fix: return an error instead of panicking on orphaned MemMapFs Remove

unRegisterWithParent called log.Panic when a file's parent directory was
no longer registered (for example when the parent was removed first),
crashing the whole program from an ordinary Remove call. Return a normal
error instead so Remove, RemoveAll and Rename can surface it to the
caller. The now-unused log import is dropped.

Fixes #388

memmap.go

@@ -16,7 +16,6 @@ package afero
 import (
 	"fmt"
 	"io"
-	"log"
 	"os"
 	"path/filepath"
 	"sort"
@@ -71,7 +70,11 @@ func (m *MemMapFs) unRegisterWithParent(fileName string) error {
 	}
 	parent := m.findParent(f)
 	if parent == nil {
-		log.Panic("parent of ", f.Name(), " is nil")
+		// The parent directory is no longer registered (for example it was
+		// removed before this file). There is nothing to unregister from, and
+		// crashing the whole process is never appropriate, so surface an error
+		// that callers can handle.
+		return fmt.Errorf("parent of %s is nil", f.Name())
 	}
 
 	parent.Lock()

memmap_test.go

@@ -135,6 +135,29 @@ func TestOpenFileExcl(t *testing.T) {
 	checkPathError(t, err, "Open")
 }
 
+// Regression test for #388: removing a file whose parent directory is no
+// longer registered must return an error instead of panicking. Previously
+// unRegisterWithParent called log.Panic, which crashed the whole process.
+func TestMemFsRemoveWithUnregisteredParent(t *testing.T) {
+	fs := NewMemMapFs()
+	if err := fs.MkdirAll("/foo/bar", 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := WriteFile(fs, "/foo/bar/baz.txt", []byte("data"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Drop the parent directory entry, leaving the file dangling.
+	if err := fs.Remove("/foo/bar"); err != nil {
+		t.Fatalf("removing parent dir failed: %v", err)
+	}
+
+	// Removing the now-orphaned file must not panic; it must return an error.
+	if err := fs.Remove("/foo/bar/baz.txt"); err == nil {
+		t.Fatalf("expected an error removing a file with an unregistered parent, got nil")
+	}
+}
+
 // Ensure Permissions are set on OpenFile/Mkdir/MkdirAll
 func TestPermSet(t *testing.T) {
 	const fileName = "/myFileTest"