goenv: add Compare function to compare two Go version strings

Author: ydnar

goenv/version.go

@@ -74,6 +74,28 @@ func WantGoVersion(s string, major, minor int) bool {
 	return ma > major || (ma == major && mi >= minor)
 }
 
+// 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, _ := Parse(a)
+	bMajor, bMinor, _ := Parse(b)
+	switch {
+	case aMajor < bMajor:
+		return -1
+	case aMajor > bMajor:
+		return +1
+	case aMinor < bMinor:
+		return -1
+	case aMinor > bMinor:
+		return +1
+	default:
+		return strings.Compare(a, b)
+	}
+}
+
 // GorootVersionString returns the version string as reported by the Go
 // toolchain. It is usually of the form `go1.x.y` but can have some variations
 // (for beta releases, for example).

goenv/version_test.go

@@ -66,3 +66,33 @@ func TestWantGoVersion(t *testing.T) {
 		})
 	}
 }
+
+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}, // FIXME: parse patch number
+	}
+	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)
+			}
+		})
+	}
+}