Make source type generic #147
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**THIS IS A BREAKING CHANGE** When porting Arret from `codespan` 0.3 (see etaoins/arret#160) one of the missing features was being able use non-`String` types for storing source. Arret has two potential uses for this: 1. When loading native libraries exposing Arret functions (known as RFI libraries) their Arret type is specified as a per-function `&'static str`. An example can be seen here: https://github.com/etaoins/arret/blob/dfc41bed1c992cc57023359743f68c639d667f25/stdlib/rust/list.rs#L8 With `codespan` 0.3 we used `Cow<'static str>` to avoid allocating a new `String` for every RFI function by pointing directly inside the loaded library's binary. 2. Arret is multithreaded but needs to maintain a global `Files` instance to allocate `FileId`s. It uses a read-write lock for thread safety and is sensitive to contention on that lock in some circumstances. Because we need a `FileId` in our AST we can't parse the source to AST until we've added it to `Files`. However, because `Files` takes ownership of the source we need to hold a read lock on `Files` to use `files.source()`. The effectively serialises loading source files across all threads. Previously we used `Arc<FileMap>` to drop the lock on `CodeMap` and then parse the `FileMap` locklessly. The API doesn't allow this anymore but we could use `Source = Arc<str>` to similar effect. Unfortunately the above two uses are mutually exclusive using standard library types. However, either one is an improvement over `String` and a crate type like `supercow` could potentially satisfy both uses. This is a breaking change due to adding a new generic parameter to `Files`. I initially attempted to use a default of `String` but this doesn't work for `Files::new` due to rust-lang/rust#27336. See rust-lang/wg-allocators#1 for an analogous case to this.
This ports `codespan-reporting` and `codespan-lsp` to use `Files`'s new `Source` generic parameter.
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This looks good! I think I broke it with one of the merges - but it might be nice to get this into 0.7 - see #142. |
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No worries, I’ll rebase this when I get home 👍 |
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@brendanzab Updated! |
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THIS IS A BREAKING CHANGE
When porting Arret from
codespan0.3 (see etaoins/arret#160) one of the missing features was being able use non-Stringtypes for storing source.Arret has two potential uses for this:
When loading native libraries exposing Arret functions (known as RFI libraries) their Arret type is specified as a per-function
&'static str. An example can be seen here:https://github.com/etaoins/arret/blob/dfc41bed1c992cc57023359743f68c639d667f25/stdlib/rust/list.rs#L8
With
codespan0.3 we usedCow<'static str>to avoid allocating a newStringfor every RFI function by pointing directly inside the loaded library's binary.Arret is multithreaded but needs to maintain a global
Filesinstance to allocateFileIds. It uses a read-write lock for thread safety and is sensitive to contention on that lock in some circumstances.Because we need a
FileIdin our AST we can't parse the source to AST until we've added it toFiles. However, becauseFilestakes ownership of the source we need to hold a read lock onFilesto usefiles.source(). The effectively serialises loading source files across all threads.Previously we used
Arc<FileMap>to drop the lock onCodeMapand then parse theFileMaplocklessly. The API doesn't allow this anymore but we could useSource = Arc<str>to similar effect.Unfortunately the above two uses are mutually exclusive using standard library types. However, either one is an improvement over
Stringand a crate type likesupercowcould potentially satisfy both uses.This is a breaking change due to adding a new generic parameter to
Files. I initially attempted to use a default ofStringbut this doesn't work forFiles::newdue to rust-lang/rust#27336. See rust-lang/wg-allocators#1 for an analogous case to this.