Fix bug in ldflags_to_sanitizers.py.

The Python tests were passing because we only tested the individual
functions, not the program as a whole.

The run_tests.py tests were passing because errors from $(shell) do
not cause the build to fail; ndk-build just ended up parsing the
error message and not finding any sanitizers.

The asan-smoke test passed because A) I hadn't run `./run_tests.py
--clean-device` to purge the old tests, so the libraries were still
on the device and B) running the tests in the r17 branch had led to
asan_device_setup running again, installing the libraries to the
system partition once again.

Test: nose2 build
Test: ./run_tests.py --clean-device  # After purging asan /system libs
Bug: android/ndk#540
Change-Id: I85a30cc198be4a0f39548271f56112835805ca76

build/ldflags_to_sanitizers.py

@@ -52,18 +52,18 @@ def argv_to_module_arg_lists(args):
     return modules[0], modules[1:]
 
 
-def main(argv):
+def main(argv, stream=sys.stdout):
     """Program entry point."""
     if len(argv) < 4:
         sys.exit(
             'usage: ldflags_to_sanitizers.py GLOBAL_FLAGS '
             '--module MODULE_FLAGS [--module MODULE_FLAGS...]')
 
-    all_sanitizers = list(sanitizers_from_args(sys.argv[1]))
-    modules_flags = argv_to_module_arg_lists(argv[2:])
+    global_flags, modules_flags = argv_to_module_arg_lists(argv[1:])
+    all_sanitizers = list(sanitizers_from_args(global_flags))
     for module_flags in modules_flags:
         all_sanitizers.extend(sanitizers_from_args(module_flags))
-    print(' '.join(sorted(set(all_sanitizers))))
+    print(' '.join(sorted(set(all_sanitizers))), file=stream)
 
 
 if __name__ == '__main__':

build/test_ldflags_to_sanitizers.py

@@ -18,7 +18,13 @@
 from __future__ import absolute_import
 import unittest
 
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
+
 from build.ldflags_to_sanitizers import argv_to_module_arg_lists
+from build.ldflags_to_sanitizers import main as ldflags_main
 from build.ldflags_to_sanitizers import sanitizers_from_args
 
 
@@ -87,3 +93,12 @@ def test_argv_to_module_arg_lists(self):
         self.assertTupleEqual(
             (['foo', 'bar'], [['baz']]),
             argv_to_module_arg_lists(['foo', 'bar', '--module', 'baz']))
+
+    def test_main(self):
+        """Test that the program itself works."""
+        sio = StringIO()
+        ldflags_main(
+            ['ldflags_to_sanitizers.py', '-fsanitize=undefined', '--module',
+             '-fsanitize=address,thread', '-fno-sanitize=thread',
+             '--module', '-fsanitize=undefined'], sio)
+        self.assertEqual('address undefined', sio.getvalue().strip())