stack: make stdlib src link work even on devel Go build

Process the development Go version to extract the git commit and use
this as a reference. Obviously this won't work if the commit is not
upstream but for people testing public code, this may be useful.

Make unit test pass on non-release Go build.

Author: maruel

internal/internaltest/internaltest.go

@@ -148,7 +148,7 @@ var (
 // Ignores the revision (go1.<minor>.<revision>).
 func GetGoMinorVersion() int {
 	ver := runtime.Version()
-	if strings.HasPrefix(ver, "devel ") {
+	if strings.HasPrefix(ver, "devel +") {
 		return 0
 	}
 	if !strings.HasPrefix(ver, "go1.") {

stack/html.go

@@ -134,7 +134,12 @@ func getSrcBranchURL(c *Call) (template.URL, template.URL) {
 	if c.Location == Stdlib {
 		// TODO(maruel): This is not strictly speaking correct. The remote could be
 		// running a different Go version from the current executable.
-		tag = url.QueryEscape(runtime.Version())
+		ver := runtime.Version()
+		const devel = "devel +"
+		if strings.HasPrefix(ver, devel) {
+			ver = ver[len(devel) : len(devel)+10]
+		}
+		tag = url.QueryEscape(ver)
 		return template.URL(fmt.Sprintf("https://github.com/golang/go/blob/%s/src/%s#L%d", tag, escape(c.RelSrcPath), c.Line)), template.URL(tag)
 	}
 	// TODO(maruel): Leverage Location.

stack/html_test.go

@@ -10,6 +10,7 @@ import (
 	"html/template"
 	"io"
 	"io/ioutil"
+	"net/url"
 	"regexp"
 	"runtime"
 	"strings"
@@ -81,6 +82,11 @@ func TestGenerate(t *testing.T) {
 func TestGetSrcBranchURL(t *testing.T) {
 	t.Parallel()
 	ver := runtime.Version()
+	const prefix = "devel +"
+	if strings.HasPrefix(ver, prefix) {
+		ver = ver[len(prefix) : len(prefix)+10]
+	}
+	ver = url.QueryEscape(ver)
 	data := []struct {
 		name        string
 		c           Call