cmd/doc: better support for no network

Allow skipping the deprecation check when GOPROXY=off. The deprecation
check is an informational message so this doesn't affect the success of
the command. We should probably skip the check in more cases when
GOPROXY=off but that's a bigger change that should be made in a later
release.

There are still some deps.dev log messages that we should try to
suppress.

For #68106

Change-Id: Ifa0efd01ed623bb68c7ad7c5cfb6705547d157a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/675155
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Matloob <matloob@google.com>
Reviewed-by: Michael Matloob <matloob@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>

src/cmd/doc/main.go

@@ -259,10 +259,18 @@ func doPkgsite(urlPath string) error {
 	signal.Ignore(signalsToIgnore...)
 
 	const version = "v0.0.0-20250520201116-40659211760d"
-	cmd := exec.Command("go", "run", "golang.org/x/pkgsite/cmd/internal/doc@"+version,
+	docatversion := "golang.org/x/pkgsite/cmd/internal/doc@" + version
+	// First download the module and then try to run with GOPROXY=off to circumvent
+	// the deprecation check. This will allow the pkgsite command to run if it's
+	// in the module cache but there's no network.
+	if _, err := runCmd(nil, "go", "mod", "download", docatversion); err != nil {
+		return err
+	}
+	cmd := exec.Command("go", "run", docatversion,
 		"-gorepo", buildCtx.GOROOT,
 		"-http", addr,
 		"-open", path)
+	cmd.Env = append(os.Environ(), "GOPROXY=off")
 	cmd.Stdout = os.Stderr
 	cmd.Stderr = os.Stderr
 

src/cmd/go/internal/load/pkg.go

@@ -3410,7 +3410,7 @@ func PackagesAndErrorsOutsideModule(ctx context.Context, opts PackageOpts, args
 	}
 	rootMod := qrs[0].Mod
 	deprecation, err := modload.CheckDeprecation(ctx, rootMod)
-	if err != nil {
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
 		return nil, fmt.Errorf("%s: %w", args[0], err)
 	}
 	if deprecation != "" {