cmd/go: new tag selection logic

The new logic is "use go1 if it's there, otherwise no tag."
Nothing needs to say "I require go1.0.1", and I want to
preserve some flexibility in defining what tags mean.

Right now (before go1.0.1) there is only one possible tag,
"go1", and I'd like to keep it that way.

R=golang-dev, bradfitz, r, adg
CC=golang-dev
https://golang.org/cl/6112060

src/cmd/go/get.go

@@ -335,43 +335,18 @@ var goTag = regexp.MustCompile(
 // Version "goX" (or "goX.Y" or "goX.Y.Z") matches tags of the same form.
 // Version "release.rN" matches tags of the form "go.rN" (N being a floating-point number).
 // Version "weekly.YYYY-MM-DD" matches tags like "go.weekly.YYYY-MM-DD".
+//
+// NOTE(rsc): Eventually we will need to decide on some logic here.
+// For now, there is only "go1".  This matches the docs in go help get.
 func selectTag(goVersion string, tags []string) (match string) {
-	const rPrefix = "release.r"
-	if strings.HasPrefix(goVersion, rPrefix) {
-		p := "go.r"
-		v, err := strconv.ParseFloat(goVersion[len(rPrefix):], 64)
-		if err != nil {
-			return ""
-		}
-		var matchf float64
-		for _, t := range tags {
-			if !strings.HasPrefix(t, p) {
-				continue
-			}
-			tf, err := strconv.ParseFloat(t[len(p):], 64)
-			if err != nil {
-				continue
-			}
-			if matchf < tf && tf <= v {
-				match, matchf = t, tf
-			}
-		}
-	}
-
-	const wPrefix = "weekly."
-	if strings.HasPrefix(goVersion, wPrefix) {
-		p := "go.weekly."
-		v := goVersion[len(wPrefix):]
 	for _, t := range tags {
-			if !strings.HasPrefix(t, p) {
-				continue
-			}
-			if match < t && t[len(p):] <= v {
-				match = t
-			}
+		if t == "go1" {
+			return "go1"
 		}
 	}
+	return ""
 
+	/*
 		if goTag.MatchString(goVersion) {
 			v := goVersion
 			for _, t := range tags {
@@ -385,6 +360,7 @@ func selectTag(goVersion string, tags []string) (match string) {
 		}
 
 		return match
+	*/
 }
 
 // cmpGoVersion returns -1, 0, +1 reporting whether

src/cmd/go/tag_test.go

@@ -50,6 +50,7 @@ var selectTagTests = []struct {
 	version  string
 	selected string
 }{
+	/*
 		{"release.r57", ""},
 		{"release.r58.2", "go.r58.1"},
 		{"release.r59", "go.r59"},
@@ -85,6 +86,8 @@ var selectTagTests = []struct {
 		{"go200000000000", ""},
 		{"go2.", ""},
 		{"go2.0", ""},
+	*/
+	{"anything", "go1"},
 }
 
 func TestSelectTag(t *testing.T) {