fix: use empty line as a title-body separator (#2345)

GitHub will insert an empty line between commit title and body, we use
this as an indicator of separating title and message.

Line breaks are not reliable because GitHub will wrap long lines with
line breaks during squash and merge.

Created release pull request:
#2346

Fixes #2234

Author: JoeWang1127

internal/conventionalcommits/conventional_commits.go

@@ -210,6 +210,10 @@ func parseSimpleCommit(commitPart commitPart, commit *gitrepo.Commit, libraryID
 	var commits []*ConventionalCommit
 	// Hold the subjects of each commit.
 	var subjects [][]string
+	// Hold the body of each commit.
+	var body [][]string
+	// Whether it has seen an empty line.
+	var foundSeparator bool
 	// If the body lines have multiple headers, separate them into different conventional commit, all associated with
 	// the same commit sha.
 	for _, bodyLine := range bodyLines {
@@ -221,12 +225,26 @@ func parseSimpleCommit(commitPart commitPart, commit *gitrepo.Commit, libraryID
 				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))
+			bodyLine = strings.TrimSpace(bodyLine)
+			if bodyLine == "" {
+				foundSeparator = true
+				continue
+			}
+
+			if foundSeparator {
+				// Since we have seen a separator, the rest of the lines are body lines of the commit.
+				body[len(body)-1] = append(body[len(body)-1], bodyLine)
+			} else {
+				// We haven't seen a separator, this line is the continuation of the title.
+				subjects[len(subjects)-1] = append(subjects[len(subjects)-1], bodyLine)
+			}
+
 			continue
 		}
 
 		subjects = append(subjects, []string{})
+		body = append(body, []string{})
+		foundSeparator = false
 		// If there is an association for the commit (i.e. the commit has '[LIBRARY_ID]' in the
 		// description), then use that libraryID. Otherwise, use the libraryID passed as the default.
 		headerLibraryID := header.extractLibraryID()
@@ -248,17 +266,10 @@ func parseSimpleCommit(commitPart commitPart, commit *gitrepo.Commit, libraryID
 		})
 	}
 
-	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)
-		}
+	for i, commit := range commits {
+		sub := fmt.Sprintf("%s %s", commit.Subject, strings.Join(subjects[i], " "))
+		commit.Subject = strings.TrimSpace(sub)
+		commit.Body = strings.Join(body[i], "\n")
 	}
 
 	return commits, nil

internal/conventionalcommits/conventional_commits_test.go

@@ -121,7 +121,7 @@ func TestParseCommits(t *testing.T) {
 		},
 		{
 			name:    "commit_with_multiple_footers_for_generated_changes",
-			message: "feat: [library-name] add new feature\nThis is the body.\n...\n\nPiperOrigin-RevId: piper_cl_number\n\nSource-Link: [googleapis/googleapis@{source_commit_hash}](https://github.com/googleapis/googleapis/commit/abcdefg1234567)",
+			message: "feat: [library-name] add new feature\n\nThis is the body.\n...\n\nPiperOrigin-RevId: piper_cl_number\n\nSource-Link: [googleapis/googleapis@{source_commit_hash}](https://github.com/googleapis/googleapis/commit/abcdefg1234567)",
 			want: []*ConventionalCommit{
 				{
 					Type:       "feat",
@@ -250,8 +250,9 @@ END_COMMIT_OVERRIDE`,
 			wantErrPhrase: "empty commit",
 		},
 		{
-			name: "commit with nested commit",
+			name: "commit_with_nested_commit",
 			message: `feat(parser): main feature
+
 main commit body
 
 BEGIN_NESTED_COMMIT
@@ -305,7 +306,7 @@ END_NESTED_COMMIT
 		{
 			name: "commit_with_empty_nested_commit",
 			message: `feat(parser): main feature
-main commit body
+2nd line of title
 
 BEGIN_NESTED_COMMIT
 END_NESTED_COMMIT
@@ -314,8 +315,7 @@ END_NESTED_COMMIT
 				{
 					Type:       "feat",
 					Scope:      "parser",
-					Subject:    "main feature",
-					Body:       "main commit body",
+					Subject:    "main feature 2nd line of title",
 					LibraryID:  "example-id",
 					IsNested:   false,
 					Footers:    map[string]string{},
@@ -338,6 +338,7 @@ Language Image: {language_image_name_and_digest}
 BEGIN_COMMIT_OVERRIDE
 BEGIN_NESTED_COMMIT
 feat: [abc] nested commit 1
+
 body of nested commit 1
 ...
 
