Jun Wu 3ffa0f28e2 gitignore: avoid quadratic behavior ... Summary: The correct gitignore matcher needs O(N^2) time to check a path which is N directory deep. For example, to check "a/b/c/d", it needs to check: - Whether .gitignore matches a/b/c/d - Whether a/.gitignore matches b/c/d - Whether a/b/.gitignore matches c/d - Whether a/b/c/.gitignore matches d - Whether .gitignore matches a/b/c - Whether a/.gitignore matches b/c - Whether a/b/.gitignore matches c - Whether .gitignore matches a/b - Whether a/.gitignore matches b - Whether .gitignore matches a It might not look that bad because N=4 for the above example. But when N is larger (ex. node_modules/../node_modules/../node_modules/..), things get much worse. This patch adds "caching" about whether a directory is ignored or not. For example, if "a/b/" is ignored, the new code would skip checking subdirectories (ex. "a/b/c/"). The time complexity is now roughly O(N) gitignore tests instead of O(N^2), since we only did a gitignore check for a parent directory of a path being tested once, and then cache the parent directory result in a boolean value. To be clear, for the first time checking a path which is not ignored, it still needs O(N^2) for initializing the trees. But once it's initialized, the next time checking a file in a same directory, will be O(N). `LruCache` is replaced by `HashMap` since it does not support `.get` and the code needs that to work. The perf issue was previously documented as a "PERF" comment. This diff removes it. Reviewed By: DurhamG Differential Revision: D7496058 fbshipit-source-id: f10895b8f0d7dcdde6faf9daeec5cd78a1f15a2b		2018-04-13 21:51:48 -07:00
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src	gitignore: avoid quadratic behavior	2018-04-13 21:51:48 -07:00
Cargo.toml	gitignore: avoid quadratic behavior	2018-04-13 21:51:48 -07:00