Merge pyflakes-syntaxerrors-2885

Author: exarkun
Reviewer: jonathanj
Fixes: #2885

Use the builtin compile function to check for syntax errors before trying to
construct an ast with the compiler package.  The compiler package is less well
able to report such errors (in particular, on Python 2.4 and older, it entirely
misses some syntax errors).

Author: exarkun

pyflakes/scripts/pyflakes.py

@@ -9,17 +9,13 @@
 checker = __import__('pyflakes.checker').checker
 
 def check(codeString, filename):
+    # Since compiler.parse does not reliably report syntax errors, use the
+    # built in compiler first to detect those.
     try:
-        tree = compiler.parse(codeString)
+        compile(codeString, filename, "exec")
     except (SyntaxError, IndentationError), value:
         msg = value.args[0]
 
-        if not value.lineno:
-            try:
-                compile(codeString, filename, 'exec')
-            except SyntaxError, value:
-                pass
-
         (lineno, offset, text) = value.lineno, value.offset, value.text
 
         line = text.splitlines()[-1]
@@ -35,6 +31,9 @@ def check(codeString, filename):
 
         return 1
     else:
+        # Okay, it's syntactically valid.  Now parse it into an ast and check
+        # it.
+        tree = compiler.parse(codeString)
         w = checker.Checker(tree, filename)
         w.messages.sort(lambda a, b: cmp(a.lineno, b.lineno))
         for warning in w.messages: