fn() + 'a> {
LL |

10
tests/ui/unsized/issue-91801.stderr
View File

@ -4,10 +4,14 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn or<'a>(first: &'static Validator<'a>, second: &'static Validator<'a>) -> Validator<'a> {
| ^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: box the return type, and wrap all of the returned values in `Box::new`
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn or<'a>(first: &'static Validator<'a>, second: &'static Validator<'a>) -> Box<Validator<'a>> {
| ++++ +
LL | fn or<'a>(first: &'static Validator<'a>, second: &'static Validator<'a>) -> impl Validator<'a> {
| ++++
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn or<'a>(first: &'static Validator<'a>, second: &'static Validator<'a>) -> Box<dyn Validator<'a>> {
| +++++++ +
error: aborting due to 1 previous error

4
tests/ui/unsized/issue-91803.stderr
View File

@ -4,11 +4,11 @@ error[E0746]: return type cannot have an unboxed trait object
LL | fn or<'a>(first: &'static dyn Foo<'a>) -> dyn Foo<'a> {
| ^^^^^^^^^^^ doesn't have a size known at compile-time
|
help: return an `impl Trait` instead of a `dyn Trait`, if all returned values are the same type
help: consider returning an `impl Trait` instead of a `dyn Trait`
|
LL | fn or<'a>(first: &'static dyn Foo<'a>) -> impl Foo<'a> {
| ~~~~
help: box the return type, and wrap all of the returned values in `Box::new`
help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
|
LL | fn or<'a>(first: &'static dyn Foo<'a>) -> Box<dyn Foo<'a>> {
| ++++ +