Extract functions AddCoAuthorToMessage and AddCoAuthorToDescription

In this commit we only need the former; the latter will be reused later in this
branch.

Author: stefanhaller

pkg/commands/git_commands/commit.go

@@ -39,13 +39,13 @@ func (self *CommitCommands) SetAuthor(value string) error {
 }
 
 // Add a commit's coauthor using Github/Gitlab Co-authored-by metadata. Value is expected to be of the form 'Name <Email>'
-func (self *CommitCommands) AddCoAuthor(sha string, value string) error {
+func (self *CommitCommands) AddCoAuthor(sha string, author string) error {
 	message, err := self.GetCommitMessage(sha)
 	if err != nil {
 		return err
 	}
 
-	message = message + fmt.Sprintf("\nCo-authored-by: %s", value)
+	message = AddCoAuthorToMessage(message, author)
 
 	cmdArgs := NewGitCmd("commit").
 		Arg("--allow-empty", "--amend", "--only", "-m", message).
@@ -54,6 +54,25 @@ func (self *CommitCommands) AddCoAuthor(sha string, value string) error {
 	return self.cmd.New(cmdArgs).Run()
 }
 
+func AddCoAuthorToMessage(message string, author string) string {
+	subject, body, _ := strings.Cut(message, "\n")
+
+	return strings.TrimSpace(subject) + "\n\n" + AddCoAuthorToDescription(strings.TrimSpace(body), author)
+}
+
+func AddCoAuthorToDescription(description string, author string) string {
+	if description != "" {
+		lines := strings.Split(description, "\n")
+		if strings.HasPrefix(lines[len(lines)-1], "Co-authored-by:") {
+			description += "\n"
+		} else {
+			description += "\n\n"
+		}
+	}
+
+	return description + fmt.Sprintf("Co-authored-by: %s", author)
+}
+
 // ResetToCommit reset to commit
 func (self *CommitCommands) ResetToCommit(sha string, strength string, envVars []string) error {
 	cmdArgs := NewGitCmd("reset").Arg("--"+strength, sha).ToArgv()

pkg/commands/git_commands/commit_test.go

@@ -333,3 +333,70 @@ func TestGetCommitMessageFromHistory(t *testing.T) {
 		})
 	}
 }
+
+func TestAddCoAuthorToMessage(t *testing.T) {
+	scenarios := []struct {
+		name           string
+		message        string
+		expectedResult string
+	}{
+		{
+			// This never happens, I think it isn't possible to create a commit
+			// with an empty message. Just including it for completeness.
+			name:           "Empty message",
+			message:        "",
+			expectedResult: "\n\nCo-authored-by: John Doe <[email protected]>",
+		},
+		{
+			name:           "Just a subject, no body",
+			message:        "Subject",
+			expectedResult: "Subject\n\nCo-authored-by: John Doe <[email protected]>",
+		},
+		{
+			name:           "Subject and body",
+			message:        "Subject\n\nBody",
+			expectedResult: "Subject\n\nBody\n\nCo-authored-by: John Doe <[email protected]>",
+		},
+		{
+			name:           "Body already ending with a Co-authored-by line",
+			message:        "Subject\n\nBody\n\nCo-authored-by: Jane Smith <[email protected]>",
+			expectedResult: "Subject\n\nBody\n\nCo-authored-by: Jane Smith <[email protected]>\nCo-authored-by: John Doe <[email protected]>",
+		},
+	}
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			result := AddCoAuthorToMessage(s.message, "John Doe <[email protected]>")
+			assert.Equal(t, s.expectedResult, result)
+		})
+	}
+}
+
+func TestAddCoAuthorToDescription(t *testing.T) {
+	scenarios := []struct {
+		name           string
+		description    string
+		expectedResult string
+	}{
+		{
+			name:           "Empty description",
+			description:    "",
+			expectedResult: "Co-authored-by: John Doe <[email protected]>",
+		},
+		{
+			name:           "Non-empty description",
+			description:    "Body",
+			expectedResult: "Body\n\nCo-authored-by: John Doe <[email protected]>",
+		},
+		{
+			name:           "Description already ending with a Co-authored-by line",
+			description:    "Body\n\nCo-authored-by: Jane Smith <[email protected]>",
+			expectedResult: "Body\n\nCo-authored-by: Jane Smith <[email protected]>\nCo-authored-by: John Doe <[email protected]>",
+		},
+	}
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			result := AddCoAuthorToDescription(s.description, "John Doe <[email protected]>")
+			assert.Equal(t, s.expectedResult, result)
+		})
+	}
+}

pkg/integration/tests/commit/add_co_author.go

@@ -34,6 +34,7 @@ var AddCoAuthor = NewIntegrationTest(NewIntegrationTestArgs{
 
 		t.Views().Main().ContainsLines(
 			Equals("    initial commit"),
+			Equals("    "),
 			Equals("    Co-authored-by: John Smith <[email protected]>"),
 		)
 	},