cmd/dist: only test SWIG if we have a new enough version

Fixes #22858

Change-Id: I0478d5609e381f01c7345e7f53c24af05d7f78ad
Reviewed-on: https://go-review.googlesource.com/82415
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/dist/test.go

@@ -583,7 +583,7 @@ func (t *tester) registerTests() {
 				},
 			})
 		}
-		if swig, _ := exec.LookPath("swig"); swig != "" && goos != "android" {
+		if t.hasSwig() && goos != "android" {
 			t.tests = append(t.tests, distTest{
 				name:    "swig_stdio",
 				heading: "../misc/swig/stdio",
@@ -1197,6 +1197,63 @@ func (t *tester) hasBash() bool {
 	return true
 }
 
+func (t *tester) hasSwig() bool {
+	swig, err := exec.LookPath("swig")
+	if err != nil {
+		return false
+	}
+	out, err := exec.Command(swig, "-version").CombinedOutput()
+	if err != nil {
+		return false
+	}
+
+	re := regexp.MustCompile(`[vV]ersion +([\d]+)([.][\d]+)?([.][\d]+)?`)
+	matches := re.FindSubmatch(out)
+	if matches == nil {
+		// Can't find version number; hope for the best.
+		return true
+	}
+
+	major, err := strconv.Atoi(string(matches[1]))
+	if err != nil {
+		// Can't find version number; hope for the best.
+		return true
+	}
+	if major < 3 {
+		return false
+	}
+	if major > 3 {
+		// 4.0 or later
+		return true
+	}
+
+	// We have SWIG version 3.x.
+	if len(matches[2]) > 0 {
+		minor, err := strconv.Atoi(string(matches[2][1:]))
+		if err != nil {
+			return true
+		}
+		if minor > 0 {
+			// 3.1 or later
+			return true
+		}
+	}
+
+	// We have SWIG version 3.0.x.
+	if len(matches[3]) > 0 {
+		patch, err := strconv.Atoi(string(matches[3][1:]))
+		if err != nil {
+			return true
+		}
+		if patch < 6 {
+			// Before 3.0.6.
+			return false
+		}
+	}
+
+	return true
+}
+
 func (t *tester) raceDetectorSupported() bool {
 	switch gohostos {
 	case "linux", "darwin", "freebsd", "windows":