Prevent @babel/traverse path cache side-effects in generateFunctionMap
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…nMap` Summary: ## Motivation For performance reasons, we'd like to have the option to re-use an AST (without cloning) after deriving source map information from it. However, due to babel/babel#6437, traversing the AST within `generateFunctionMap` causes the `babel/traverse` path cache to be populated with entries Babel transform plugins can't use - in particular because `hub` is assumed to be set. ## Change This diffs saves and clears the traverse cache before traversal, and then restores it afterwards. This isn't pretty but it's the cleanest approach I could find - we include tests to verify that this is (and continues to be) necessary. ## Other approaches I tried some other things before resorting to manipulating `babel/traverse` internals: - Actually providing a `hub` so that it's set on the cache means adding a dependency on `babel/core`, and requires a similar level of hackery / assumptions of Babel internals. - Clearing the bad cache with `traverse.clearNode(ast)` or `traverse.cache.clearPath()` doesn't work because other tools (eg, Jest) rely on `properties` held in the path cache. Changelog: [Internal] Differential Revision: D42068914 fbshipit-source-id: f473f67f17ffe92c9fc378ef54f3dc40bcf25f7a
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Summary:
Motivation
For performance reasons, we'd like to have the option to re-use an AST (without cloning) after deriving source map information from it. However, due to babel/babel#6437, traversing the AST within
generateFunctionMapcauses thebabel/traversepath cache to be populated with entries Babel transform plugins can't use - in particular becausehubis assumed to be set.Change
This diffs saves and clears the traverse cache before traversal, and then restores it afterwards. This isn't pretty but it's the cleanest approach I could find - we include tests to verify that this is (and continues to be) necessary.
Other approaches
I tried some other things before resorting to manipulating
babel/traverseinternals:hubso that it's set on the cache means adding a dependency onbabel/core, and requires a similar level of hackery / assumptions of Babel internals.traverse.clearNode(ast)ortraverse.cache.clearPath()doesn't work because other tools (eg, Jest) rely onpropertiesheld in the path cache.Changelog: [Internal]
Differential Revision: D42068914