fix: prevent pattern loader temporary directory leaks

- Create pattern temporary directories only during database population.
- Remove temporary directories after successful or failed downloads.
- Add regression tests for lazy creation and cleanup.
- Document pattern loader cleanup behavior in changelog.

cmd/generate_changelog/incoming/2211.txt

@@ -0,0 +1,4 @@
+### PR [#2211](https://github.com/danielmiessler/Fabric/pull/2211) by [ksylvan](https://github.com/ksylvan): fix: prevent pattern loader temporary directory leaks
+
+- Prevent pattern loader leaks by lazily creating temporary directories during database population and cleaning them up after successful or failed downloads.
+- Add regression tests for lazy directory creation and cleanup.

internal/tools/patterns_loader.go

@@ -59,13 +59,6 @@ type PatternsLoader struct {
 
 func (o *PatternsLoader) configure() (err error) {
 	o.pathPatternsPrefix = fmt.Sprintf("%v/", o.DefaultFolder.Value)
-	// Use a consistent temp folder name regardless of the source path structure
-	tempDir, err := os.MkdirTemp("", "fabric-patterns-")
-	if err != nil {
-		return fmt.Errorf(i18n.T("patterns_failed_create_temp_folder"), err)
-	}
-	o.tempPatternsFolder = tempDir
-
 	return
 }
 
@@ -96,6 +89,15 @@ func (o *PatternsLoader) PopulateDB() (err error) {
 	fmt.Println()
 	fmt.Println()
 
+	// Create the temp folder here, not in configure(), so invocations that
+	// do not download patterns do not leak an empty directory (issue #2190).
+	var tempDir string
+	if tempDir, err = os.MkdirTemp("", "fabric-patterns-"); err != nil {
+		return fmt.Errorf(i18n.T("patterns_failed_create_temp_folder"), err)
+	}
+	o.tempPatternsFolder = tempDir
+	defer os.RemoveAll(tempDir)
+
 	originalPath := o.DefaultFolder.Value
 	if err = o.gitCloneAndCopy(); err != nil {
 		return fmt.Errorf(i18n.T("patterns_failed_download_from_git"), err)

internal/tools/patterns_loader_test.go

@@ -0,0 +1,63 @@
+package tools
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/danielmiessler/fabric/internal/plugins/db/fsdb"
+)
+
+// Configure runs on every fabric invocation via the plugin registry. It must
+// not create the patterns temp directory; only PopulateDB uses it.
+func TestConfigureDoesNotCreateTempDir(t *testing.T) {
+	tmp := t.TempDir()
+	t.Setenv("TMPDIR", tmp)
+	t.Setenv("TMP", tmp)
+	t.Setenv("TEMP", tmp)
+
+	loader := NewPatternsLoader(&fsdb.PatternsEntity{
+		StorageEntity: &fsdb.StorageEntity{Dir: t.TempDir()},
+	})
+	if err := loader.Configure(); err != nil {
+		t.Fatalf("Configure() failed: %v", err)
+	}
+
+	matches, err := filepath.Glob(filepath.Join(tmp, "fabric-patterns-*"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(matches) != 0 {
+		t.Errorf("Configure() created temp directories: %v", matches)
+	}
+}
+
+// PopulateDB must create the temp directory lazily and remove it when done,
+// even on failure.
+func TestPopulateDBCleansUpTempDir(t *testing.T) {
+	tmp := t.TempDir()
+	t.Setenv("TMPDIR", tmp)
+	t.Setenv("TMP", tmp)
+	t.Setenv("TEMP", tmp)
+
+	loader := NewPatternsLoader(&fsdb.PatternsEntity{
+		StorageEntity: &fsdb.StorageEntity{Dir: t.TempDir()},
+	})
+	if err := loader.Configure(); err != nil {
+		t.Fatalf("Configure() failed: %v", err)
+	}
+	// Point at an invalid repo so PopulateDB fails fast without network.
+	loader.DefaultGitRepoUrl.Value = filepath.Join(t.TempDir(), "no-such-repo")
+
+	if err := loader.PopulateDB(); err == nil {
+		t.Fatal("PopulateDB() unexpectedly succeeded with invalid repo")
+	}
+
+	entries, err := os.ReadDir(tmp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, e := range entries {
+		t.Errorf("PopulateDB() left temp entry behind: %v", e.Name())
+	}
+}