diff --git a/src/doc/unstable-book/src/language-features/on-unimplemented.md b/src/doc/unstable-book/src/language-features/on-unimplemented.md index f787f629756..a770ab65c26 100644 --- a/src/doc/unstable-book/src/language-features/on-unimplemented.md +++ b/src/doc/unstable-book/src/language-features/on-unimplemented.md @@ -138,3 +138,16 @@ error[E0277]: `&str` is not an iterator = help: the trait `std::iter::Iterator` is not implemented for `&str` = note: required by `std::iter::IntoIterator::into_iter` ``` + +If you need to filter on multiple attributes, you can use `all`, `any` or +`not` in the following way: + +```rust,compile_fail +#[rustc_on_unimplemented( + on( + all(_Self="&str", T="std::string::String"), + note="you can coerce a `{T}` into a `{Self}` by writing `&*variable`" + ) +)] +pub trait From: Sized { /* ... */ } +``` diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs index cee4fc6f49a..a6c65e890a5 100644 --- a/src/libcore/convert.rs +++ b/src/libcore/convert.rs @@ -363,6 +363,12 @@ pub trait Into: Sized { /// [`from`]: trait.From.html#tymethod.from /// [book]: ../../book/ch09-00-error-handling.html #[stable(feature = "rust1", since = "1.0.0")] +#[rustc_on_unimplemented( + on( + all(_Self="&str", T="std::string::String"), + note="to coerce a `{T}` into a `{Self}`, use `&*` as a prefix", + ) +)] pub trait From: Sized { /// Performs the conversion. #[stable(feature = "rust1", since = "1.0.0")] diff --git a/src/test/ui/suggestions/into-str.rs b/src/test/ui/suggestions/into-str.rs new file mode 100644 index 00000000000..9793ee801d1 --- /dev/null +++ b/src/test/ui/suggestions/into-str.rs @@ -0,0 +1,6 @@ +fn foo<'a, T>(_t: T) where T: Into<&'a str> {} + +fn main() { + foo(String::new()); + //~^ ERROR the trait bound `&str: std::convert::From` is not satisfied +} diff --git a/src/test/ui/suggestions/into-str.stderr b/src/test/ui/suggestions/into-str.stderr new file mode 100644 index 00000000000..3e28700ce95 --- /dev/null +++ b/src/test/ui/suggestions/into-str.stderr @@ -0,0 +1,17 @@ +error[E0277]: the trait bound `&str: std::convert::From` is not satisfied + --> $DIR/into-str.rs:4:5 + | +LL | foo(String::new()); + | ^^^ the trait `std::convert::From` is not implemented for `&str` + | + = note: to coerce a `std::string::String` into a `&str`, use `&*` as a prefix + = note: required because of the requirements on the impl of `std::convert::Into<&str>` for `std::string::String` +note: required by `foo` + --> $DIR/into-str.rs:1:1 + | +LL | fn foo<'a, T>(_t: T) where T: Into<&'a str> {} + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0277`.