Add 'polite' YAML syntax validation and hinting

lib/ansible/errors.py

@@ -30,3 +30,5 @@ class AnsibleFileNotFound(AnsibleError):
 class AnsibleConnectionFailed(AnsibleError):
     pass
 
+class AnsibleYAMLValidationFailed(AnsibleError):
+    pass

lib/ansible/utils.py

@@ -229,9 +229,29 @@ def parse_yaml_from_file(path):
 
     try:
         data = file(path).read()
+        return parse_yaml(data)
     except IOError:
         raise errors.AnsibleError("file not found: %s" % path)
-    return parse_yaml(data)
+    except yaml.YAMLError, exc:
+        if hasattr(exc, 'problem_mark'):
+            mark = exc.problem_mark
+            if mark.line -1 >= 0:
+                before_probline = data.split("\n")[mark.line-1]
+            else:
+                before_probline = ''
+            probline = data.split("\n")[mark.line]
+            arrow = " " * mark.column + "^"
+            msg = """Syntax Error while loading YAML script, %s
+Note: The error may actually appear before this position: line %s, column %s
+
+%s
+%s
+%s""" % (path, mark.line + 1, mark.column + 1, before_probline, probline, arrow)
+        else:
+            # No problem markers means we have to throw a generic
+            # "stuff messed up" type message. Sry bud.
+            msg = "Could not parse YAML. Check over %s again." % path
+        raise errors.AnsibleYAMLValidationFailed(msg)
 
 def parse_kv(args):
     ''' convert a string of key/value items to a dict '''