Insert co_return if coroutine has no return statement

trans/transpiler/phases/emit_cpp/block.py

@@ -4,7 +4,7 @@ from dataclasses import dataclass
 from typing import Iterable, Optional
 
 from transpiler.phases.typing.scope import Scope
-from transpiler.phases.typing.types import BaseType, TY_INT, TY_BOOL, TypeVariable
+from transpiler.phases.typing.types import BaseType, TY_INT, TY_BOOL, TypeVariable, Promise
 from transpiler.utils import compare_ast
 from transpiler.phases.emit_cpp import NodeVisitor, CoroutineMode, flatmap
 from transpiler.phases.emit_cpp.expr import ExpressionVisitor
@@ -103,6 +103,21 @@ class BlockVisitor(NodeVisitor):
 
         yield "{"
 
+        class ReturnVisitor(SearchVisitor):
+            def visit_Return(self, node: ast.Return) -> bool:
+                yield True
+
+            def visit_Yield(self, node: ast.Yield) -> bool:
+                yield True
+
+            def visit_FunctionDef(self, node: ast.FunctionDef):
+                yield from ()
+
+            def visit_ClassDef(self, node: ast.ClassDef):
+                yield from ()
+
+        has_return = ReturnVisitor().match(node.body)
+
         for child in node.body:
             from transpiler.phases.emit_cpp.function import FunctionVisitor
             child_visitor = FunctionVisitor(inner_scope, CoroutineMode.ASYNC)
@@ -113,6 +128,9 @@ class BlockVisitor(NodeVisitor):
                 yield f" {name};"
             yield from child_visitor.visit(child)
 
+        if not has_return and isinstance(node.type.return_type, Promise):
+            yield "co_return;"
+
         yield "}"