cmd/go: use local state object in env.runEnv

This commit modifies `env.runEnv` 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/envcmd
rf '
  add env.go:/func runEnv\(/-0 var moduleLoaderState *modload.State
  ex {
    import "cmd/go/internal/modload";
    modload.LoaderState -> moduleLoaderState
  }
  add runEnv://+0 moduleLoaderState := modload.NewState()
  rm env.go:/var moduleLoaderState \*modload.State/
'

Change-Id: I1177df5d09a6ee642eade6cfa4278bb1629843a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/711131
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/envcmd/env.go

@@ -272,6 +272,7 @@ func argKey(arg string) string {
 }
 
 func runEnv(ctx context.Context, cmd *base.Command, args []string) {
+	moduleLoaderState := modload.NewState()
 	if *envJson && *envU {
 		base.Fatalf("go: cannot use -json with -u")
 	}
@@ -306,7 +307,7 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 	}
 
 	env := cfg.CmdEnv
-	env = append(env, ExtraEnvVars(modload.LoaderState)...)
+	env = append(env, ExtraEnvVars(moduleLoaderState)...)
 
 	if err := fsys.Init(); err != nil {
 		base.Fatal(err)
@@ -336,8 +337,8 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 		}
 	}
 	if needCostly {
-		work.BuildInit(modload.LoaderState)
-		env = append(env, ExtraEnvVarsCostly(modload.LoaderState)...)
+		work.BuildInit(moduleLoaderState)
+		env = append(env, ExtraEnvVarsCostly(moduleLoaderState)...)
 	}
 
 	if len(args) > 0 {