Add source of the error (gnu like message)

Close #3

CHANGELOG.md

@@ -1,11 +1,14 @@
-# 2.0.1 - 2014-08-10
+# 2.1.0 - 2014-10-15
+
+- Add source of the error (gnu like message) (fix [#3](https://github.com/postcss/postcss-calc/issues/3))
 
-* Correctly ignore unrecognized values (fix [#2](https://github.com/postcss/postcss-calc/issues/2))
+# 2.0.1 - 2014-08-10
 
+- Correctly ignore unrecognized values (fix [#2](https://github.com/postcss/postcss-calc/issues/2))
 
 # 2.0.0 - 2014-08-06
 
-* Plugin now return a function to have a consistent api. ([ref 1](https://github.com/ianstormtaylor/rework-color-function/issues/6), [ref 2](https://twitter.com/jongleberry/status/496552790416576513))
+- Plugin now return a function to have a consistent api. ([ref 1](https://github.com/ianstormtaylor/rework-color-function/issues/6), [ref 2](https://twitter.com/jongleberry/status/496552790416576513))
 
 # 1.0.0 - 2014-08-04
 

index.js

@@ -17,7 +17,7 @@ module.exports = function plugin() {
         dec.value = transform(dec.value)
       }
       catch (err) {
-        err.position = dec.position
+        err.message = gnuMessage(err.message, dec.source)
         throw err
       }
     })
@@ -37,3 +37,13 @@ function transform(string) {
 
   return reduceCSSCalc(string)
 }
+
+/**
+ * return GNU style message
+ *
+ * @param {String} message
+ * @param {Object} source
+ */
+function gnuMessage(message, source) {
+  return (source ? (source.file ? source.file : "<css input>") + ":" + source.start.line + ":" + source.start.column : "") + " " + message
+}