feat: add ability to compare semver versions (#2047)

Towards #2041

It's possible the configured value in config.yaml is too old. We will
need to be able to compare 2 semver strings.

Author: chingor13

internal/semver/semver.go

@@ -91,6 +91,51 @@ func Parse(versionString string) (*Version, error) {
 	return v, nil
 }
 
+// Compare returns an integer comparing two versions.
+// The result is -1, 0, or 1 depending on whether v is less than, equal to, or greater than other.
+func (v *Version) Compare(other *Version) int {
+	if v.Major < other.Major {
+		return -1
+	}
+	if v.Major > other.Major {
+		return 1
+	}
+	if v.Minor < other.Minor {
+		return -1
+	}
+	if v.Minor > other.Minor {
+		return 1
+	}
+	if v.Patch < other.Patch {
+		return -1
+	}
+	if v.Patch > other.Patch {
+		return 1
+	}
+	// a pre-release version is less than a non-pre-release version
+	if v.Prerelease != "" && other.Prerelease == "" {
+		return -1
+	}
+	if v.Prerelease == "" && other.Prerelease != "" {
+		return 1
+	}
+	// lexical comparison between prerelease type (e.g. "alpha" vs "beta")
+	if v.Prerelease < other.Prerelease {
+		return -1
+	}
+	if v.Prerelease > other.Prerelease {
+		return 1
+	}
+	// prerelease number (e.g. "alpha1" vs "alpha2")
+	if v.PrereleaseNumber < other.PrereleaseNumber {
+		return -1
+	}
+	if v.PrereleaseNumber > other.PrereleaseNumber {
+		return 1
+	}
+	return 0
+}
+
 // String formats a Version struct into a string.
 func (v *Version) String() string {
 	version := fmt.Sprintf("%d.%d.%d", v.Major, v.Minor, v.Patch)

internal/semver/semver_test.go

@@ -241,3 +241,148 @@ func TestDeriveNext(t *testing.T) {
 		})
 	}
 }
+
+func TestCompare(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		versionA string
+		versionB string
+		want     int
+	}{
+		{
+			name:     "equal",
+			versionA: "1.2.3",
+			versionB: "1.2.3",
+			want:     0,
+		},
+		{
+			name:     "equal with pre-release",
+			versionA: "1.2.3-alpha",
+			versionB: "1.2.3-alpha",
+			want:     0,
+		},
+		{
+			name:     "equal with pre-release and number",
+			versionA: "1.2.3-alpha4",
+			versionB: "1.2.3-alpha4",
+			want:     0,
+		},
+		{
+			name:     "equal with pre-release and number, different separator",
+			versionA: "1.2.3-alpha4",
+			versionB: "1.2.3-alpha.4",
+			want:     0,
+		},
+		{
+			name:     "less than patch",
+			versionA: "1.2.3",
+			versionB: "1.2.4",
+			want:     -1,
+		},
+		{
+			name:     "less than minor",
+			versionA: "1.2.3",
+			versionB: "1.3.0",
+			want:     -1,
+		},
+		{
+			name:     "less than major",
+			versionA: "1.2.3",
+			versionB: "2.0.0",
+			want:     -1,
+		},
+		{
+			name:     "less than prerelease",
+			versionA: "1.2.3-alpha",
+			versionB: "1.2.3-beta",
+			want:     -1,
+		},
+		{
+			name:     "less than prerelease number",
+			versionA: "1.2.3-alpha1",
+			versionB: "1.2.3-alpha2",
+			want:     -1,
+		},
+		{
+			name:     "less than prerelease number with separator",
+			versionA: "1.2.3-alpha.1",
+			versionB: "1.2.3-alpha.2",
+			want:     -1,
+		},
+		{
+			name:     "less than prerelease against stable",
+			versionA: "1.2.3-alpha1",
+			versionB: "1.2.3",
+			want:     -1,
+		},
+		{
+			name:     "less than prerelease without number",
+			versionA: "1.2.3-alpha",
+			versionB: "1.2.3-alpha1",
+			want:     -1,
+		},
+		{
+			name:     "greater than patch",
+			versionA: "1.2.4",
+			versionB: "1.2.3",
+			want:     1,
+		},
+		{
+			name:     "greater than minor",
+			versionA: "1.3.0",
+			versionB: "1.2.3",
+			want:     1,
+		},
+		{
+			name:     "greater than major",
+			versionA: "2.0.0",
+			versionB: "1.2.3",
+			want:     1,
+		},
+		{
+			name:     "greater than prerelease",
+			versionA: "1.2.3-beta",
+			versionB: "1.2.3-alpha",
+			want:     1,
+		},
+		{
+			name:     "greater than prerelease number",
+			versionA: "1.2.3-alpha2",
+			versionB: "1.2.3-alpha1",
+			want:     1,
+		},
+		{
+			name:     "greater than prerelease number with separator",
+			versionA: "1.2.3-alpha.2",
+			versionB: "1.2.3-alpha.1",
+			want:     1,
+		},
+		{
+			name:     "greater than prerelease against stable",
+			versionA: "1.2.3",
+			versionB: "1.2.3-alpha1",
+			want:     1,
+		},
+		{
+			name:     "greater than prerelease without number",
+			versionA: "1.2.3-alpha1",
+			versionB: "1.2.3-alpha",
+			want:     1,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			a, err := Parse(test.versionA)
+			if err != nil {
+				t.Fatalf("Parse() returned an error: %v", err)
+			}
+			b, err := Parse(test.versionB)
+			if err != nil {
+				t.Fatalf("Parse() returned an error: %v", err)
+			}
+			got := a.Compare(b)
+			if diff := cmp.Diff(test.want, got); diff != "" {
+				t.Errorf("TestCompare() returned diff (-want +got):\n%s", diff)
+			}
+		})
+	}
+}