[core] Call a lambda whose only statement returns a braced value (#19503)

esphome/cpp_generator.py

@@ -1212,7 +1212,13 @@ def call_lambda(lamb: LambdaExpression) -> Expression:
     assert lamb.return_type is not None, "Lambda must have a return type to be called"
     expr = lamb.content.strip()
     # A lone `return <expr>;` reduces to the expression; anything longer is called as is.
-    if re.match(r"^return\b", expr) and expr.endswith(";") and expr.count(";") == 1:
+    # A braced return such as `return {};` needs the lambda's return type, so it is called.
+    if (
+        re.match(r"^return\b", expr)
+        and expr.endswith(";")
+        and expr.count(";") == 1
+        and not expr[6:].lstrip().startswith("{")
+    ):
         expr = RawExpression(expr[6:-1].strip())
         # Don't cast if the return type is a class
         if isinstance(lamb.return_type, MockObjClass):

tests/unit_tests/test_cpp_generator.py

@@ -260,6 +260,15 @@ class TestCallLambda:
         assert isinstance(result, cg.CallExpression)
         assert str(result).endswith("}()")
 
+    def test_call_lambda__braced_return_is_called(self) -> None:
+        """A braced return needs the lambda's return type, so it is not reduced."""
+        lamb = cg.LambdaExpression(("return {};",), (), "", ct.int_)
+
+        result = cg.call_lambda(lamb)
+
+        assert isinstance(result, cg.CallExpression)
+        assert "static_cast" not in str(result)
+
     def test_call_lambda__return_expression_with_class_return_type_no_cast(self):
         """A class return type is not cast, since static_cast doesn't apply
         to arbitrary class types."""