pkg/commands: Don't duplicate line breaks when retrieving commit message

When using the "copy commit message to clipboard" action, the message will end
up in the clipboard with duplicate line breaks. The same issue also affects the
"Reword Commit" command. GetCommitMessage(), the function used to retrieve the
commit message first splits the output returned by git into separate lines -
without removing the line breaks. After removing the first line (which contains
the commit SHA), it joins the lines of the message itself back together - adding
a second set of line breaks along the way. Stop this from happening.

Fixes #1808.

pkg/commands/git_commands/commit.go

@@ -70,7 +70,7 @@ func (self *CommitCommands) GetHeadCommitMessage() (string, error) {
 func (self *CommitCommands) GetCommitMessage(commitSha string) (string, error) {
 	cmdStr := "git rev-list --format=%B --max-count=1 " + commitSha
 	messageWithHeader, err := self.cmd.New(cmdStr).DontLog().RunWithOutput()
-	message := strings.Join(strings.SplitAfter(messageWithHeader, "\n")[1:], "\n")
+	message := strings.Join(strings.SplitAfter(messageWithHeader, "\n")[1:], "")
 	return strings.TrimSpace(message), err
 }
 

pkg/commands/git_commands/commit_test.go

@@ -161,3 +161,49 @@ func TestCommitShowCmdObj(t *testing.T) {
 		})
 	}
 }
+
+func TestGetCommitMsg(t *testing.T) {
+	type scenario struct {
+		testName       string
+		input          string
+		expectedOutput string
+	}
+	scenarios := []scenario{
+		{
+			"empty",
+			` commit deadbeef`,
+			``,
+		},
+		{
+			"no line breaks (single line)",
+			`commit deadbeef
+use generics to DRY up context code`,
+			`use generics to DRY up context code`,
+		},
+		{
+			"with line breaks",
+			`commit deadbeef
+Merge pull request #1750 from mark2185/fix-issue-template
+
+'git-rev parse' should be 'git rev-parse'`,
+			`Merge pull request #1750 from mark2185/fix-issue-template
+
+'git-rev parse' should be 'git rev-parse'`,
+		},
+	}
+
+	for _, s := range scenarios {
+		s := s
+		t.Run(s.testName, func(t *testing.T) {
+			instance := buildCommitCommands(commonDeps{
+				runner: oscommands.NewFakeRunner(t).Expect("git rev-list --format=%B --max-count=1 deadbeef", s.input, nil),
+			})
+
+			output, err := instance.GetCommitMessage("deadbeef")
+
+			assert.NoError(t, err)
+
+			assert.Equal(t, s.expectedOutput, output)
+		})
+	}
+}