Make dependency files deterministic #11818
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The dependency file generated by Clang can sometimes contain absolute paths to system headers, system modules and files generated by Bazel during the build. These paths can defer between machines and between Bazel instances, for example: ``` bazel-out/apl-darwin_x86_64-fastbuild/bin/_objs/B/arc/B.o: B.m \ /private/var/tmp/_bazel_user/b4422045cf7215be2d3fa4e439c7376a/sandbox/darwin-sandbox/214/execroot/__main__/bazel-out/apl-darwin_x86_64-fastbuild/bin/A.modulemap \ /Applications/Xcode-11.6.0.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Foundation.framework/Modules/module.modulemap ``` This patch adds a post-process to wrapped_clang to normalize those paths by: * converting absolute paths to relative paths for paths to files under the execution root * standardizing the paths to system headers, system modules to always use the standard location of Xcode (`/Applications/Xcode.app`). The user doesn't need to have Xcode installed to this location as Bazel are already mapping them to the correct location locally. This makes the produced `.d` files deterministic and can reliably be shared with the remote cache. Fixes bazelbuild#11817.
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So it doesn't matter when downloading these files if these paths are valid? Maybe we should remove the Xcode prefix entirely? |
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Removing the Xcode prefix breaks the builds. It seems Bazel needs it for remapping. |
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@trybka Hi. Could you take a look or request a review for this? |
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Hi @trybka, @googlewalt and/or @bbarenblat, could you take a brief look and share if this change makes sense? |
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See comment here: #11817 (comment) Notably, if these are harmless, it seems wasteful to clean them up in this manner. |
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The dependency file generated by Clang can sometimes contain absolute
paths to system headers, system modules and files generated by Bazel
during the build. These paths can defer between machines and between
Bazel instances, for example:
This patch adds a post-process to wrapped_clang to normalize those paths
by:
the execution root
use the standard location of Xcode (
/Applications/Xcode.app). Theuser doesn't need to have Xcode installed to this location as Bazel are
already mapping them to the correct location locally.
This makes the produced
.dfiles deterministic and can reliably beshared with the remote cache.
Fixes #11817.