YapfBear: Catch parse errors and give result

The YapfBear earlier raised an error when the file was not parseable.
Now, that error is caught and a Result is given out mentioning that the
file has syntax errors and cannot be parsed.

Fixes #750

Author: AbdealiLoKo

bears/python/YapfBear.py

@@ -144,11 +144,17 @@ def run(self, filename, file,
         options += 'use_tabs = ' + str(not use_spaces)
         options = options.format(**locals())
 
-        with prepare_file(options.splitlines(keepends=True),
-                          None) as (file_, fname):
-            corrected = FormatFile(filename,
-                                   style_config=fname,
-                                   verify=False)[0].splitlines(True)
+        try:
+            with prepare_file(options.splitlines(keepends=True),
+                              None) as (file_, fname):
+                corrected = FormatFile(filename,
+                                       style_config=fname,
+                                       verify=False)[0].splitlines(True)
+        except SyntaxError:
+            yield Result.from_values(
+                self, "The code cannot be parsed due to syntax errors.",
+                filename)
+            return
         diffs = Diff.from_string_arrays(file, corrected).split_diff()
         for diff in diffs:
             yield Result(self,

tests/python/YapfBearTest.py

@@ -31,6 +31,11 @@ def test_eof_handling(self):
         self.check_validity(self.uut, ['a = 2'], valid=True)
         self.check_validity(self.uut, ['\n'], valid=True)
 
+    def test_invalid_python(self):
+        self.check_validity(self.uut, ['cout << "hello";\n'], valid=False)
+        self.check_validity(self.uut, ['def a():', ' b=1', '  bad indent'],
+                            valid=False)
+
     def test_valid_python_2(self):
         self.check_validity(self.uut, ['print 1\n'], valid=True)