fix: handle multi-line commit message (#2244)

Fixes #2234

Author: JoeWang1127

internal/conventionalcommits/conventional_commits.go

@@ -190,17 +190,25 @@ func parseSimpleCommit(commitPart commitPart, commit *gitrepo.Commit, libraryID
 	processFooters(footers)
 
 	var commits []*ConventionalCommit
-	// If the body lines have multiple headers, separate them into  different conventional
-	// commit, all associated with the same commit sha.
-	// Note that we assume single line headers, the 2nd line of headers, if exists,
-	// will be discarded.
+	// Hold the subjects of each commit.
+	var subjects [][]string
+	// If the body lines have multiple headers, separate them into different conventional commit, all associated with
+	// the same commit sha.
 	for _, bodyLine := range bodyLines {
 		header, ok := parseHeader(bodyLine)
 		if !ok {
 			slog.Warn("bodyLine is not a header", "bodyLine", bodyLine, "hash", commit.Hash.String())
+			if len(commits) == 0 {
+				// This should not happen as we expect a conventional commit message inside a nested commit.
+				continue
+			}
+
+			// This might be a multi-line header, append the line to the subject of the last commit.
+			subjects[len(subjects)-1] = append(subjects[len(subjects)-1], strings.TrimSpace(bodyLine))
 			continue
 		}
 
+		subjects = append(subjects, []string{})
 		commits = append(commits, &ConventionalCommit{
 			Type:       header.Type,
 			Scope:      header.Scope,
@@ -214,10 +222,17 @@ func parseSimpleCommit(commitPart commitPart, commit *gitrepo.Commit, libraryID
 		})
 	}
 
-	// If only one conventional commit is found, i.e., only one header line is
-	// in the commit message, assign the body field.
 	if len(commits) == 1 {
+		// If only one conventional commit is found, i.e., only one header line is
+		// in the commit message, assign the body field.
 		commits[0].Body = strings.TrimSpace(strings.Join(bodyLines[1:], "\n"))
+	} else {
+		// Otherwise, concatenate all lines as the subject of the corresponding commit.
+		// This is a workaround when GitHub inserts line breaks in the middle of a long line after squash and merge.
+		for i, commit := range commits {
+			sub := fmt.Sprintf("%s %s", commit.Subject, strings.Join(subjects[i], " "))
+			commit.Subject = strings.TrimSpace(sub)
+		}
 	}
 
 	return commits, nil

internal/conventionalcommits/conventional_commits_test.go

@@ -393,7 +393,7 @@ END_NESTED_COMMIT`,
 			},
 		},
 		{
-			name: "parse multiple lines message inside nested commit",
+			name: "parse multiple lines message inside nested commit, one line header",
 			message: `
 chore: Update generation configuration at Tue Aug 26 02:31:23 UTC 2025 (#11734)
 
@@ -453,6 +453,57 @@ END_COMMIT_OVERRIDE`,
 				},
 			},
 		},
+		{
+			name: "parse_multiple_lines_message_inside_nested_commit_multi_line_headers",
+			message: `
+chore: Update generation configuration at Tue Aug 26 02:31:23 UTC 2025 (#11734)
+
+This pull request is generated with proto changes between
+[googleapis/googleapis@525c95a](https://github.com/googleapis/googleapis/commit/525c95a7a122ec2869ae06cd02fa5013819463f6)
+(exclusive) and
+[googleapis/googleapis@b738e78](https://github.com/googleapis/googleapis/commit/b738e78ed63effb7d199ed2d61c9e03291b6077f)
+(inclusive).
+
+BEGIN_COMMIT_OVERRIDE
+BEGIN_NESTED_COMMIT
+feat: [texttospeech] Support promptable voices by specifying a model
+name and a prompt
+feat: [texttospeech] Add enum value M4A to enum AudioEncoding
+docs: [texttospeech] A comment for method 'StreamingSynthesize' in
+service 'TextToSpeech' is changed
+
+END_NESTED_COMMIT
+END_COMMIT_OVERRIDE`,
+			want: []*ConventionalCommit{
+				{
+					Type:      "feat",
+					Subject:   "[texttospeech] Support promptable voices by specifying a model name and a prompt",
+					LibraryID: "example-id",
+					IsNested:  true,
+					Footers:   map[string]string{},
+					SHA:       sha.String(),
+					When:      now,
+				},
+				{
+					Type:      "feat",
+					Subject:   "[texttospeech] Add enum value M4A to enum AudioEncoding",
+					LibraryID: "example-id",
+					IsNested:  true,
+					Footers:   map[string]string{},
+					SHA:       sha.String(),
+					When:      now,
+				},
+				{
+					Type:      "docs",
+					Subject:   "[texttospeech] A comment for method 'StreamingSynthesize' in service 'TextToSpeech' is changed",
+					LibraryID: "example-id",
+					IsNested:  true,
+					Footers:   map[string]string{},
+					SHA:       sha.String(),
+					When:      now,
+				},
+			},
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			commit := &gitrepo.Commit{

internal/librarian/release_notes.go

@@ -208,7 +208,7 @@ func formatGenerationPRBody(repo gitrepo.Repository, state *config.LibrarianStat
 
 // findLatestGenerationCommit returns the latest commit among the last generated
 // commit of all the libraries.
-// A libray is skipped if the last generated commit is empty.
+// A library is skipped if the last generated commit is empty.
 //
 // Note that it is possible that the returned commit is nil.
 func findLatestGenerationCommit(repo gitrepo.Repository, state *config.LibrarianState, idToCommits map[string]string) (*gitrepo.Commit, error) {