cmd/go: use local state object in generate.runGenerate

This commit modifies `generate.runGenerate` to construct a new
modload.State object using the new constructor instead of the current
global `modload.LoaderState` variable.

This commit is part of the overall effort to eliminate global
modloader state.

[git-generate]
cd src/cmd/go/internal/generate
rf '
  add generate.go:/func runGenerate\(/-0 var moduleLoaderState *modload.State
  ex {
    import "cmd/go/internal/modload";
    modload.LoaderState -> moduleLoaderState
  }
  add runGenerate://+0 moduleLoaderState := modload.NewState()
  rm generate.go:/var moduleLoaderState \*modload.State/
'

Change-Id: Iea9d662ba47657aa5daa70d32117cdf52fd02b7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/711132
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: jitsu-net

src/cmd/go/internal/generate/generate.go

@@ -182,7 +182,8 @@ func init() {
 }
 
 func runGenerate(ctx context.Context, cmd *base.Command, args []string) {
-	modload.InitWorkfile(modload.LoaderState)
+	moduleLoaderState := modload.NewState()
+	modload.InitWorkfile(moduleLoaderState)
 
 	if generateRunFlag != "" {
 		var err error
@@ -204,8 +205,8 @@ func runGenerate(ctx context.Context, cmd *base.Command, args []string) {
 	// Even if the arguments are .go files, this loop suffices.
 	printed := false
 	pkgOpts := load.PackageOpts{IgnoreImports: true}
-	for _, pkg := range load.PackagesAndErrors(modload.LoaderState, ctx, pkgOpts, args) {
-		if modload.Enabled(modload.LoaderState) && pkg.Module != nil && !pkg.Module.Main {
+	for _, pkg := range load.PackagesAndErrors(moduleLoaderState, ctx, pkgOpts, args) {
+		if modload.Enabled(moduleLoaderState) && pkg.Module != nil && !pkg.Module.Main {
 			if !printed {
 				fmt.Fprintf(os.Stderr, "go: not generating in packages in dependency modules\n")
 				printed = true