goenv: parse patch version, add func Compare to compare two Go version strings

builder/config.go

@@ -43,7 +43,7 @@ func NewConfig(options *compileopts.Options) (*compileopts.Config, error) {
 	// compiled with the latest Go version.
 	// This may be a bit too aggressive: if the newer version doesn't change the
 	// Go language we will most likely be able to compile it.
-	buildMajor, buildMinor, err := goenv.Parse(runtime.Version())
+	buildMajor, buildMinor, _, err := goenv.Parse(runtime.Version())
 	if err != nil {
 		return nil, err
 	}

goenv/version.go

@@ -34,33 +34,64 @@ func GetGorootVersion() (major, minor int, err error) {
 	if err != nil {
 		return 0, 0, err
 	}
-	return Parse(s)
+	major, minor, _, err = Parse(s)
+	return major, minor, err
 }
 
 // Parse parses the Go version (like "go1.3.2") in the parameter and return the
-// major and minor version: 1 and 3 in this example. If there is an error, (0,
-// 0) and an error will be returned.
-func Parse(version string) (major, minor int, err error) {
+// major, minor, and patch version: 1, 3, and 2 in this example.
+// If there is an error, (0, 0, 0) and an error will be returned.
+func Parse(version string) (major, minor, patch int, err error) {
 	if version == "" || version[:2] != "go" {
-		return 0, 0, errors.New("could not parse Go version: version does not start with 'go' prefix")
+		return 0, 0, 0, errors.New("could not parse Go version: version does not start with 'go' prefix")
 	}
 
 	parts := strings.Split(version[2:], ".")
 	if len(parts) < 2 {
-		return 0, 0, errors.New("could not parse Go version: version has less than two parts")
+		return 0, 0, 0, errors.New("could not parse Go version: version has less than two parts")
 	}
 
 	// Ignore the errors, we don't really handle errors here anyway.
 	var trailing string
-	n, err := fmt.Sscanf(version, "go%d.%d%s", &major, &minor, &trailing)
-	if n == 2 && err == io.EOF {
+	n, err := fmt.Sscanf(version, "go%d.%d.%d%s", &major, &minor, &patch, &trailing)
+	if n == 2 {
+		n, err = fmt.Sscanf(version, "go%d.%d%s", &major, &minor, &trailing)
+	}
+	if n >= 2 && err == io.EOF {
 		// Means there were no trailing characters (i.e., not an alpha/beta)
 		err = nil
 	}
 	if err != nil {
-		return 0, 0, fmt.Errorf("failed to parse version: %s", err)
+		return 0, 0, 0, fmt.Errorf("failed to parse version: %s", err)
+	}
+
+	return major, minor, patch, nil
+}
+
+// Compare compares two Go version strings.
+// The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
+// If either a or b is not a valid Go version, it is treated as "go0.0"
+// and compared lexicographically.
+// See [Parse] for more information.
+func Compare(a, b string) int {
+	aMajor, aMinor, aPatch, _ := Parse(a)
+	bMajor, bMinor, bPatch, _ := Parse(b)
+	switch {
+	case aMajor < bMajor:
+		return -1
+	case aMajor > bMajor:
+		return +1
+	case aMinor < bMinor:
+		return -1
+	case aMinor > bMinor:
+		return +1
+	case aPatch < bPatch:
+		return -1
+	case aPatch > bPatch:
+		return +1
+	default:
+		return strings.Compare(a, b)
 	}
-	return
 }
 
 // GorootVersionString returns the version string as reported by the Go

goenv/version_test.go

@@ -0,0 +1,71 @@
+package goenv
+
+import "testing"
+
+func TestParse(t *testing.T) {
+	tests := []struct {
+		v       string
+		major   int
+		minor   int
+		patch   int
+		wantErr bool
+	}{
+		{"", 0, 0, 0, true},
+		{"go", 0, 0, 0, true},
+		{"go1", 0, 0, 0, true},
+		{"go.0", 0, 0, 0, true},
+		{"go1.0", 1, 0, 0, false},
+		{"go1.1", 1, 1, 0, false},
+		{"go1.23", 1, 23, 0, false},
+		{"go1.23.5", 1, 23, 5, false},
+		{"go1.23.5-rc6", 1, 23, 5, false},
+		{"go2.0", 2, 0, 0, false},
+		{"go2.0.15", 2, 0, 15, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.v, func(t *testing.T) {
+			major, minor, patch, err := Parse(tt.v)
+			if err == nil && tt.wantErr {
+				t.Errorf("Parse(%q): expected err != nil", tt.v)
+			}
+			if err != nil && !tt.wantErr {
+				t.Errorf("Parse(%q): expected err == nil", tt.v)
+			}
+			if major != tt.major || minor != tt.minor || patch != tt.patch {
+				t.Errorf("Parse(%q): expected %d, %d, %d, nil; got %d, %d, %d, %v",
+					tt.v, tt.major, tt.minor, tt.patch, major, minor, patch, err)
+			}
+		})
+	}
+}
+
+func TestCompare(t *testing.T) {
+	tests := []struct {
+		a    string
+		b    string
+		want int
+	}{
+		{"", "", 0},
+		{"go0", "go0", 0},
+		{"go0", "go1", -1},
+		{"go1", "go0", 1},
+		{"go1", "go2", -1},
+		{"go2", "go1", 1},
+		{"go1.1", "go1.2", -1},
+		{"go1.2", "go1.1", 1},
+		{"go1.1.0", "go1.2.0", -1},
+		{"go1.2.0", "go1.1.0", 1},
+		{"go1.2.0", "go2.3.0", -1},
+		{"go1.23.2", "go1.23.10", -1},
+		{"go0.1.22", "go1.23.101", -1},
+	}
+	for _, tt := range tests {
+		t.Run(tt.a+" "+tt.b, func(t *testing.T) {
+			got := Compare(tt.a, tt.b)
+			if got != tt.want {
+				t.Errorf("Compare(%q, %q): expected %d; got %d",
+					tt.a, tt.b, tt.want, got)
+			}
+		})
+	}
+}