Rewrite syntax errors handling and test them

If a syntax errors occurs at the same place than a regular yamllint rule
error, only the yamllint one is issued.

yamllint/__init__.py

@@ -14,7 +14,10 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import yaml
+
 from yamllint import config
+from yamllint.errors import LintProblem
 from yamllint import parser
 
 
@@ -28,23 +31,14 @@ __license__ = 'GPLv3'
 __version__ = APP_VERSION
 
 
-def _lint(buffer, conf):
+def get_costemic_problems(buffer, conf):
     rules = config.get_enabled_rules(conf)
 
     # Split token rules from line rules
     token_rules = [r for r in rules if r.TYPE == 'token']
     line_rules = [r for r in rules if r.TYPE == 'line']
 
-    # If the document contains a syntax error, save it and yield it at the
-    # right line
-    syntax_error = parser.get_syntax_error(buffer)
-
     for elem in parser.token_or_line_generator(buffer):
-        if syntax_error and syntax_error.line <= elem.line_no:
-            syntax_error.level = 'error'
-            yield syntax_error
-            syntax_error = None
-
         if isinstance(elem, parser.Token):
             for rule in token_rules:
                 rule_conf = conf[rule.ID]
@@ -62,6 +56,39 @@ def _lint(buffer, conf):
                     yield problem
 
 
+def get_syntax_error(buffer):
+    try:
+        list(yaml.safe_load_all(buffer))
+    except yaml.error.MarkedYAMLError as e:
+        problem = LintProblem(e.problem_mark.line + 1,
+                              e.problem_mark.column + 1,
+                              'syntax error: ' + e.problem)
+        problem.level = 'error'
+        return problem
+
+
+def _lint(buffer, conf):
+    # If the document contains a syntax error, save it and yield it at the
+    # right line
+    syntax_error = get_syntax_error(buffer)
+
+    for problem in get_costemic_problems(buffer, conf):
+        # Insert the syntax error (if any) at the right place...
+        if (syntax_error and syntax_error.line <= problem.line and
+                syntax_error.column <= problem.column):
+            # ... unless there is already a yamllint error, in which case the
+            # syntax error is probably redundant.
+            if (syntax_error.line != problem.line or
+                    syntax_error.column != problem.column):
+                yield syntax_error
+            syntax_error = None
+
+        yield problem
+
+    if syntax_error:
+        yield syntax_error
+
+
 def lint(input, conf):
     """Lints a YAML source.
 

yamllint/parser.py

@@ -16,8 +16,6 @@
 
 import yaml
 
-from yamllint.errors import LintProblem
-
 
 class Line(object):
     def __init__(self, line_no, buffer, start, end):
@@ -85,11 +83,3 @@ def token_or_line_generator(buffer):
         else:
             yield token
             token = next(token_gen, None)
-
-
-def get_syntax_error(buffer):
-    try:
-        yaml.safe_load_all(buffer)
-    except yaml.error.MarkedYAMLError as e:
-        return LintProblem(e.problem_mark.line + 1, e.problem_mark.column + 1,
-                           'syntax error: ' + e.problem)