cmd/go/internal/modfetch: consolidate global vars

cmd/go/internal/modfetch: consolidate global vars

This commit conslidates global variables represeting the current
modfetch state into a single variable in preparation for injection via
the rsc.io/rf tool.

This commit is part of the larger effort to eliminate global module
loader state.

[git-generate]
cd src/cmd/go/internal/modfetch
rf '
  add State func NewState() *State {\
    s := new(State)\
    s.lookupCache = new(par.Cache[lookupCacheKey, Repo])\
    s.downloadCache = new(par.ErrCache[module.Version, string])\
    return s\
  }

  add State var ModuleFetchState *State = NewState()

  mv State.goSumFile State.GoSumFile
  add State:/^[[:space:]]*GoSumFile /-0 // path to go.sum; set by package modload
  ex {
    GoSumFile -> ModuleFetchState.GoSumFile
  }

  mv State.workspaceGoSumFiles State.WorkspaceGoSumFiles
  add State:/^[[:space:]]*WorkspaceGoSumFiles /-0 // path to module go.sums in workspace; set by package modload
  ex {
    WorkspaceGoSumFiles -> ModuleFetchState.WorkspaceGoSumFiles
  }

  add State:/^[[:space:]]*lookupCache /-0 // The Lookup cache is used cache the work done by Lookup.\
      // It is important that the global functions of this package that access it do not\
      // do so after they return.
  add State:/^[[:space:]]*downloadCache /-0 // The downloadCache is used to cache the operation of downloading a module to disk\
      // (if it'\\\''s not already downloaded) and getting the directory it was downloaded to.\
      // It is important that downloadCache must not be accessed by any of the exported\
      // functions of this package after they return, because it can be modified by the\
      // non-thread-safe SetState function.
  add State:/^[[:space:]]*downloadCache.*$/ // version → directory;
  ex {
    lookupCache -> ModuleFetchState.lookupCache
    downloadCache -> ModuleFetchState.downloadCache
  }
  rm 'lookupCache'
  rm 'downloadCache'
'

for dir in modload ; do
  cd ../${dir}
  rf '
    ex {
      import "cmd/go/internal/modfetch"
      modfetch.GoSumFile -> modfetch.ModuleFetchState.GoSumFile
      modfetch.WorkspaceGoSumFiles -> modfetch.ModuleFetchState.WorkspaceGoSumFiles
    }
  '
done

cd ../modfetch
rf '
  rm GoSumFile
  rm WorkspaceGoSumFiles
'

Change-Id: Iaa0f8a40192127457a539120eb94337940cb8d4a
Reviewed-on: https://go-review.googlesource.com/c/go/+/719700
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Michael Matloob <matloob@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>