cmd/go/internal/imports: make Tags and AnyTags safe for concurrent use

AnyTags turned up as a data race while running 'go test -race cmd/go'.
I'm not sure how long the race has been present.

==================
WARNING: DATA RACE
Read at 0x000001141ec0 by goroutine 8:
  cmd/go/internal/imports.AnyTags()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/imports/tags.go:45 +0x10e
  cmd/go/internal/modload.QueryPattern.func2()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:539 +0x11d
  cmd/go/internal/modload.QueryPattern.func4.1()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:607 +0x3db
  cmd/go/internal/modload.queryPrefixModules.func1()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:677 +0xa7

Previous write at 0x000001141ec0 by goroutine 7:
  cmd/go/internal/imports.AnyTags()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/imports/tags.go:46 +0x26b
  cmd/go/internal/modload.QueryPattern.func2()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:539 +0x11d
  cmd/go/internal/modload.QueryPattern.func4.1()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:607 +0x3db
  cmd/go/internal/modload.queryPrefixModules.func1()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:677 +0xa7

Goroutine 8 (running) created at:
  cmd/go/internal/modload.queryPrefixModules()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:676 +0x284
  cmd/go/internal/modload.QueryPattern.func4()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:624 +0x2e4
  cmd/go/internal/modfetch.TryProxies()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modfetch/proxy.go:220 +0x107
  cmd/go/internal/modload.QueryPattern()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:590 +0x69e
  cmd/go/internal/work.installOutsideModule()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/work/build.go:744 +0x4b0
  cmd/go/internal/work.runInstall()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/work/build.go:556 +0x217
  main.main()
      /usr/local/google/home/bcmills/go/src/cmd/go/main.go:194 +0xb94

Goroutine 7 (finished) created at:
  cmd/go/internal/modload.queryPrefixModules()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:676 +0x284
  cmd/go/internal/modload.QueryPattern.func4()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:624 +0x2e4
  cmd/go/internal/modfetch.TryProxies()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modfetch/proxy.go:220 +0x107
  cmd/go/internal/modload.QueryPattern()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/modload/query.go:590 +0x69e
  cmd/go/internal/work.installOutsideModule()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/work/build.go:744 +0x4b0
  cmd/go/internal/work.runInstall()
      /usr/local/google/home/bcmills/go/src/cmd/go/internal/work/build.go:556 +0x217
  main.main()
      /usr/local/google/home/bcmills/go/src/cmd/go/main.go:194 +0xb94
==================

Change-Id: Id394978fd6ea0c30614caf8f90ee4f8e2d272843
Reviewed-on: https://go-review.googlesource.com/c/go/+/265278
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
1 file changed
tree: 6e23058b36d4b7dd621f4a5fc892439edaf5d3f8
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. AUTHORS
  11. CONTRIBUTING.md
  12. CONTRIBUTORS
  13. favicon.ico
  14. LICENSE
  15. PATENTS
  16. README.md
  17. robots.txt
  18. SECURITY.md
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