Fix version labeling in monorepos by adding --first-parent to git log

Ito-Ryu · Ito-Ryu · commit efef9f5d7ea2 · 2026-04-06T15:09:14.000+09:00
In monorepo setups using path filtering (tagPrefix), git log --merges
would hide merge commits due to "History Simplification" if the merge
result was TREESAME to the second parent.

Adding --first-parent ensures that merge commits on the release branch
that affect the specified path are correctly captured, allowing tagpr
to identify PR labels (major, minor, etc.) for correct versioning.
diff --git a/tagpr.go b/tagpr.go
@@ -405,7 +405,7 @@ func (tp *tagpr) Run(ctx context.Context) error {
 		tp.setOutput("pull_request", string(b))
 		return nil
 	}
-	mergeLogArgs := []string{"log", "--merges", "--pretty=format:%P",
+	mergeLogArgs := []string{"log", "--merges", "--first-parent", "--pretty=format:%P",
 		fmt.Sprintf("%s..%s/%s", fromCommitish, tp.remoteName, releaseBranch)}
 	if tp.normalizedTagPrefix != "" {
 		mergeLogArgs = append(mergeLogArgs, "--", strings.TrimSuffix(tp.normalizedTagPrefix, "/"))
diff --git a/tagpr_test.go b/tagpr_test.go
@@ -472,9 +472,9 @@ func TestBuildGitLogArgsWithPathFilter(t *testing.T) {
 		},
 		{
 			name:                "merge log with prefix",
-			baseArgs:            []string{"log", "--merges", "--pretty=format:%P", "v1.0.0..origin/main"},
+			baseArgs:            []string{"log", "--merges", "--first-parent", "--pretty=format:%P", "v1.0.0..origin/main"},
 			normalizedTagPrefix: "packages/core/",
-			wantArgs:            []string{"log", "--merges", "--pretty=format:%P", "v1.0.0..origin/main", "--", "packages/core"},
+			wantArgs:            []string{"log", "--merges", "--first-parent", "--pretty=format:%P", "v1.0.0..origin/main", "--", "packages/core"},
 		},
 		{
 			name:                "cherry-pick log with prefix",

Original file line number	Diff line number	Diff line change
`@@ -405,7 +405,7 @@ func (tp *tagpr) Run(ctx context.Context) error {`
`405`	`405`	`tp.setOutput("pull_request", string(b))`
`406`	`406`	`return nil`
`407`	`407`	`}`
`408`		`- mergeLogArgs := []string{"log", "--merges", "--pretty=format:%P",`
	`408`	`+ mergeLogArgs := []string{"log", "--merges", "--first-parent", "--pretty=format:%P",`
`409`	`409`	`fmt.Sprintf("%s..%s/%s", fromCommitish, tp.remoteName, releaseBranch)}`
`410`	`410`	`if tp.normalizedTagPrefix != "" {`
`411`	`411`	`mergeLogArgs = append(mergeLogArgs, "--", strings.TrimSuffix(tp.normalizedTagPrefix, "/"))`
Original file line number	Diff line number	Diff line change
`@@ -472,9 +472,9 @@ func TestBuildGitLogArgsWithPathFilter(t *testing.T) {`
`472`	`472`	`},`
`473`	`473`	`{`
`474`	`474`	`name: "merge log with prefix",`
`475`		`- baseArgs: []string{"log", "--merges", "--pretty=format:%P", "v1.0.0..origin/main"},`
	`475`	`+ baseArgs: []string{"log", "--merges", "--first-parent", "--pretty=format:%P", "v1.0.0..origin/main"},`
`476`	`476`	`normalizedTagPrefix: "packages/core/",`
`477`		`- wantArgs: []string{"log", "--merges", "--pretty=format:%P", "v1.0.0..origin/main", "--", "packages/core"},`
	`477`	`+ wantArgs: []string{"log", "--merges", "--first-parent", "--pretty=format:%P", "v1.0.0..origin/main", "--", "packages/core"},`
`478`	`478`	`},`
`479`	`479`	`{`
`480`	`480`	`name: "cherry-pick log with prefix",`