6fcd589025
Move lev_distance to rustc_ast, make non-generic rustc_ast currently has a few dependencies on rustc_lexer. Ideally, an AST would not have any dependency its lexer, for minimizing design-time dependencies. Breaking this dependency would also have practical benefits, since modifying rustc_lexer would not trigger a rebuild of rustc_ast. This commit does not remove the rustc_ast --> rustc_lexer dependency, but it does remove one of the sources of this dependency, which is the code that handles fuzzy matching between symbol names for making suggestions in diagnostics. Since that code depends only on Symbol, it is easy to move it to rustc_span. It might even be best to move it to a separate crate, since other tools such as Cargo use the same algorithm, and have simply contain a duplicate of the code. This changes the signature of find_best_match_for_name so that it is no longer generic over its input. I checked the optimized binaries, and this function was duplicated for nearly every call site, because most call sites used short-lived iterator chains, generic over Map and such. But there's no good reason for a function like this to be generic, since all it does is immediately convert the generic input (the Iterator impl) to a concrete Vec<Symbol>. This has all of the costs of generics (duplicated method bodies) with no benefit. Changing find_best_match_for_name to be non-generic removed about 10KB of code from the optimized binary. I know it's a drop in the bucket, but we have to start reducing binary size, and beginning to tame over-use of generics is part of that. |
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| Cargo.toml | ||
| README.md | ||
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: