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Rollup merge of rust-lang#120261 - estebank:issue-102629, r=wesleywiser
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)
|
```
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32
tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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 | ||
| }; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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 changes: 94 additions & 0 deletions
94
tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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`. |