fix(dirty-set): correct lockfile detection in the fallback trigger

pkg/dirty_set.go

@@ -301,14 +301,49 @@ func propagateFrom(dirtyLabels, actuallyChanged map[string]bool, edges map[strin
 	return result
 }
 
+// nonLockfileExtensions are extensions a dependency lockfile never uses.
+// Lockfile detection matches on name fragments, so without this a script,
+// document or migration merely named after a lock forces a full rehash.
+//
+// Keep this list to executable code, images and prose. Anything that could
+// hold structured dependency data must stay off it, however unlikely it
+// looks: pip writes requirements_lock.txt, so ".txt" belongs to lockfiles,
+// and ".xml" is omitted for the same reason. Wrongly listing an extension
+// here silently under-reports impacted targets, which is far worse than the
+// redundant rehash a missing entry causes.
+var nonLockfileExtensions = map[string]bool{
+	".md": true, ".rst": true, ".html": true,
+	".png": true, ".jpg": true, ".jpeg": true, ".svg": true,
+	".sh": true, ".bash": true,
+	".go": true, ".java": true, ".py": true, ".ts": true, ".js": true,
+	".sql": true,
+}
+
+// looksLikeLockfile reports whether lowerBasename, already lowercased, names a
+// dependency lockfile. Three shapes occur: a ".lock" extension (Cargo.lock,
+// buf.lock), ".lock" as an inner component (multitool.lock.json,
+// .terraform.lock.hcl), and a "-lock" or "_lock" name stem (pnpm-lock.yaml,
+// package-lock.json). Only the first is unambiguous; the other two also match
+// ordinary files that happen to be named after a lock, so they additionally
+// require an extension a lockfile could plausibly use.
+func looksLikeLockfile(lowerBasename string) bool {
+	if strings.HasSuffix(lowerBasename, ".lock") {
+		return true
+	}
+	if !strings.Contains(lowerBasename, ".lock.") &&
+		!strings.Contains(lowerBasename, "-lock.") &&
+		!strings.Contains(lowerBasename, "_lock.") {
+		return false
+	}
+	return !nonLockfileExtensions[filepath.Ext(lowerBasename)]
+}
+
 func isFallbackTrigger(basename string) bool {
 	if strings.HasSuffix(basename, ".bzl") {
 		return true
 	}
 	lowerBasename := strings.ToLower(basename)
-	if strings.HasSuffix(lowerBasename, ".lock") ||
-		strings.Contains(lowerBasename, "-lock.") ||
-		strings.Contains(lowerBasename, "_lock.") {
+	if looksLikeLockfile(lowerBasename) {
 		return true
 	}
 	if basename == ".bazelrc" || strings.HasPrefix(basename, ".bazelrc.") ||

pkg/dirty_set_test.go

@@ -724,3 +724,82 @@ func TestPruneDirtySetReadsDependencyHashes(t *testing.T) {
 		t.Error("//app:consumer should be pruned: //pkg:tool is unchanged per DependencyHashes")
 	}
 }
+
+func TestIsFallbackTriggerLockfiles(t *testing.T) {
+	tests := []struct {
+		basename string
+		want     bool
+	}{
+		// Plain ".lock" extension.
+		{"Cargo.lock", true},
+		{"yarn.lock", true},
+		{"poetry.lock", true},
+		{"uv.lock", true},
+		{"buf.lock", true},
+		{"MODULE.bazel.lock", true},
+
+		// ".lock" as an inner component.
+		{"multitool.lock.json", true},
+		{".terraform.lock.hcl", true},
+
+		// "-lock" or "_lock" name stem.
+		{"pnpm-lock.yaml", true},
+		{"package-lock.json", true},
+		{"requirements_lock.txt", true},
+
+		// Extensions that could hold dependency data stay conservative, as
+		// does an unrecognised one.
+		{"deps-lock.xml", true},
+		{"deps-lock.xyz", true},
+
+		// Ordinary files merely named after a lock must not trigger.
+		{"merge-pnpm-lock.sh", false},
+		{"regen-pnpm-lock.sh", false},
+		{"repin-with-lock.sh", false},
+		{"2x-lock.png", false},
+		{"02_add_and_lock.md", false},
+		{"v3__workflow_lock.sql", false},
+
+		// Nothing lock-like at all.
+		{"README.md", false},
+		{"Main.java", false},
+	}
+
+	for _, tt := range tests {
+		if got := isFallbackTrigger(tt.basename); got != tt.want {
+			t.Errorf("isFallbackTrigger(%q) = %v, want %v", tt.basename, got, tt.want)
+		}
+	}
+}
+
+func TestComputeDirtySetNestedLockExtensionFallsBack(t *testing.T) {
+	changedFiles := map[string]string{
+		"tools/multitool.lock.json": "M",
+	}
+
+	result := ComputeDirtySet(changedFiles, nil, nil, nil)
+
+	if !result.NeedsFallback {
+		t.Fatal("expected fallback for multitool.lock.json change")
+	}
+	if result.FallbackCode != "unsafe_file_change" {
+		t.Errorf("FallbackCode = %q, want unsafe_file_change", result.FallbackCode)
+	}
+}
+
+func TestComputeDirtySetLockNamedScriptDoesNotFallBack(t *testing.T) {
+	edges := map[string][]string{
+		"//pkg:rule_a": {},
+	}
+	allLabels := CollectAllLabels(edges, nil)
+
+	changedFiles := map[string]string{
+		"tools/git/merge-pnpm-lock.sh": "M",
+	}
+
+	result := ComputeDirtySet(changedFiles, edges, allLabels, nil)
+
+	if result.NeedsFallback {
+		t.Errorf("unexpected fallback for a shell script: %s", result.FallbackReason)
+	}
+}