Make SymlinkForest simpler and more efficient (Second try)

Bazel rebuilds the symlink tree under the execution root before every build to ensure source files from main repo and external repos are available and up to date. But the SymlinkForest has accumulated many legacy behaviors that is currently not necessary and inefficient. This change tries to simplify the logic and make it much more faster.

The main improvement is that instead of linking every file and dir under the top-level directory for every external repo, we only create a link to the top-level directory of the external repo. This will reduce a large amount of symlink create operations, which speeds up the preparing phase a lot on Windows.

Fixes: https://github.com/bazelbuild/bazel/issues/8545

RELNOTES: paths under the execution root starting with "." or "_" will be re-linked across builds
PiperOrigin-RevId: 253985611
3 files changed
tree: 36063d70779b4551566a6b8f2a29571a395b7353
  1. .bazelci/
  2. examples/
  3. scripts/
  4. site/
  5. src/
  6. third_party/
  7. tools/
  8. .bazelrc
  9. .gitattributes
  10. .gitignore
  11. AUTHORS
  12. BUILD
  13. CHANGELOG.md
  14. CODEOWNERS
  15. combine_distfiles.py
  16. combine_distfiles_to_tar.sh
  17. compile.sh
  18. CONTRIBUTING.md
  19. CONTRIBUTORS
  20. distdir.bzl
  21. ISSUE_TEMPLATE.md
  22. LICENSE
  23. README.md
  24. WORKSPACE
README.md

Bazel

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