cmd/go, cmd/compile: use Windows response files to avoid arg length limits

Fixes #18468

Change-Id: Ic88a8daf67db949e5b59f9aa466b37e7f7890713
Reviewed-on: https://go-review.googlesource.com/110395
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/src/cmd/internal/objabi/flag.go b/src/cmd/internal/objabi/flag.go
index ecb9e39a6b..30cd7dccac 100644
--- a/src/cmd/internal/objabi/flag.go
+++ b/src/cmd/internal/objabi/flag.go
@@ -8,6 +8,8 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"io/ioutil"
+	"log"
 	"os"
 	"strconv"
 	"strings"
@@ -28,9 +30,46 @@ func Flagprint(w io.Writer) {
 
 func Flagparse(usage func()) {
 	flag.Usage = usage
+	os.Args = expandArgs(os.Args)
 	flag.Parse()
 }
 
+// expandArgs expands "response files" arguments in the provided slice.
+//
+// A "response file" argument starts with '@' and the rest of that
+// argument is a filename with CR-or-CRLF-separated arguments. Each
+// argument in the named files can also contain response file
+// arguments. See Issue 18468.
+//
+// The returned slice 'out' aliases 'in' iff the input did not contain
+// any response file arguments.
+//
+// TODO: handle relative paths of recursive expansions in different directories?
+// Is there a spec for this? Are relative paths allowed?
+func expandArgs(in []string) (out []string) {
+	// out is nil until we see a "@" argument.
+	for i, s := range in {
+		if strings.HasPrefix(s, "@") {
+			if out == nil {
+				out = make([]string, 0, len(in)*2)
+				out = append(out, in[:i]...)
+			}
+			slurp, err := ioutil.ReadFile(s[1:])
+			if err != nil {
+				log.Fatal(err)
+			}
+			args := strings.Split(strings.TrimSpace(strings.Replace(string(slurp), "\r", "", -1)), "\n")
+			out = append(out, expandArgs(args)...)
+		} else if out != nil {
+			out = append(out, s)
+		}
+	}
+	if out == nil {
+		return in
+	}
+	return
+}
+
 func AddVersionFlag() {
 	flag.Var(versionFlag{}, "V", "print version and exit")
 }