Python: Fail tests when errors/warnings are logged

This is primarily useful for ensuring that errors where a node does not
have an appropriate context set in `python.tsg` actually have an effect
on the pass/fail status of the parser tests. Previously, these would
just be logged to stdout, but test could still succeed when there were
errors present.

Also fixes one of the logging lines in `tsg_parser.py` to be more
consistent with the others.

python/extractor/semmle/python/parser/dump_ast.py

@@ -97,9 +97,27 @@ class AstDumper(object):
 
 
 class StdoutLogger(logging.Logger):
+    error_count = 0
     def log(self, level, fmt, *args):
         sys.stdout.write(fmt % args + "\n")
 
+    def info(self, fmt, *args):
+        self.log(logging.INFO, fmt, *args)
+
+    def warn(self, fmt, *args):
+        self.log(logging.WARN, fmt, *args)
+        self.error_count += 1
+
+    def error(self, fmt, *args):
+        self.log(logging.ERROR, fmt, *args)
+        self.error_count += 1
+
+    def had_errors(self):
+        return self.error_count > 0
+
+    def reset_error_count(self):
+        self.error_count = 0
+
 def old_parser(inputfile, logger):
     mod = PythonSourceModule(None, inputfile, logger)
     logger.close()

python/extractor/semmle/python/parser/tsg_parser.py

@@ -440,7 +440,7 @@ def concatenate_stringparts(stringparts, logger):
     try:
         return "".join(decode_str(stringpart.s) for stringpart in stringparts)
     except Exception as ex:
-        logger.error("Unable to concatenate string %s getting error %s", stringparts, ex)
+        logger.error("Unable to concatenate string {} getting error {}".format(stringparts, ex))
         return stringparts[0].s
 
 

python/extractor/tests/test_parser.py

@@ -49,6 +49,8 @@ class ParserTest(unittest.TestCase):
             diff = e.output
         if diff:
             pytest.fail(diff.decode("utf-8"))
+        self.check_for_stdout_errors(logger)
+
         self.assertEqual(self.capsys.readouterr().err, "")
         os.remove(oldfile)
         os.remove(newfile)
@@ -84,9 +86,15 @@ class ParserTest(unittest.TestCase):
             diff = e.output
         if diff:
             pytest.fail(diff.decode("utf-8"))
+
+        self.check_for_stdout_errors(logger)
         self.assertEqual(self.capsys.readouterr().err, "")
         os.remove(actual)
 
+    def check_for_stdout_errors(self, logger):
+        if logger.had_errors():
+            logger.reset_error_count()
+            pytest.fail("Errors/warnings were logged to stdout during testing.")
 
 def setup_tests():
     test_folder = os.path.join(os.path.dirname(__file__), "parser")