Auto merge of #68522 - estebank:impl-trait-sugg-2, r=oli-obk
Further improve `impl Trait`/`dyn Trait` suggestions After reading [_Returning Trait Objects_ by Bryce Fisher-Fleig](https://bryce.fisher-fleig.org/blog/returning-trait-objects/), [I noticed that](https://www.reddit.com/r/rust/comments/esueur/returning_trait_objects/ffczl4k/) #68195 had a few bugs due to not ignoring `ty::Error`. - Account for `ty::Error`. - Account for `if`/`else` and `match` blocks when pointing at return types and referencing their types. - Increase the multiline suggestion output from 6 lines to 20.
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bors
commit
3d8778d767
5 changed files with 262 additions and 23 deletions
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@ -22,6 +22,39 @@ fn bal() -> dyn Trait { //~ ERROR E0746
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}
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42
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}
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fn bax() -> dyn Trait { //~ ERROR E0746
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if true {
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Struct
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} else {
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42
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}
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}
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fn bam() -> Box<dyn Trait> {
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if true {
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return Struct; //~ ERROR mismatched types
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}
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42 //~ ERROR mismatched types
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}
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fn baq() -> Box<dyn Trait> {
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if true {
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return 0; //~ ERROR mismatched types
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}
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42 //~ ERROR mismatched types
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}
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fn baz() -> Box<dyn Trait> {
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if true {
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Struct //~ ERROR mismatched types
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} else {
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42 //~ ERROR mismatched types
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}
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}
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fn baw() -> Box<dyn Trait> {
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if true {
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0 //~ ERROR mismatched types
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} else {
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42 //~ ERROR mismatched types
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}
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}
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// Suggest using `impl Trait`
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fn bat() -> dyn Trait { //~ ERROR E0746
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@ -30,5 +63,12 @@ fn bat() -> dyn Trait { //~ ERROR E0746
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}
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42
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}
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fn bay() -> dyn Trait { //~ ERROR E0746
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if true {
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0
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} else {
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42
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}
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}
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fn main() {}
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@ -96,7 +96,154 @@ LL | Box::new(42)
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error[E0746]: return type cannot have an unboxed trait object
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:27:13
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:25:13
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LL | fn bax() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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= note: for information on trait objects, see <https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types>
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= note: if all the returned values were of the same type you could use `impl Trait` as the return type
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= note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
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= note: you can create a new `enum` with a variant for each returned type
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help: return a boxed trait object instead
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LL | fn bax() -> Box<dyn Trait> {
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LL | if true {
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LL | Box::new(Struct)
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LL | } else {
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LL | Box::new(42)
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:34:16
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LL | fn bam() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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LL | if true {
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LL | return Struct;
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| ^^^^^^
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| |
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| expected struct `std::boxed::Box`, found struct `Struct`
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| help: store this in the heap by calling `Box::new`: `Box::new(Struct)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found struct `Struct`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:36:5
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LL | fn bam() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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...
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LL | 42
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| ^^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(42)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:40:16
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LL | fn baq() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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LL | if true {
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LL | return 0;
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| ^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(0)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:42:5
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LL | fn baq() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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...
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LL | 42
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| ^^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(42)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:46:9
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LL | fn baz() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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LL | if true {
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LL | Struct
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| ^^^^^^
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| |
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| expected struct `std::boxed::Box`, found struct `Struct`
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| help: store this in the heap by calling `Box::new`: `Box::new(Struct)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found struct `Struct`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:48:9
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LL | fn baz() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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...
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LL | 42
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| ^^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(42)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:53:9
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LL | fn baw() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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LL | if true {
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LL | 0
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| ^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(0)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:55:9
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LL | fn baw() -> Box<dyn Trait> {
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| -------------- expected `std::boxed::Box<(dyn Trait + 'static)>` because of return type
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...
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LL | 42
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| ^^
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| |
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| expected struct `std::boxed::Box`, found integer
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| help: store this in the heap by calling `Box::new`: `Box::new(42)`
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= note: expected struct `std::boxed::Box<(dyn Trait + 'static)>`
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found type `{integer}`
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= 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
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error[E0746]: return type cannot have an unboxed trait object
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:60:13
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LL | fn bat() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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@ -107,7 +254,19 @@ help: return `impl Trait` instead, as all return paths are of type `{integer}`,
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LL | fn bat() -> impl Trait {
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| ^^^^^^^^^^
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error: aborting due to 9 previous errors
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error[E0746]: return type cannot have an unboxed trait object
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:66:13
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LL | fn bay() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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= note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
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help: return `impl Trait` instead, as all return paths are of type `{integer}`, which implements `Trait`
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LL | fn bay() -> impl Trait {
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| ^^^^^^^^^^
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error: aborting due to 19 previous errors
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Some errors have detailed explanations: E0277, E0308, E0746.
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For more information about an error, try `rustc --explain E0277`.
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@ -5,7 +5,7 @@ LL | fn should_ret_unit() -> impl T {
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| ^^^^^^ the trait `T` is not implemented for `()`
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LL |
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LL | panic!()
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| -------- this returned value is of type `()`
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| -------- this returned value is of type `!`
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= note: the return type of a function must have a statically known size
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= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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