Fix confusing ReadError traceback

Avoids confusing tracebacks when ReadErrors exceptions are raised
from the yaml reader.

Now we do print the filename that failed to load and stop processing
in order to avoid additional exceptions.

Also adds tests to prevent future regressions.

Fixes: #261

yamllint/linter.py

@@ -186,6 +186,15 @@ def get_syntax_error(buffer):
                               'syntax error: ' + e.problem + ' (syntax)')
         problem.level = 'error'
         return problem
+    except yaml.reader.ReaderError as e:
+        # we need to convert position into line+column
+        line = buffer.count('\n', 0, e.position)
+        col = e.position - (buffer.rindex('\n', 0, e.position) if line else 1)
+        problem = LintProblem(line + 1,
+                              col,
+                              'syntax error: ' + e.reason + ' (syntax)')
+        problem.level = 'error'
+        return problem
 
 
 def _run(buffer, conf, filepath):

yamllint/parser.py

@@ -121,9 +121,9 @@ def comments_between_tokens(token1, token2):
 
 
 def token_or_comment_generator(buffer):
-    yaml_loader = yaml.BaseLoader(buffer)
 
     try:
+        yaml_loader = yaml.BaseLoader(buffer)
         prev = None
         curr = yaml_loader.get_token()
         while curr is not None:
@@ -139,7 +139,8 @@ def token_or_comment_generator(buffer):
             prev = curr
             curr = next
 
-    except yaml.scanner.ScannerError:
+    # errors like this are already analysed by get_syntax_error
+    except (yaml.scanner.ScannerError, yaml.reader.ReaderError):
         pass