Fix MemMapFs inconsistent path store

Adds a test that fails for the current MemMapFs when creating files in
nested directories with synonyms for the path (i.e. full path, relative
path, explict relative path).

Also fixes MemMapFs so that test (and all others pass).

memmap.go

@@ -177,9 +177,13 @@ func normalizePath(path string) string {
 		return FilePathSeparator
 	case "..":
 		return FilePathSeparator
-	default:
-		return path
 	}
+
+	// If path isn't rooted make it rooted
+	if !strings.HasPrefix(path, FilePathSeparator) {
+		path = FilePathSeparator + path
+	}
+	return path
 }
 
 func (m *MemMapFs) Open(name string) (File, error) {
@@ -351,6 +355,7 @@ func (m *MemMapFs) Stat(name string) (os.FileInfo, error) {
 
 func (m *MemMapFs) Chmod(name string, mode os.FileMode) error {
 	mode &= chmodBits
+	name = normalizePath(name)
 
 	m.mu.RLock()
 	f, ok := m.getData()[name]

memmap_test.go

@@ -833,3 +833,105 @@ func TestMemFsRenameDir(t *testing.T) {
 		t.Errorf("Cannot recreate the subdir in the source dir: %s", err)
 	}
 }
+
+func TestMemFsMkDir(t *testing.T) {
+	t.Parallel()
+
+	fs := NewMemMapFs()
+
+	// Creating a folder at "dir" or "/dir" or "./dir" should create the 'dir' directory at root
+	err := fs.Mkdir("a", 0o777)
+	if err != nil {
+		t.Fatalf("MkDir failed: %s", err)
+	}
+
+	err = fs.Mkdir("/b", 0o777)
+	if err != nil {
+		t.Fatalf("MkDir failed: %s", err)
+	}
+
+	err = fs.Mkdir("./c", 0o777)
+	if err != nil {
+		t.Fatalf("MkDir failed: %s", err)
+	}
+
+	// Listing root should return all folders
+	files, err := ReadDir(fs, "/")
+	if err != nil {
+		t.Fatalf("ReadDir failed: %s", err)
+	}
+
+	if len(files) != 3 {
+		t.Fatalf("Expected 3 files, got %d", len(files))
+	}
+
+	var foundA, foundB, foundC bool
+	for _, file := range files {
+		if !file.IsDir() {
+			t.Fatalf("Expected to find a directory not a file: %s", file.Name())
+		}
+		if file.Name() == "a" {
+			foundA = true
+		} else if file.Name() == "b" {
+			foundB = true
+		} else if file.Name() == "c" {
+			foundC = true
+		}
+	}
+
+	if !foundA || !foundB || !foundC {
+		t.Fatalf("Expected to find all files, but didn't")
+	}
+}
+
+func TestMemFsCreateFileNested(t *testing.T) {
+	t.Parallel()
+
+	fs := NewMemMapFs()
+
+	err := fs.Mkdir("dir", 0o777)
+	if err != nil {
+		t.Fatalf("MkDir failed: %s", err)
+	}
+
+	// Creating a file at "dir/a.txt" or "/dir/a.txt" or "./dir/a.txt" should create in the dir directory
+	err = WriteFile(fs, "dir/a.txt", []byte("test"), 0o777)
+	if err != nil {
+		t.Fatalf("WriteFile failed: %s", err)
+	}
+
+	err = WriteFile(fs, "/dir/b.txt", []byte("test"), 0o777)
+	if err != nil {
+		t.Fatalf("WriteFile failed: %s", err)
+	}
+
+	err = WriteFile(fs, "./dir/c.txt", []byte("test"), 0o777)
+	if err != nil {
+		t.Fatalf("WriteFile failed: %s", err)
+	}
+
+	// Listing dir should return all the files
+	files, err := ReadDir(fs, "/dir")
+	if err != nil {
+		t.Fatalf("ReadDir failed: %s", err)
+	}
+
+	if len(files) != 3 {
+		t.Fatalf("Expected 3 files, got %d", len(files))
+	}
+
+	var foundA, foundB, foundC bool
+	for _, file := range files {
+		if file.Name() == "a.txt" {
+			foundA = true
+		} else if file.Name() == "b.txt" {
+			foundB = true
+		} else if file.Name() == "c.txt" {
+			foundC = true
+		}
+	}
+
+	if !foundA || !foundB || !foundC {
+		t.Fatalf("Expected to find all files, but didn't")
+	}
+}