Added a new Python 2/3 check for invalid raise syntax.

Close #1937

4 files changed, 55 insertions, 6 deletions

diff --git a/ChangeLog b/ChangeLog
index d26960237..1be0b2d7c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,10 @@ What's New in Pylint 1.9.0?
 
 Release date:
 
+   * Added a new Python 2/3 check for invalid raise syntax.
+
+     Close #1937
+
    * Added a new Python 2/3 check for invalid lambda parameter list, `lambda-parameter-parens`
 
      Close #1995
diff --git a/doc/whatsnew/1.9.rst b/doc/whatsnew/1.9.rst
index f9a349961..18c01b7a2 100644
--- a/doc/whatsnew/1.9.rst
+++ b/doc/whatsnew/1.9.rst
@@ -39,5 +39,19 @@ New checkers
       lambda (some_param, some_other_param): ...
 
 
+* A new Python 3 checker was added to warn about invalid raise syntax:
+
+  .. code-block:: python
+
+      raise Exception, "value", tb
+
+
+  To have this working on Python 3 as well, please use the ``six`` library:
+
+  .. code-block:: python
+
+      six.reraise(Exception, "value", tb)
+
+
 Other Changes
 =============
diff --git a/pylint/checkers/python3.py b/pylint/checkers/python3.py
index e3854dae1..2c98303ad 100644
--- a/pylint/checkers/python3.py
+++ b/pylint/checkers/python3.py
@@ -975,6 +975,11 @@ class Python3TokenChecker(checkers.BaseTokenChecker):
                   'Used when a lambda definition contains parantheses for the parameter '
                   'list. This is invalid syntax in Python 3.X.',
                   {'maxversion': (3, 0)}),
+        'E1612': ('Cannot raise on Python 3 using this raise form',
+                  'invalid-raise-syntax',
+                  'Used when an invalid raise construct that will not work on Python 3 was '
+                  'deteted.',
+                  {'maxversion': (3, 0)}),
     }
 
     def process_tokens(self, tokens):
@@ -991,12 +996,19 @@ class Python3TokenChecker(checkers.BaseTokenChecker):
                 if any(elem for elem in token if ord(elem) > 127):
                     self.add_message('non-ascii-bytes-literal', line=start[0])
 
-            if (tok_type == tokenize.NAME
-                    and token == 'lambda'
-                    and idx < len(tokens)
-                    and tokens[idx + 1][0] == tokenize.OP
-                    and tokens[idx + 1][1] == '('):
-                self.add_message('lambda-parameter-parens', line=start[0])
+            if tok_type == tokenize.NAME:
+                if (token == 'lambda'
+                        and idx < len(tokens)
+                        and tokens[idx + 1][0] == tokenize.OP
+                        and tokens[idx + 1][1] == '('):
+                    self.add_message('lambda-parameter-parens', line=start[0])
+                elif (token == 'raise'
+                        and idx < len(tokens) - 1
+                        and tokens[idx + 1][0] == tokenize.NAME
+                        and tokens[idx + 2][0] == tokenize.OP
+                        and tokens[idx + 2][1] == ','):
+                    self.add_message('invalid-raise-syntax', line=start[0])
+
 
 def register(linter):
     linter.register_checker(Python3Checker(linter))
diff --git a/pylint/test/unittest_checker_python3.py b/pylint/test/unittest_checker_python3.py
index 5e3fa7c74..7d44617c2 100644
--- a/pylint/test/unittest_checker_python3.py
+++ b/pylint/test/unittest_checker_python3.py
@@ -980,3 +980,22 @@ class TestPython3TokenChecker(testutils.CheckerTestCase):
         self._test_token_message("lambda (a): a", "lambda-parameter-parens")
         self._test_token_message("lambda(a): a", "lambda-parameter-parens")
         self._test_token_message("lambda  (a, b, c): a", "lambda-parameter-parens")
+
+    def test_invalid_raise_syntax(self):
+        self._test_token_message("raise Exception,'1', None", "invalid-raise-syntax")
+        self._test_token_message("raise  Exception,'1', None", "invalid-raise-syntax")
+        self._test_token_message("raise Exception , '1', None", "invalid-raise-syntax")
+
+        codes = [
+            "raise Exception",
+            "raise Exception;",
+            "raise 1",
+            "raise a",
+            "raise",
+            "raise Exception(2)",
+            "raise Exception('abc')",
+        ]
+        for code in codes:
+            tokens = testutils._tokenize_str(code)
+            with self.assertNoMessages():
+                self.checker.process_tokens(tokens)