Add source.pre_release_prefixes

Allow the user to opt into checking for prefixes other than the default
alpha/beta/rc.
Opting in additionally allows for prereleases containing '-' delimeters as
allowed by Semver 2.0.0.

README.md

@@ -111,8 +111,14 @@ differences:
     Note however that variants and pre-releases both use the same syntax:
     `1.2.3-alpine` is technically also valid syntax for a Semver prerelease. For
     this reason, the resource will only consider prerelease data starting with
-    `alpha`, `beta`, or `rc` as a proper prerelease, treating anything else as
-    a variant.
+    `alpha`, `beta`, or `rc` as a proper prerelease, or values provided by
+    `pre_release_prefixes`, treating anything else as a variant.
+    </td>
+  </tr>
+  <tr>
+    <td><code>pre_release_prefixes</code> <em>(Optional)</em></td>
+    <td>
+    Opt in to additional pre-release prefixes (e.g. `build.3`)
     </td>
   </tr>
   <tr>

check_test.go

@@ -854,6 +854,30 @@ var _ = DescribeTable("tracking semver tags",
 			},
 		},
 	),
+	Entry("prerelease prefixes opted in",
+		SemverTagCheckExample{
+			Tags: map[string]string{
+				"1.0.0-alpha.1": "random-0",
+				"1.0.0":         "random-1",
+				"1.2.1-beta.1":  "random-2",
+				"1.2.1":         "random-3",
+				"2.0.0-rc.1":    "random-4",
+				"2.0.0":         "random-5",
+				"2.0.0-build.1": "random-6",
+			},
+			PreReleases: true,
+			PreReleasePrefixes: []string{"build"},
+			Versions: []string{
+				"1.0.0-alpha.1",
+				"1.0.0",
+				"1.2.1-beta.1",
+				"1.2.1",
+				"2.0.0-build.1",
+				"2.0.0-rc.1",
+				"2.0.0",
+			},
+		},
+	),
 	Entry("prereleases do not include 'variants'",
 		SemverTagCheckExample{
 			Tags: map[string]string{
@@ -1032,6 +1056,34 @@ var _ = DescribeTable("tracking semver tags",
 			},
 		},
 	),
+	Entry("opting in to prereleases allows additional '-' suffixes before variant",
+		SemverTagCheckExample{
+			Tags: map[string]string{
+				"1.0.0-build-foo":       "random-1",
+				"1.0.0-rc.1-foo":        "random-2",
+				"1.0.0-alpha.1-foo":     "random-3",
+				"1.0.0-beta.1-foo":      "random-4",
+				"1.0.0-bar-foo":         "random-5",
+				"1.0.0-rc.1-bar-foo":    "random-6",
+				"1.0.0-alpha.1-bar-foo": "random-7",
+				"1.0.0-beta.1-bar-foo":  "random-8",
+			},
+
+			Variant:     "foo",
+			PreReleases: true,
+			PreReleasePrefixes: []string{"build"},
+
+			Versions: []string{
+				"1.0.0-alpha.1-foo",
+				"1.0.0-alpha.1-bar-foo",
+				"1.0.0-beta.1-foo",
+				"1.0.0-beta.1-bar-foo",
+				"1.0.0-build-foo",
+				"1.0.0-rc.1-foo",
+				"1.0.0-rc.1-bar-foo",
+			},
+		},
+	),
 	Entry("tries mirror and falls back on original repository",
 		SemverTagCheckExample{
 			Tags: map[string]string{
@@ -1065,6 +1117,7 @@ type SemverTagCheckExample struct {
 	Tags map[string]string
 
 	PreReleases bool
+	PreReleasePrefixes []string
 	Variant     string
 
 	SemverConstraint string
@@ -1101,10 +1154,11 @@ func (example SemverTagCheckExample) Run() {
 
 	req := resource.CheckRequest{
 		Source: resource.Source{
-			Repository:       repo.Name(),
-			PreReleases:      example.PreReleases,
-			Variant:          example.Variant,
-			SemverConstraint: example.SemverConstraint,
+			Repository:         repo.Name(),
+			PreReleases:        example.PreReleases,
+			PreReleasePrefixes: example.PreReleasePrefixes,
+			Variant:            example.Variant,
+			SemverConstraint:   example.SemverConstraint,
 		},
 	}
 

commands/check.go

@@ -169,14 +169,23 @@ func checkRepository(repo name.Repository, source resource.Source, from *resourc
 					continue
 				}
 
-				// contains additional variant
-				if strings.Contains(pre, "-") {
-					continue
+				preReleasePrefixes := []string{"alpha", "beta", "rc"}
+				if source.PreReleasePrefixes != nil && len(source.PreReleasePrefixes) > 0 {
+					preReleasePrefixes = append(preReleasePrefixes, source.PreReleasePrefixes...)
+				} else {
+					if strings.Contains(pre, "-") {
+						// contains additional variant
+						continue
+					}
 				}
 
-				if !strings.HasPrefix(pre, "alpha") &&
-					!strings.HasPrefix(pre, "beta") &&
-					!strings.HasPrefix(pre, "rc") {
+				match := false
+				for _, prefix := range preReleasePrefixes {
+					if strings.HasPrefix(pre, prefix) {
+						match = true
+					}
+				}
+				if ! match {
 					// additional variant, not a prerelease segment
 					continue
 				}

types.go

@@ -88,8 +88,9 @@ type Source struct {
 
 	Insecure bool `json:"insecure"`
 
-	PreReleases bool   `json:"pre_releases,omitempty"`
-	Variant     string `json:"variant,omitempty"`
+	PreReleases bool `json:"pre_releases,omitempty"`
+	PreReleasePrefixes []string `json:"pre_release_prefixes,omitempty"`
+	Variant string `json:"variant,omitempty"`
 
 	SemverConstraint string `json:"semver_constraint,omitempty"`