Add pass to removed blocks of code (#386)

.gitignore

@@ -2,7 +2,7 @@
 .pydevproject
 .idea
 .tox
-.coverage
+.coverage*
 .cache
 .eggs/
 *.egg-info/

docs/versionhistory.rst

@@ -6,11 +6,14 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 **UNRELEASED**
 
 - Dropped Python 3.7 support
+- Fixed ``@typechecked`` optimization causing compilation of instrumented code to fail
+  when any block was left empty by the AST transformer (eg `if` or `try` / `except` blocks)
+  (`#352 <https://github.com/agronholm/typeguard/issues/352>`_)
 
 **4.1.2** (2023-08-18)
 
 - Fixed ``Any`` being removed from a subscript that still contains other elements
-  (`#373 <https://github.com/agronholm/typeguard/issues/373>`_
+  (`#373 <https://github.com/agronholm/typeguard/issues/373>`_)
 
 **4.1.1** (2023-08-16)
 
@@ -21,7 +24,7 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 
 - Added support for passing a tuple as ``expected_type`` to ``check_type()``, making it
   more of a drop-in replacement for ``isinstance()``
-  (`#371 <https://github.com/agronholm/typeguard/issues/371>`_
+  (`#371 <https://github.com/agronholm/typeguard/issues/371>`_)
 - Fixed regression where ``Literal`` inside a ``Union`` had quotes stripped from its
   contents, thus typically causing ``NameError`` to be raised when run
   (`#372 <https://github.com/agronholm/typeguard/issues/372>`_)

src/typeguard/_transformer.py

@@ -55,6 +55,7 @@
     copy_location,
     expr,
     fix_missing_locations,
+    iter_fields,
     keyword,
     walk,
 )
@@ -498,6 +499,21 @@ def __init__(
         self.target_node: FunctionDef | AsyncFunctionDef | None = None
         self.target_lineno = target_lineno
 
+    def generic_visit(self, node: AST) -> AST:
+        non_empty_list_fields = []
+        for field_name, val in iter_fields(node):
+            if isinstance(val, list) and len(val) > 0:
+                non_empty_list_fields.append(field_name)
+
+        node = super().generic_visit(node)
+
+        # Add `pass` to list fields that were optimised away
+        for field_name in non_empty_list_fields:
+            if not getattr(node, field_name, None):
+                setattr(node, field_name, [Pass()])
+
+        return node
+
     @contextmanager
     def _use_memo(
         self, node: ClassDef | FunctionDef | AsyncFunctionDef
@@ -1175,11 +1191,6 @@ def visit_If(self, node: If) -> Any:
         """
         self.generic_visit(node)
 
-        # Fix empty node body (caused by removal of classes/functions not on the target
-        # path)
-        if not node.body:
-            node.body.append(Pass())
-
         if (
             self._memo is self._module_memo
             and isinstance(node.test, Name)

tests/test_transformer.py

@@ -1523,6 +1523,53 @@ def foo(x: str) -> None:
     )
 
 
+def test_dont_leave_empty_ast_container_nodes_2() -> None:
+    # Regression test for #352
+    node = parse(
+        dedent(
+            """
+            try:
+
+                class A:
+                    ...
+
+                def func():
+                    ...
+
+            except:
+
+                class A:
+                    ...
+
+                def func():
+                    ...
+
+
+            def foo(x: str) -> None:
+                pass
+            """
+        )
+    )
+    TypeguardTransformer(["foo"]).visit(node)
+    assert (
+        unparse(node)
+        == dedent(
+            """
+            try:
+                pass
+            except:
+                pass
+
+            def foo(x: str) -> None:
+                from typeguard import TypeCheckMemo
+                from typeguard._functions import check_argument_types
+                memo = TypeCheckMemo(globals(), locals())
+                check_argument_types('foo', {'x': (x, str)}, memo)
+            """
+        ).strip()
+    )
+
+
 def test_dont_parse_annotated_2nd_arg() -> None:
     # Regression test for #352
     node = parse(