Include ability to add tag_prefix

Signed-off-by: Zachary Gershman <zgershman@pivotal.io>

README.md

@@ -91,6 +91,9 @@ matching the patterns in `globs` to the release.
 * `tag`: *Required.* A path to a file containing the name of the Git tag to use
   for the release.
 
+* `tag_prefix`: *Optional.*  If specified, the tag read from the file will be
+prepended with this string. This is useful for adding v in front of version numbers.
+
 * `commitish`: *Optional.* A path to a file containing the commitish (SHA, tag,
   branch name) that the release should be associated with.
 

out_command.go

@@ -36,6 +36,8 @@ func (c *OutCommand) Run(sourceDir string, request OutRequest) (OutResponse, err
 		return OutResponse{}, err
 	}
 
+	tag = request.Params.TagPrefix + tag
+
 	var body string
 	bodySpecified := false
 	if request.Params.BodyPath != "" {

out_command_test.go

@@ -347,5 +347,31 @@ var _ = Describe("Out Command", func() {
 				Ω(err).Should(MatchError("could not find file that matches glob '*.gif'"))
 			})
 		})
+
+		Context("when the tag_prefix is set", func() {
+			BeforeEach(func() {
+				namePath := filepath.Join(sourcesDir, "name")
+				tagPath := filepath.Join(sourcesDir, "tag")
+
+				file(namePath, "v0.3.12")
+				file(tagPath, "0.3.12")
+
+				request = resource.OutRequest{
+					Params: resource.OutParams{
+						NamePath:  "name",
+						TagPath:   "tag",
+						TagPrefix: "version-",
+					},
+				}
+			})
+
+			It("appends the TagPrefix onto the TagName", func() {
+				Ω(githubClient.CreateReleaseCallCount()).Should(Equal(1))
+				release := githubClient.CreateReleaseArgsForCall(0)
+
+				Ω(*release.Name).Should(Equal("v0.3.12"))
+				Ω(*release.TagName).Should(Equal("version-0.3.12"))
+			})
+		})
 	})
 })

resources.go

@@ -41,6 +41,7 @@ type OutParams struct {
 	BodyPath      string `json:"body"`
 	TagPath       string `json:"tag"`
 	CommitishPath string `json:"commitish"`
+	TagPrefix     string `json:"tag_prefix"`
 
 	Globs []string `json:"globs"`
 }