cmd/go: 'Access is denied' when renaming module cache directory [1.14 backport]

[gopherbot]

@jayconrod requested issue #36568 to be considered for backport to the next 1.14 minor release.

@gopherbot Please open backport issue for 1.14.

[jayconrod]

CL 221820 mitigates #36568, an issue where antivirus (or a similar program) prevents modules from being extracted into the module cache. That CL makes two changes:

1. os.Rename (the operation that fails) is re-attempted multiple times over 2000 ms. This should make the error less frequent, but doesn't eliminate it entirely.
2. Adds compatibility with a future change, added in CL 221157 but disabled by default, where modules are extracted in place without requiring os.Rename.

CL 221157 is the proper solution for this problem, but it can't be enabled yet because older versions of the Go command (1.14 and earlier) assume that if a module directory is present, it is fully extracted and ready to use. So if Go 1.14 and 1.15 access the same module directory concurrently, 1.14 might see a partially extracted module. CL 221820 prevents that from happening.

The flag in CL 221157 can be flipped safely when 1.14 and older versions are no longer supported and no longer in use. That would probably be true for 1.17.

I'd like to speed up the migration by backporting CL 221820 to 1.14, probably 1.14.2. That would allow us to flip the flag in 1.16.

[networkimprov]

Older releases remain in use well after they're no longer supported, so we should also backport to 1.13. It's possible that many sites will skip 1.14 entirely due to its major runtime changes and bumpy launch.

[jayconrod]

I've just opened #37802 for 1.13 backport.

[gopherbot]

Change https://golang.org/cl/223146 mentions this issue: [release-branch.go1.13] cmd/go: make module zip extraction more robust

[gopherbot]

Change https://golang.org/cl/223147 mentions this issue: [release-branch.go1.14] cmd/go: make module zip extraction more robust

[cagedmantis]

Approved. This is a serious issue without a reasonable workaround.

[gopherbot]

Closed by merging bec8e9c to release-branch.go1.14.