Matthias Krüger 32d85c0b5a Rollup merge of #92164 - WaffleLapkin:rustc_must_implement_one_of_attr, r=Aaron1011 ... Implement `#[rustc_must_implement_one_of]` attribute This PR adds a new attribute — `#[rustc_must_implement_one_of]` that allows changing the "minimal complete definition" of a trait. It's similar to GHC's minimal `{-# MINIMAL #-}` pragma, though `#[rustc_must_implement_one_of]` is weaker atm. Such attribute was long wanted. It can be, for example, used in `Read` trait to make transitions to recently added `read_buf` easier: ```rust #[rustc_must_implement_one_of(read, read_buf)] pub trait Read { fn read(&mut self, buf: &mut [u8]) -> Result<usize> { let mut buf = ReadBuf::new(buf); self.read_buf(&mut buf)?; Ok(buf.filled_len()) } fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> { default_read_buf(|b| self.read(b), buf) } } impl Read for Ty0 {} //^ This will fail to compile even though all `Read` methods have default implementations // Both of these will compile just fine impl Read for Ty1 { fn read(&mut self, buf: &mut [u8]) -> Result<usize> { /* ... */ } } impl Read for Ty2 { fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> { /* ... */ } } ``` For now, this is implemented as an internal attribute to start experimenting on the design of this feature. In the future we may want to extend it: - Allow arbitrary requirements like `a | (b & c)` - Allow multiple requirements like - ```rust #[rustc_must_implement_one_of(a, b)] #[rustc_must_implement_one_of(c, d)] ``` - Make it appear in rustdoc documentation - Change the syntax? - Etc Eventually, we should make an RFC and make this (or rather similar) attribute public. --- I'm fairly new to compiler development and not at all sure if the implementation makes sense, but at least it passes tests :)		2022-01-17 20:07:02 +01:00
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src	Rollup merge of #92164 - WaffleLapkin:rustc_must_implement_one_of_attr, r=Aaron1011	2022-01-17 20:07:02 +01:00
Cargo.toml	Migrate to 2021	2021-09-20 22:21:42 -04:00