[7.2.0] Automatically map paths in Args#map_each
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When path mapping is enabled, `File` objects accessed in a user-supplied callback passed to `Args#map_each` automatically have their paths mapped. Automatic rewriting is preferable to e.g. passing a rewriter object into the callback: All paths emitted into command lines must be rewritten with path mapping as inputs and outputs are staged at the mapped locations, so the user would need to manually map all paths - there is no choice. As an added benefit, the automatic rewriting ensures that existing rules relying on `map_each` do not need to be modified to use path mapping. This is a reland of 955b31e, which got rolled back due to a 7% CPU time increase on a benchmark caused by frequent comparisons of equal but not reference equal `StarlarkSemantics` used as keys in the `StarlarkClassDescriptor` cache in `CallUtils`. Instead of overriding `equals` and `hashCode` for `PathMapper`, this change subclasses `StarlarkSemantics` to provide a different, reference equal instance as the cache key. This is safe since the value associated with the `path_mapper` key does not affect the availability of any Starlark field or method, just the behavior of their implementations. Work towards bazelbuild#6526 Closes bazelbuild#21952. PiperOrigin-RevId: 629546010 Change-Id: Ib21fa2371a28a02f0c868523b410c5a40c2c6c82
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When path mapping is enabled,
Fileobjects accessed in a user-supplied callback passed toArgs#map_eachautomatically have their paths mapped.Automatic rewriting is preferable to e.g. passing a rewriter object into the callback: All paths emitted into command lines must be rewritten with path mapping as inputs and outputs are staged at the mapped locations, so the user would need to manually map all paths - there is no choice. As an added benefit, the automatic rewriting ensures that existing rules relying on
map_eachdo not need to be modified to use path mapping.This is a reland of 955b31e, which got rolled back due to a 7% CPU time increase on a benchmark caused by frequent comparisons of equal but not reference equal
StarlarkSemanticsused as keys in theStarlarkClassDescriptorcache inCallUtils. Instead of overridingequalsandhashCodeforPathMapper, this change subclassesStarlarkSemanticsto provide a different, reference equal instance as the cache key. This is safe since the value associated with thepath_mapperkey does not affect the availability of any Starlark field or method, just the behavior of their implementations.Work towards #6526
Closes #21952.
PiperOrigin-RevId: 629546010
Change-Id: Ib21fa2371a28a02f0c868523b410c5a40c2c6c82
Commit d474fcc