Allow specifying test case outputs using comments

Author: JukkaL

mypyc/test-data/annotate-basic.test

@@ -1,26 +1,20 @@
 [case testAnnotateNonNativeAttribute]
 def f(x):
-    return x.foo
+    return x.foo  # A: Get non-native attribute "foo".
 
 class C:
     foo: int
 
 def g(x: C) -> int:
     return x.foo
-[out]
-2: Get non-native attribute "foo".
 
 [case testAnnotateGenericAdd]
 def f(x):
-    return x + 1
+    return x + 1  # A: Generic "+" operation.
 
 def g(x: int) -> int:
     return x + 1
-[out]
-2: Generic "+" operation.
 
 [case testAnnotateTwoOperationsOnLine]
 def f(x):
-    return x.foo + 1
-[out]
-2: Get non-native attribute "foo". Generic "+" operation.
+    return x.foo + 1  # A: Get non-native attribute "foo". Generic "+" operation.

mypyc/test/test_annotate.py

@@ -34,15 +34,22 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
             return
         with use_custom_builtins(os.path.join(self.data_prefix, ICODE_GEN_BUILTINS), testcase):
             expected_output = remove_comment_lines(testcase.output)
+
+            # Parse "# A: <message>" comments.
+            for i, line in enumerate(testcase.input):
+                if "# A:" in line:
+                    msg = line.rpartition("# A:")[2].strip()
+                    expected_output.append(f"{i + 1}: {msg}")
+
             try:
                 ir, tree = build_ir_for_single_file2(testcase.input, options)
             except CompileError as e:
                 actual = e.messages
             else:
                 annotations = generate_annotations("native.py", tree, ir)
                 actual = []
-                for line, line_anns in annotations.annotations.items():
+                for line_num, line_anns in annotations.annotations.items():
                     s = " ".join(line_anns)
-                    actual.append(f"{line}: {s}")
+                    actual.append(f"{line_num}: {s}")
 
             assert_test_output(testcase, actual, "Invalid source code output", expected_output)