Usability: Warning when user calls "return" from their autoqasm entry point function

src/braket/experimental/autoqasm/converters/return_statements.py

@@ -0,0 +1,40 @@
+# Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+#     http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+
+
+"""Converters for return statement nodes."""
+
+import ast
+import warnings
+
+from braket.experimental.autoqasm import program
+from braket.experimental.autoqasm.autograph.converters import return_statements
+from braket.experimental.autoqasm.autograph.core import ag_ctx, converter
+
+
+class ReturnValidator(converter.Base):
+    def visit_Return(self, node: ast.stmt) -> ast.stmt:
+        aq_context = program.get_program_conversion_context()
+        if not aq_context.subroutines_processing and node.value is not None:
+            warnings.warn("Return value from top level function is ignored.")
+        return node
+
+
+def transform(
+    node: ast.stmt, ctx: ag_ctx.ControlStatusCtx, default_to_null_return: bool = True
+) -> ast.stmt:
+    """Handle AutoQASM-specific return statement functionality before
+    passing control to AutoGraph.
+    """
+    ReturnValidator(ctx).visit(node)
+    return return_statements.transform(node, ctx)

src/braket/experimental/autoqasm/transpiler/transpiler.py

@@ -36,7 +36,6 @@
     functions,
     lists,
     logical_expressions,
-    return_statements,
     slices,
     variables,
 )
@@ -59,7 +58,7 @@
     reaching_definitions,
 )
 from braket.experimental.autoqasm.autograph.tf_utils import tf_stack
-from braket.experimental.autoqasm.converters import assignments, break_statements
+from braket.experimental.autoqasm.converters import assignments, break_statements, return_statements
 
 
 class PyToOqpy(transpiler.PyToPy):

test/unit_tests/braket/experimental/autoqasm/test_api.py

@@ -839,3 +839,25 @@ def ghz(n: int):
 cnot __qubits__[0], __qubits__[4];"""
 
     assert make_ghz(5).to_ir() == expected
+
+
+def test_main_return():
+    @aq.function
+    def main() -> int:
+        return 1
+
+    with pytest.warns(UserWarning, match="Return value from top level function is ignored"):
+        main()
+
+
+def test_main_no_return():
+    @aq.function
+    def tester(x: int) -> int:
+        return measure(x)
+
+    @aq.function(num_qubits=3)
+    def main():
+        x = 3
+        tester(x)
+
+    main()