rust/compiler/rustc_ast
Aaron Hill a93c4f05de
Implement token-based handling of attributes during expansion
This PR modifies the macro expansion infrastructure to handle attributes
in a fully token-based manner. As a result:

* Derives macros no longer lose spans when their input is modified
  by eager cfg-expansion. This is accomplished by performing eager
  cfg-expansion on the token stream that we pass to the derive
  proc-macro
* Inner attributes now preserve spans in all cases, including when we
  have multiple inner attributes in a row.

This is accomplished through the following changes:

* New structs `AttrAnnotatedTokenStream` and `AttrAnnotatedTokenTree` are introduced.
  These are very similar to a normal `TokenTree`, but they also track
  the position of attributes and attribute targets within the stream.
  They are built when we collect tokens during parsing.
  An `AttrAnnotatedTokenStream` is converted to a regular `TokenStream` when
  we invoke a macro.
* Token capturing and `LazyTokenStream` are modified to work with
  `AttrAnnotatedTokenStream`. A new `ReplaceRange` type is introduced, which
  is created during the parsing of a nested AST node to make the 'outer'
  AST node aware of the attributes and attribute target stored deeper in the token stream.
* When we need to perform eager cfg-expansion (either due to `#[derive]` or `#[cfg_eval]`),
we tokenize and reparse our target, capturing additional information about the locations of
`#[cfg]` and `#[cfg_attr]` attributes at any depth within the target.
This is a performance optimization, allowing us to perform less work
in the typical case where captured tokens never have eager cfg-expansion run.
2021-04-11 01:31:36 -04:00
..
src Implement token-based handling of attributes during expansion 2021-04-11 01:31:36 -04:00
Cargo.toml bumped smallvec deps 2021-02-14 18:03:11 +03:00
README.md mv compiler to compiler/ 2020-08-30 18:45:07 +03:00

The rustc_ast crate contains those things concerned purely with syntax that is, the AST ("abstract syntax tree"), parser, pretty-printer, lexer, macro expander, and utilities for traversing ASTs.

For more information about how these things work in rustc, see the rustc dev guide: