1 files changed, 61 insertions, 0 deletions
diff --git a/scss/errors.py b/scss/errors.py
new file mode 100644
index 0000000..6e946e5
--- /dev/null
+++ b/scss/errors.py
@@ -0,0 +1,61 @@
+import sys
+import traceback
+
+class SassError(Exception):
+    """Error class that wraps another exception and attempts to bolt on some
+    useful context.
+    """
+    def __init__(self, exc, rule=None, expression=None):
+        self.exc = exc
+        self.rule = rule
+        self.expression = expression
+        _, _, self.original_traceback = sys.exc_info()
+
+    def set_rule(self, rule):
+        """Set the current rule.
+
+        If this error already has a rule, it's left alone; this is because
+        exceptions propagate outwards and so the first rule seen is the
+        "innermost".
+        """
+        if not self.rule:
+            self.rule = rule
+
+    def format_prefix(self):
+        # TODO pointer, yadda
+        # TODO newlines, yadda
+        if self.rule:
+            return "Error parsing block:\n" + "    " + self.rule.unparsed_contents
+        else:
+            return "Unknown error"
+
+    def __str__(self):
+        prefix = self.format_prefix()
+
+        ret = [prefix, "\n\n"]
+
+        if self.rule:
+            ret.extend(("From ", self.rule.file_and_line, "\n\n"))
+
+        ret.append("Traceback:\n")
+        ret.extend(traceback.format_tb(self.original_traceback))
+        ret.extend((type(self.exc).__name__, ": ", str(self.exc), "\n"))
+        return ''.join(ret)
+
+class SassParseError(SassError):
+    """Error raised when parsing a Sass expression fails."""
+
+    def format_prefix(self):
+        # TODO pointer
+        # TODO deal with newlines, etc
+        return """Error parsing expression:\n    %s""" % (self.expression,)
+
+
+class SassEvaluationError(SassError):
+    """Error raised when evaluating a parsed expression fails."""
+
+    def format_prefix(self):
+        # TODO pointer
+        # TODO ast needs to know where each node came from for that to work  :(
+        # TODO deal with newlines, etc
+        return """Error evaluating expression:\n    %s""" % (self.expression,)