78948ac259
expand: Leave traces when expanding `cfg_attr` attributes Currently `cfg_trace` just disappears during expansion, but after this PR `#[cfg_attr(some tokens)]` will leave a `#[cfg_attr_trace(some tokens)]` attribute instead of itself in AST after expansion (the new attribute is built-in and inert, its inner tokens are the same as in the original attribute). This trace attribute can then be used by lints or other diagnostics, #133823 has some examples. Tokens in these trace attributes are set to an empty token stream, so the traces are non-existent for proc macros and cannot affect any user-observable behavior. This is also a weakness, because if a proc macro processes some code with the trace attributes, they will be lost, so the traces are best effort rather than precise. The next step is to do the same thing with `cfg` attributes (`#[cfg(TRUE)]` currently remains in both AST and tokens after expanding, it should be replaced with a trace instead). The idea belongs to `@estebank.` |
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This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.
Why Rust?
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Performance: Fast and memory-efficient, suitable for critical services, embedded devices, and easily integrated with other languages.
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Reliability: Our rich type system and ownership model ensure memory and thread safety, reducing bugs at compile-time.
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Productivity: Comprehensive documentation, a compiler committed to providing great diagnostics, and advanced tooling including package manager and build tool (Cargo), auto-formatter (rustfmt), linter (Clippy) and editor support (rust-analyzer).
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Read "Installation" from The Book.
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See CONTRIBUTING.md.
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See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.
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