dist: generate stub go.mod in workdir

...and run commands from there.

This removes the requirement that bootstrap must not run inside a module
by ensuring that enclosing modules do not interfere with bootstrap.

Fixes #44209.

Change-Id: I700a81829226770b8160c8ff04127b855b6e26bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/296610
Trust: Jay Conrod <jayconrod@google.com>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 07ede42574f46cc40717880645db16bd3c6fd483..158cedbadc4e390d3728648b7ed06849255f8719 100644 (file)
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -111,9 +111,6 @@ func xinit() {
                fatalf("$GOROOT must be set")
        }
        goroot = filepath.Clean(b)
-       if modRoot := findModuleRoot(goroot); modRoot != "" {
-               fatalf("found go.mod file in %s: $GOROOT must not be inside a module", modRoot)
-       }
 
        b = os.Getenv("GOROOT_FINAL")
        if b == "" {
@@ -241,6 +238,9 @@ func xinit() {
        os.Setenv("LANGUAGE", "en_US.UTF8")
 
        workdir = xworkdir()
+       if err := ioutil.WriteFile(pathf("%s/go.mod", workdir), []byte("module bootstrap"), 0666); err != nil {
+               fatalf("cannot write stub go.mod: %s", err)
+       }
        xatexit(rmworkdir)
 
        tooldir = pathf("%s/pkg/tool/%s_%s", goroot, gohostos, gohostarch)
@@ -1505,11 +1505,11 @@ func goCmd(goBinary string, cmd string, args ...string) {
                goCmd = append(goCmd, "-p=1")
        }
 
-       run(goroot, ShowOutput|CheckExit, append(goCmd, args...)...)
+       run(workdir, ShowOutput|CheckExit, append(goCmd, args...)...)
 }
 
 func checkNotStale(goBinary string, targets ...string) {
-       out := run(goroot, CheckExit,
+       out := run(workdir, CheckExit,
                append([]string{
                        goBinary,
                        "list", "-gcflags=all=" + gogcflags, "-ldflags=all=" + goldflags,
@@ -1519,7 +1519,7 @@ func checkNotStale(goBinary string, targets ...string) {
                os.Setenv("GODEBUG", "gocachehash=1")
                for _, target := range []string{"runtime/internal/sys", "cmd/dist", "cmd/link"} {
                        if strings.Contains(out, "STALE "+target) {
-                               run(goroot, ShowOutput|CheckExit, goBinary, "list", "-f={{.ImportPath}} {{.Stale}}", target)
+                               run(workdir, ShowOutput|CheckExit, goBinary, "list", "-f={{.ImportPath}} {{.Stale}}", target)
                                break
                        }
                }
@@ -1615,20 +1615,6 @@ func checkCC() {
        }
 }
 
-func findModuleRoot(dir string) (root string) {
-       for {
-               if fi, err := os.Stat(filepath.Join(dir, "go.mod")); err == nil && !fi.IsDir() {
-                       return dir
-               }
-               d := filepath.Dir(dir)
-               if d == dir {
-                       break
-               }
-               dir = d
-       }
-       return ""
-}
-
 func defaulttarg() string {
        // xgetwd might return a path with symlinks fully resolved, and if
        // there happens to be symlinks in goroot, then the hasprefix test