internal/versions: fix package to accept go1.21.0-bigcorp

Adds support for suffixes to x/tools copy of go/version.
Brings in go.dev/cl/559796.

Updates golang/go#65061

Change-Id: Iaa0c98a73d8ddd8a42f0c4d3df7d4d79eb7aeb0a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/562838
LUCI-TryBot-Result: Go LUCI <[email protected]>
Run-TryBot: Tim King <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: timothy-king

internal/versions/versions.go

@@ -4,6 +4,8 @@
 
 package versions
 
+import "strings"
+
 // Note: If we use build tags to use go/versions when go >=1.22,
 // we run into go.dev/issue/53737. Under some operations users would see an
 // import of "go/versions" even if they would not compile the file.
@@ -45,6 +47,7 @@ func IsValid(x string) bool { return isValid(stripGo(x)) }
 // stripGo converts from a "go1.21" version to a "1.21" version.
 // If v does not start with "go", stripGo returns the empty string (a known invalid version).
 func stripGo(v string) string {
+	v, _, _ = strings.Cut(v, "-") // strip -bigcorp suffix.
 	if len(v) < 2 || v[:2] != "go" {
 		return ""
 	}

internal/versions/versions_test.go

@@ -20,6 +20,7 @@ func TestIsValid(t *testing.T) {
 		"go0.0", // ??
 		"go1",
 		"go2",
+		"go1.20.0-bigcorp",
 	} {
 		if !versions.IsValid(x) {
 			t.Errorf("expected versions.IsValid(%q) to hold", x)
@@ -40,6 +41,7 @@ func TestIsValid(t *testing.T) {
 		"go1.21.2_2",
 		"go1.21rc_2",
 		"go1.21rc2_",
+		"go1.600+auto",
 	} {
 		if versions.IsValid(x) {
 			t.Errorf("expected versions.IsValid(%q) to not hold", x)
@@ -52,6 +54,7 @@ func TestVersionComparisons(t *testing.T) {
 		x, y string
 		want int
 	}{
+		// All comparisons of go2, go1.21.2, go1.21rc2, go1.21rc2, go1, go0.0, "", bad
 		{"go2", "go2", 0},
 		{"go2", "go1.21.2", +1},
 		{"go2", "go1.21rc2", +1},
@@ -97,6 +100,11 @@ func TestVersionComparisons(t *testing.T) {
 		{"", "", 0},
 		{"", "bad", 0},
 		{"bad", "bad", 0},
+		// Other tests.
+		{"go1.20", "go1.20.0-bigcorp", 0},
+		{"go1.21", "go1.21.0-bigcorp", -1},  // Starting in Go 1.21, patch missing is different from explicit .0.
+		{"go1.21.0", "go1.21.0-bigcorp", 0}, // Starting in Go 1.21, patch missing is different from explicit .0.
+		{"go1.19rc1", "go1.19", -1},
 	} {
 		got := versions.Compare(item.x, item.y)
 		if got != item.want {