@@ -347,6 +348,7 @@ Source-Link: fake-link
 END_NESTED_COMMIT
 BEGIN_NESTED_COMMIT
 feat: [abc] nested commit 2
+
 body of nested commit 2
 ...
 

internal/librarian/release_notes.go

@@ -76,9 +76,9 @@ Language Image: {{.ImageVersion}}
 ### {{.Heading}}
 {{ range .Commits }}
 {{ if index .Footers "PiperOrigin-RevId" -}}
-* {{.Subject}} {{.Body}} (PiperOrigin-RevId: {{index .Footers "PiperOrigin-RevId"}}) ([{{shortSHA .CommitHash}}]({{"https://github.com/"}}{{$noteSection.RepoOwner}}/{{$noteSection.RepoName}}/commit/{{shortSHA .CommitHash}}))
+* {{.Subject}} (PiperOrigin-RevId: {{index .Footers "PiperOrigin-RevId"}}) ([{{shortSHA .CommitHash}}]({{"https://github.com/"}}{{$noteSection.RepoOwner}}/{{$noteSection.RepoName}}/commit/{{shortSHA .CommitHash}}))
 {{- else -}}
-* {{.Subject}} {{.Body}} ([{{shortSHA .CommitHash}}]({{"https://github.com/"}}{{$noteSection.RepoOwner}}/{{$noteSection.RepoName}}/commit/{{shortSHA .CommitHash}}))
+* {{.Subject}} ([{{shortSHA .CommitHash}}]({{"https://github.com/"}}{{$noteSection.RepoOwner}}/{{$noteSection.RepoName}}/commit/{{shortSHA .CommitHash}}))
 {{- end }}
 {{ end }}
 

internal/librarian/release_notes_test.go

@@ -529,11 +529,11 @@ Language Image: go:1.21
 
 ### Features
 
-* new feature  ([1234567](https://github.com/owner/repo/commit/1234567))
+* new feature ([1234567](https://github.com/owner/repo/commit/1234567))
 
 ### Bug Fixes
 
-* a bug fix  ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
+* a bug fix ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
 
 </details>`,
 				librarianVersion, today),
@@ -579,17 +579,17 @@ Language Image: go:1.21
 
 ### Features
 
-* new feature  (PiperOrigin-RevId: 123456) ([1234567](https://github.com/owner/repo/commit/1234567))
+* new feature (PiperOrigin-RevId: 123456) ([1234567](https://github.com/owner/repo/commit/1234567))
 
 ### Bug Fixes
 
-* a bug fix  (PiperOrigin-RevId: 987654) ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
+* a bug fix (PiperOrigin-RevId: 987654) ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
 
 </details>`,
 				librarianVersion, today),
 		},
 		{
-			name: "single library with multiple features",
+			name: "single_library_with_multiple_features",
 			state: &config.LibrarianState{
 				Image: "go:1.21",
 				Libraries: []*config.LibraryState{
@@ -623,9 +623,9 @@ Language Image: go:1.21
 
 ### Features
 
-* new feature  ([1234567](https://github.com/owner/repo/commit/1234567))
+* new feature ([1234567](https://github.com/owner/repo/commit/1234567))
 
-* another new feature  ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
+* another new feature ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
 
 </details>`,
 				librarianVersion, today),
@@ -674,7 +674,7 @@ Language Image: go:1.21
 
 ### Features
 
-* feature for a  ([1234567](https://github.com/owner/repo/commit/1234567))
+* feature for a ([1234567](https://github.com/owner/repo/commit/1234567))
 
 </details>
 
@@ -685,7 +685,7 @@ Language Image: go:1.21
 
 ### Bug Fixes
 
-* fix for b  ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
+* fix for b ([fedcba0](https://github.com/owner/repo/commit/fedcba0))
 
 </details>`,
 				librarianVersion, today, today),
@@ -725,7 +725,7 @@ Language Image: go:1.21
 
 ### Features
 
-* new feature  ([1234567](https://github.com/owner/repo/commit/1234567))
+* new feature ([1234567](https://github.com/owner/repo/commit/1234567))
 
 </details>`,
 				librarianVersion, today),
@@ -761,7 +761,7 @@ Language Image: go:1.21
 
 ### Features
 
-* new feature this is the body ([1234567](https://github.com/owner/repo/commit/1234567))
+* new feature ([1234567](https://github.com/owner/repo/commit/1234567))
 
 </details>`,
 				librarianVersion, today),