From 524503031c0a9f3d2c77a6d5db8b875b54f1f5dc Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Wed, 1 Apr 2026 22:59:18 -0700
Subject: [PATCH] [ILibrary / LazyLibrary] allow mapping a name to itself

---
 masque/library.py           | 12 ++++++++++++
 masque/test/test_library.py | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/masque/library.py b/masque/library.py
index 5a60e8d..d7a30af 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -828,6 +828,9 @@ class ILibrary(ILibraryView, MutableMapping[str, 'Pattern'], metaclass=ABCMeta):
         """
         if old_name not in self:
             raise LibraryError(f'"{old_name}" does not exist in the library.')
+        if old_name == new_name:
+            return self
+
         self[new_name] = self[old_name]
         del self[old_name]
         if move_references:
@@ -852,6 +855,9 @@ class ILibrary(ILibraryView, MutableMapping[str, 'Pattern'], metaclass=ABCMeta):
         Returns:
             self
         """
+        if old_target == new_target:
+            return self
+
         for pattern in self.values():
             if old_target in pattern.refs:
                 pattern.refs[new_target].extend(pattern.refs[old_target])
@@ -1483,6 +1489,9 @@ class LazyLibrary(ILibrary):
         """
         if old_name not in self.mapping:
             raise LibraryError(f'"{old_name}" does not exist in the library.')
+        if old_name == new_name:
+            return self
+
         self[new_name] = self.mapping[old_name]        # copy over function
         if old_name in self.cache:
             self.cache[new_name] = self.cache[old_name]
@@ -1504,6 +1513,9 @@ class LazyLibrary(ILibrary):
         Returns:
             self
         """
+        if old_target == new_target:
+            return self
+
         self.precache()
         for pattern in self.cache.values():
             if old_target in pattern.refs:
diff --git a/masque/test/test_library.py b/masque/test/test_library.py
index 621e703..ce564aa 100644
--- a/masque/test/test_library.py
+++ b/masque/test/test_library.py
@@ -221,6 +221,28 @@ def test_library_rename() -> None:
     assert "old" not in lib["parent"].refs
 
 
+@pytest.mark.parametrize("library_cls", (Library, LazyLibrary))
+def test_library_rename_self_is_noop(library_cls: type[Library] | type[LazyLibrary]) -> None:
+    lib = library_cls()
+    lib["top"] = Pattern()
+    lib["parent"] = Pattern()
+    lib["parent"].ref("top")
+
+    lib.rename("top", "top", move_references=True)
+
+    assert set(lib.keys()) == {"top", "parent"}
+    assert "top" in lib["parent"].refs
+    assert len(lib["parent"].refs["top"]) == 1
+
+
+@pytest.mark.parametrize("library_cls", (Library, LazyLibrary))
+def test_library_rename_top_self_is_noop(library_cls: type[Library] | type[LazyLibrary]) -> None:
+    lib = library_cls()
+    lib["top"] = Pattern()
+
+    lib.rename_top("top")
+
+    assert list(lib.keys()) == ["top"]
 
 
 @pytest.mark.parametrize("library_cls", (Library, LazyLibrary))
@@ -230,6 +252,21 @@ def test_library_rename_missing_raises_library_error(library_cls: type[Library]
 
     with pytest.raises(LibraryError, match="does not exist"):
         lib.rename("missing", "new")
+
+
+@pytest.mark.parametrize("library_cls", (Library, LazyLibrary))
+def test_library_move_references_same_target_is_noop(library_cls: type[Library] | type[LazyLibrary]) -> None:
+    lib = library_cls()
+    lib["top"] = Pattern()
+    lib["parent"] = Pattern()
+    lib["parent"].ref("top")
+
+    lib.move_references("top", "top")
+
+    assert "top" in lib["parent"].refs
+    assert len(lib["parent"].refs["top"]) == 1
+
+
 def test_library_dfs_can_replace_existing_patterns() -> None:
     lib = Library()
     child = Pattern()