From 6fd564112f1ec00f6f8a56e8a3577dd255639131 Mon Sep 17 00:00:00 2001 From: Esteban Küber Date: Mon, 13 Jan 2020 13:13:12 -0800 Subject: Specific error for unsized `dyn Trait` return type Suggest `impl Trait` when possible, and `Box` otherwise. --- src/test/ui/error-codes/E0746.rs | 17 ++ src/test/ui/error-codes/E0746.stderr | 62 +++++++ .../dyn-trait-return-should-be-impl-trait.rs | 36 ++++ .../dyn-trait-return-should-be-impl-trait.stderr | 186 +++++++++++++++++++++ 4 files changed, 301 insertions(+) create mode 100644 src/test/ui/error-codes/E0746.rs create mode 100644 src/test/ui/error-codes/E0746.stderr create mode 100644 src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.rs create mode 100644 src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.stderr (limited to 'src/test') diff --git a/src/test/ui/error-codes/E0746.rs b/src/test/ui/error-codes/E0746.rs new file mode 100644 index 00000000000..ad257b01e1b --- /dev/null +++ b/src/test/ui/error-codes/E0746.rs @@ -0,0 +1,17 @@ +struct Struct; +trait Trait {} +impl Trait for Struct {} +impl Trait for u32 {} + +fn foo() -> dyn Trait { Struct } +//~^ ERROR E0746 +//~| ERROR E0308 + +fn bar() -> dyn Trait { //~ ERROR E0746 + if true { + return 0; //~ ERROR E0308 + } + 42 //~ ERROR E0308 +} + +fn main() {} diff --git a/src/test/ui/error-codes/E0746.stderr b/src/test/ui/error-codes/E0746.stderr new file mode 100644 index 00000000000..baafcd27c29 --- /dev/null +++ b/src/test/ui/error-codes/E0746.stderr @@ -0,0 +1,62 @@ +error[E0308]: mismatched types + --> $DIR/E0746.rs:6:25 + | +LL | fn foo() -> dyn Trait { Struct } + | --------- ^^^^^^ expected trait `Trait`, found struct `Struct` + | | + | expected `(dyn Trait + 'static)` because of return type + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/E0746.rs:6:13 + | +LL | fn foo() -> dyn Trait { Struct } + | ^^^^^^^^^ doesn't have a size known at compile-time + | + = note: for information on `impl Trait`, see +help: you can use the `impl Trait` feature in the return type because all the return paths are of type `Struct`, which implements `dyn Trait` + | +LL | fn foo() -> impl Trait { Struct } + | ^^^^^^^^^^ + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/E0746.rs:10:13 + | +LL | fn bar() -> dyn Trait { + | ^^^^^^^^^ doesn't have a size known at compile-time + | + = note: for information on `impl Trait`, see +help: you can use the `impl Trait` feature in the return type because all the return paths are of type `{integer}`, which implements `dyn Trait` + | +LL | fn bar() -> impl Trait { + | ^^^^^^^^^^ + +error[E0308]: mismatched types + --> $DIR/E0746.rs:12:16 + | +LL | fn bar() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +LL | if true { +LL | return 0; + | ^ expected trait `Trait`, found integer + | + = note: expected trait object `(dyn Trait + 'static)` + found type `{integer}` + +error[E0308]: mismatched types + --> $DIR/E0746.rs:14:5 + | +LL | fn bar() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +... +LL | 42 + | ^^ expected trait `Trait`, found integer + | + = note: expected trait object `(dyn Trait + 'static)` + found type `{integer}` + +error: aborting due to 5 previous errors + +For more information about this error, try `rustc --explain E0308`. diff --git a/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.rs b/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.rs new file mode 100644 index 00000000000..80168ca8257 --- /dev/null +++ b/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.rs @@ -0,0 +1,36 @@ +#![allow(bare_trait_objects)] +struct Struct; +trait Trait {} +impl Trait for Struct {} +impl Trait for u32 {} + +fn fuz() -> (usize, Trait) { (42, Struct) } +//~^ ERROR E0277 +//~| ERROR E0308 +fn bar() -> (usize, dyn Trait) { (42, Struct) } +//~^ ERROR E0277 +//~| ERROR E0308 +fn bap() -> Trait { Struct } +//~^ ERROR E0746 +//~| ERROR E0308 +fn ban() -> dyn Trait { Struct } +//~^ ERROR E0746 +//~| ERROR E0308 +fn bak() -> dyn Trait { unimplemented!() } //~ ERROR E0277 +// Suggest using `Box` +fn bal() -> dyn Trait { //~ ERROR E0746 + if true { + return Struct; //~ ERROR E0308 + } + 42 //~ ERROR E0308 +} + +// Suggest using `impl Trait` +fn bat() -> dyn Trait { //~ ERROR E0746 + if true { + return 0; //~ ERROR E0308 + } + 42 //~ ERROR E0308 +} + +fn main() {} diff --git a/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.stderr b/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.stderr new file mode 100644 index 00000000000..ce4c141a0af --- /dev/null +++ b/src/test/ui/impl-trait/dyn-trait-return-should-be-impl-trait.stderr @@ -0,0 +1,186 @@ +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:7:35 + | +LL | fn fuz() -> (usize, Trait) { (42, Struct) } + | ^^^^^^ expected trait `Trait`, found struct `Struct` + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0277]: the size for values of type `(dyn Trait + 'static)` cannot be known at compilation time + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:7:13 + | +LL | fn fuz() -> (usize, Trait) { (42, Struct) } + | ^^^^^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: within `(usize, (dyn Trait + 'static))`, the trait `std::marker::Sized` is not implemented for `(dyn Trait + 'static)` + = note: to learn more, visit + = note: required because it appears within the type `(usize, (dyn Trait + 'static))` + = note: the return type of a function must have a statically known size + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:10:39 + | +LL | fn bar() -> (usize, dyn Trait) { (42, Struct) } + | ^^^^^^ expected trait `Trait`, found struct `Struct` + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0277]: the size for values of type `(dyn Trait + 'static)` cannot be known at compilation time + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:10:13 + | +LL | fn bar() -> (usize, dyn Trait) { (42, Struct) } + | ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: within `(usize, (dyn Trait + 'static))`, the trait `std::marker::Sized` is not implemented for `(dyn Trait + 'static)` + = note: to learn more, visit + = note: required because it appears within the type `(usize, (dyn Trait + 'static))` + = note: the return type of a function must have a statically known size + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:13:21 + | +LL | fn bap() -> Trait { Struct } + | ----- ^^^^^^ expected trait `Trait`, found struct `Struct` + | | + | expected `(dyn Trait + 'static)` because of return type + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:13:13 + | +LL | fn bap() -> Trait { Struct } + | ^^^^^ doesn't have a size known at compile-time + | + = note: for information on `impl Trait`, see +help: you can use the `impl Trait` feature in the return type because all the return paths are of type `Struct`, which implements `dyn Trait` + | +LL | fn bap() -> impl Trait { Struct } + | ^^^^^^^^^^ + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:16:25 + | +LL | fn ban() -> dyn Trait { Struct } + | --------- ^^^^^^ expected trait `Trait`, found struct `Struct` + | | + | expected `(dyn Trait + 'static)` because of return type + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:16:13 + | +LL | fn ban() -> dyn Trait { Struct } + | ^^^^^^^^^ doesn't have a size known at compile-time + | + = note: for information on `impl Trait`, see +help: you can use the `impl Trait` feature in the return type because all the return paths are of type `Struct`, which implements `dyn Trait` + | +LL | fn ban() -> impl Trait { Struct } + | ^^^^^^^^^^ + +error[E0277]: the size for values of type `(dyn Trait + 'static)` cannot be known at compilation time + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:19:13 + | +LL | fn bak() -> dyn Trait { unimplemented!() } + | ^^^^^^^^^ doesn't have a size known at compile-time + | + = help: the trait `std::marker::Sized` is not implemented for `(dyn Trait + 'static)` + = note: to learn more, visit + = note: the return type of a function must have a statically known size + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:23:16 + | +LL | fn bal() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +LL | if true { +LL | return Struct; + | ^^^^^^ expected trait `Trait`, found struct `Struct` + | + = note: expected trait object `(dyn Trait + 'static)` + found struct `Struct` + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:21:13 + | +LL | fn bal() -> dyn Trait { + | ^^^^^^^^^ doesn't have a size known at compile-time + | +help: if all the returned values were of the same type you could use `impl Trait` as the return type + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:25:5 + | +LL | return Struct; + | ^^^^^^ +LL | } +LL | 42 + | ^^ + = help: alternatively, you can always create a new `enum` with a variant for each returned type + = note: for information on `impl Trait`, see + = note: for information on trait objects, see +help: if the performance implications are acceptable, you can return a trait object + | +LL | fn bal() -> Box { +LL | if true { +LL | return Box::new(Struct); +LL | } +LL | Box::new(42) + | + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:25:5 + | +LL | fn bal() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +... +LL | 42 + | ^^ expected trait `Trait`, found integer + | + = note: expected trait object `(dyn Trait + 'static)` + found type `{integer}` + +error[E0746]: return type cannot have a bare trait because it must be `Sized` + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:29:13 + | +LL | fn bat() -> dyn Trait { + | ^^^^^^^^^ doesn't have a size known at compile-time + | + = note: for information on `impl Trait`, see +help: you can use the `impl Trait` feature in the return type because all the return paths are of type `{integer}`, which implements `dyn Trait` + | +LL | fn bat() -> impl Trait { + | ^^^^^^^^^^ + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:31:16 + | +LL | fn bat() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +LL | if true { +LL | return 0; + | ^ expected trait `Trait`, found integer + | + = note: expected trait object `(dyn Trait + 'static)` + found type `{integer}` + +error[E0308]: mismatched types + --> $DIR/dyn-trait-return-should-be-impl-trait.rs:33:5 + | +LL | fn bat() -> dyn Trait { + | --------- expected `(dyn Trait + 'static)` because of return type +... +LL | 42 + | ^^ expected trait `Trait`, found integer + | + = note: expected trait object `(dyn Trait + 'static)` + found type `{integer}` + +error: aborting due to 15 previous errors + +Some errors have detailed explanations: E0277, E0308. +For more information about an error, try `rustc --explain E0277`. -- cgit 1.4.1-3-g733a5