util/cmpver: move into OSS from corp repo.

Signed-off-by: David Anderson <danderson@tailscale.com>

util/cmpver/version_test.go

@@ -0,0 +1,106 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cmpver
+
+import "testing"
+
+func TestCompare(t *testing.T) {
+	tests := []struct {
+		name   string
+		v1, v2 string
+		want   int
+	}{
+		{
+			name: "both empty",
+			want: 0,
+		},
+		{
+			name: "v1 empty",
+			v2:   "1.2.3",
+			want: -1,
+		},
+		{
+			name: "v2 empty",
+			v1:   "1.2.3",
+			want: 1,
+		},
+
+		{
+			name: "semver major",
+			v1:   "2.0.0",
+			v2:   "1.9.9",
+			want: 1,
+		},
+		{
+			name: "semver major",
+			v1:   "2.0.0",
+			v2:   "1.9.9",
+			want: 1,
+		},
+		{
+			name: "semver minor",
+			v1:   "1.9.0",
+			v2:   "1.8.9",
+			want: 1,
+		},
+		{
+			name: "semver patch",
+			v1:   "1.9.9",
+			v2:   "1.9.8",
+			want: 1,
+		},
+		{
+			name: "semver equal",
+			v1:   "1.9.8",
+			v2:   "1.9.8",
+			want: 0,
+		},
+
+		{
+			name: "tailscale major",
+			v1:   "1.0-0",
+			v2:   "0.97-105",
+			want: 1,
+		},
+		{
+			name: "tailscale minor",
+			v1:   "0.98-0",
+			v2:   "0.97-105",
+			want: 1,
+		},
+		{
+			name: "tailscale patch",
+			v1:   "0.97-120",
+			v2:   "0.97-105",
+			want: 1,
+		},
+		{
+			name: "tailscale equal",
+			v1:   "0.97-105",
+			v2:   "0.97-105",
+			want: 0,
+		},
+		{
+			name: "tailscale weird extra field",
+			v1:   "0.96.1-0", // more fields == larger
+			v2:   "0.96-105",
+			want: 1,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := Compare(test.v1, test.v2)
+			if got != test.want {
+				t.Errorf("Compare(%v, %v) = %v, want %v", test.v1, test.v2, got, test.want)
+			}
+			// Reversing the comparison should reverse the outcome.
+			got2 := Compare(test.v2, test.v1)
+			if got2 != -test.want {
+				t.Errorf("Compare(%v, %v) = %v, want %v", test.v2, test.v1, got2, -test.want)
+			}
+		})
+	}
+}