2a18d124aa
Lazify `SourceFile::lines`. `SourceFile::lines` is a big part of metadata. It's stored in a compressed form (a difference list) to save disk space. Decoding it is a big fraction of compile time for very small crates/programs. This commit introduces a new type `SourceFileLines` which has a `Lines` form and a `Diffs` form. The latter is used when the metadata is first read, and it is only decoded into the `Lines` form when line data is actually needed. This avoids the decoding cost for many files, especially in `std`. It's a performance win of up to 15% for tiny crates/programs where metadata decoding is a high part of compilation costs. A `RefCell` is needed because the methods that access lines data (which can trigger decoding) take `&self` rather than `&mut self`. To allow for this, `SourceFile::lines` now takes a `FnMut` that operates on the lines slice rather than returning the lines slice. r? `@Mark-Simulacrum` |
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| Cargo.toml | ||