JSComplexityBear: Handle invalid syntax better

Ths commits adds the feature to this bear to give a result when the tool
is unable to parse the code at all. This is given as a MAJOR error as
this a fault in the javascript code in itself.

Fixes #729

Author: AbdealiLoKo

bears/js/JSComplexityBear.py

@@ -1,7 +1,9 @@
 import json
+import re
 
 from coalib.bearlib.abstractions.Linter import linter
 from coalib.bears.requirements.NpmRequirement import NpmRequirement
+from coalib.results.RESULT_SEVERITY import RESULT_SEVERITY
 from coalib.results.Result import Result
 
 
@@ -19,6 +21,11 @@ class JSComplexityBear:
     ASCIINEMA_URL = 'https://asciinema.org/a/39250'
     CAN_DETECT = {'Complexity'}
 
+    try:
+        DecodeError = json.decoder.JSONDecodeError
+    except AttributeError:
+        DecodeError = ValueError
+
     @staticmethod
     def create_arguments(filename, file, config_file):
         return '--format', 'json', filename
@@ -29,7 +36,20 @@ def process_output(self, output, filename, file, cc_threshold: int=10):
         """
         message = "{} has a cyclomatic complexity of {}."
         if output:
-            output = json.loads(output)
+            try:
+                output = json.loads(output)
+            except self.DecodeError:
+                output_regex = (r'Fatal error \[getReports\]: .+: '
+                                r'Line (?P<line>\d+): (?P<message>.*)')
+                for match in re.finditer(output_regex, output):
+                    groups = match.groupdict()
+                    yield Result.from_values(
+                        origin=self,
+                        message=groups["message"].strip(),
+                        file=filename,
+                        severity=RESULT_SEVERITY.MAJOR,
+                        line=int(groups["line"]))
+                return
             for function in output["reports"][0]["functions"]:
                 if function["cyclomatic"] >= cc_threshold:
                     yield Result.from_values(

tests/js/JSComplexityBearTest.py

@@ -36,10 +36,12 @@
 })()
 """
 
+test_syntax_error = '{<!@3@^ yeah!/\n'
+
 JSComplexityBearTest = verify_local_bear(
     JSComplexityBear,
     valid_files=(complexity_4,),
-    invalid_files=(complexity_12,),
+    invalid_files=(complexity_12, test_syntax_error),
     tempfile_kwargs={"suffix": ".js"})
 
 JSComplexityBearThresholdTest = verify_local_bear(