From c5d7445973dc126ed48a7ac5c98de8fb5fa7ad2a Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 21 Apr 2017 18:11:14 +0000
Subject: [PATCH] compiler: reject reachable implicit return if not returning
 TNone.

Fixes #718.
---
 artiq/compiler/transforms/artiq_ir_generator.py       | 8 ++++++++
 artiq/test/lit/codegen/error_illegal_return.py        | 9 +++++++++
 artiq/test/lit/codegen/unreachable_implicit_return.py | 9 +++++++++
 3 files changed, 26 insertions(+)
 create mode 100644 artiq/test/lit/codegen/error_illegal_return.py
 create mode 100644 artiq/test/lit/codegen/unreachable_implicit_return.py

diff --git a/artiq/compiler/transforms/artiq_ir_generator.py b/artiq/compiler/transforms/artiq_ir_generator.py
index aea58f0d5..98fc8a90e 100644
--- a/artiq/compiler/transforms/artiq_ir_generator.py
+++ b/artiq/compiler/transforms/artiq_ir_generator.py
@@ -317,7 +317,15 @@ class ARTIQIRGenerator(algorithm.Visitor):
                     self.current_block.append(ir.Return(ir.Constant(None, builtins.TNone())))
             else:
                 if not self.current_block.is_terminated():
+                    if len(self.current_block.predecessors()) != 0:
+                        diag = diagnostic.Diagnostic("error",
+                            "this function must return a value of type {typ} explicitly",
+                            {"typ": types.TypePrinter().name(typ.ret)},
+                            node.keyword_loc)
+                        self.engine.process(diag)
+
                     self.current_block.append(ir.Unreachable())
+
         finally:
             self.name = old_name
             self.current_args = old_args
diff --git a/artiq/test/lit/codegen/error_illegal_return.py b/artiq/test/lit/codegen/error_illegal_return.py
new file mode 100644
index 000000000..5e15cade7
--- /dev/null
+++ b/artiq/test/lit/codegen/error_illegal_return.py
@@ -0,0 +1,9 @@
+# RUN: %python -m artiq.compiler.testbench.signature +diag %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+# CHECK-L: ${LINE:+1}: error: this function must return a value of type numpy.int32 explicitly
+def foo(x):
+    if x:
+        return 1
+
+foo(True)
diff --git a/artiq/test/lit/codegen/unreachable_implicit_return.py b/artiq/test/lit/codegen/unreachable_implicit_return.py
new file mode 100644
index 000000000..a434f8a28
--- /dev/null
+++ b/artiq/test/lit/codegen/unreachable_implicit_return.py
@@ -0,0 +1,9 @@
+# RUN: %python -m artiq.compiler.testbench.signature %s
+
+def foo(x):
+    if x:
+        return 1
+    else:
+        return 2
+
+foo(True)