fix: do not delete any files in .librarian/generator-input directory (#1934)

In case the remove-regex contains a directory that exists in
.librarian/generator-input, the librarian CLI should not delete it when
calling clean.

fixes: #1925

Author: ldetmer

internal/librarian/command.go

@@ -41,6 +41,10 @@ const (
 	release  = "release"
 )
 
+var globalPreservePatterns = []string{
+	fmt.Sprintf(`^%s(/.*)?$`, regexp.QuoteMeta(config.GeneratorInputDir)), // Preserve the generator-input directory and its contents.
+}
+
 // GitHubClientFactory type for creating a GitHubClient.
 type GitHubClientFactory func(token string, repo *github.Repository) (GitHubClient, error)
 
@@ -254,7 +258,10 @@ func cleanAndCopyLibrary(state *config.LibrarianState, repoDir, libraryID, outpu
 		}
 	}
 
-	if err := clean(repoDir, removePatterns, library.PreserveRegex); err != nil {
+	preservePatterns := append(library.PreserveRegex,
+		globalPreservePatterns...)
+
+	if err := clean(repoDir, removePatterns, preservePatterns); err != nil {
 		return fmt.Errorf("failed to clean library, %s: %w", library.ID, err)
 	}
 

internal/librarian/command_test.go

@@ -388,6 +388,111 @@ func TestCleanAndCopyLibrary(t *testing.T) {
 				"a/path/stale.txt",
 			},
 		},
+		{
+			name:      "clean never deletes generator-input directory",
+			libraryID: "some-library",
+			state: &config.LibrarianState{
+				Libraries: []*config.LibraryState{
+					{
+						ID:          "some-library",
+						SourceRoots: []string{"a/path"},
+						RemoveRegex: []string{"a/path"},
+					},
+				},
+			},
+			repo: newTestGitRepo(t),
+			setup: func(t *testing.T, repoDir, outputDir string) {
+				// Create a file in the repo directory to test cleaning.
+				fileToBeDeleted := filepath.Join(repoDir, "a/path/delete.txt")
+				fileToNotBeDeleted := filepath.Join(repoDir, ".librarian/generator-input/a/path/do-not-delete.txt")
+				if err := os.MkdirAll(filepath.Dir(fileToBeDeleted), 0755); err != nil {
+					t.Fatal(err)
+				}
+				if _, err := os.Create(fileToBeDeleted); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.MkdirAll(filepath.Dir(fileToNotBeDeleted), 0755); err != nil {
+					t.Fatal(err)
+				}
+				if _, err := os.Create(fileToNotBeDeleted); err != nil {
+					t.Fatal(err)
+				}
+
+				// Create generated files in the output directory.
+				filesToCreate := []string{
+					"a/path/new_generated_file_to_copy.txt",
+				}
+				for _, relPath := range filesToCreate {
+					fullPath := filepath.Join(outputDir, relPath)
+					if err := os.MkdirAll(filepath.Dir(fullPath), 0755); err != nil {
+						t.Fatal(err)
+					}
+					if _, err := os.Create(fullPath); err != nil {
+						t.Fatal(err)
+					}
+				}
+			},
+			shouldCopy: []string{
+				".librarian/generator-input/a/path/do-not-delete.txt",
+				"a/path/new_generated_file_to_copy.txt",
+			},
+			shouldDelete: []string{
+				"a/path/delete.txt",
+			},
+		},
+		{
+			name:      "if same value is present in preserve regex and global preserver regex list there is no conflict",
+			libraryID: "some-library",
+			state: &config.LibrarianState{
+				Libraries: []*config.LibraryState{
+					{
+						ID:            "some-library",
+						SourceRoots:   []string{"a/path"},
+						RemoveRegex:   []string{"a/path"},
+						PreserveRegex: globalPreservePatterns,
+					},
+				},
+			},
+			repo: newTestGitRepo(t),
+			setup: func(t *testing.T, repoDir, outputDir string) {
+				// Create a file in the repo directory to test cleaning.
+				fileToBeDeleted := filepath.Join(repoDir, "a/path/delete.txt")
+				fileToNotBeDeleted := filepath.Join(repoDir, ".librarian/generator-input/a/path/do-not-delete.txt")
+				if err := os.MkdirAll(filepath.Dir(fileToBeDeleted), 0755); err != nil {
+					t.Fatal(err)
+				}
+				if _, err := os.Create(fileToBeDeleted); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.MkdirAll(filepath.Dir(fileToNotBeDeleted), 0755); err != nil {
+					t.Fatal(err)
+				}
+				if _, err := os.Create(fileToNotBeDeleted); err != nil {
+					t.Fatal(err)
+				}
+
+				// Create generated files in the output directory.
+				filesToCreate := []string{
+					"a/path/new_generated_file_to_copy.txt",
+				}
+				for _, relPath := range filesToCreate {
+					fullPath := filepath.Join(outputDir, relPath)
+					if err := os.MkdirAll(filepath.Dir(fullPath), 0755); err != nil {
+						t.Fatal(err)
+					}
+					if _, err := os.Create(fullPath); err != nil {
+						t.Fatal(err)
+					}
+				}
+			},
+			shouldCopy: []string{
+				".librarian/generator-input/a/path/do-not-delete.txt",
+				"a/path/new_generated_file_to_copy.txt",
+			},
+			shouldDelete: []string{
+				"a/path/delete.txt",
+			},
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			repoDir := test.repo.GetDir()