From a coworker's report:
If you build Chromium on Windows and run Visual Studio with VS-Chromium extension you may start seeing some seemingly random 'permission denied' errors during the build now that clang-cl is the default compiler.
This was investigated with PROCMON and it appears that the VS Chromium extension scans the source tree during the build and ends up reading temporary obj files created by clang.
Here are a few examples of files that can cause problems:
Because VS-Chromium doesn't recognize the file extensions it doesn't realize that these are files that should be excluded from scanning so it scans them, thus briefly holding a lock on them, thus causing build failures.
The workaround is to modify vs-chromium-project.txt to exclude .obj and .pch instead of *.obj and *.pch. This is easy enough for those who already have a vs-chromium-project.txt file, but tricky for others since creating such a file overrides the default filters and therefore can cause new problems. A workable vs-chromium-project.txt file with these modifications is attached - drop that in src\chromium\src to reconfigure VS-Chromium.
Building in these new filters would be very helpful.