feature: rich info error

src/util/error.js

@@ -1,46 +1,58 @@
-function TokenizationError(message, input, line) {
-    if(Error.captureStackTrace){
+const _ = require('./underscore.js');
+
+function TokenizationError(message, token) {
+    if (Error.captureStackTrace) {
         Error.captureStackTrace(this, this.constructor);
     }
     this.name = this.constructor.name;
 
-    this.message = message;
-    this.input = input;
-    this.line = line;
+    this.input = token.input;
+    this.line = token.line;
+
+    var context = mkContext(token.input, token.line);
+    this.message = message + '\n' + context;
 }
 TokenizationError.prototype = Object.create(Error.prototype);
 TokenizationError.prototype.constructor = TokenizationError;
 
-function ParseError(message, input, line, e) {
-    if(Error.captureStackTrace){
-        Error.captureStackTrace(this, this.constructor);
-    } else{
-        this.stack = "";
-    }
-    this.stack += (this.stack ? "\nFrom " : "From ") + e.stack;
-
+function ParseError(e, token) {
     this.name = this.constructor.name;
-    this.originalError = e;
+    this.stack = e.stack;
 
-    this.message = message;
-    this.input = input;
-    this.line = line;
+    this.input = token.input;
+    this.line = token.line;
+
+    var context = mkContext(token.input, token.line);
+    this.message = e.message + '\n' + context;
 }
 ParseError.prototype = Object.create(Error.prototype);
 ParseError.prototype.constructor = ParseError;
 
-function RenderBreak(message){
-    if(Error.captureStackTrace){
+function RenderError(e, tpl) {
+    this.name = this.constructor.name;
+    this.stack = e.stack;
+
+    this.input = tpl.token.input;
+    this.line = tpl.token.line;
+
+    var context = mkContext(tpl.token.input, tpl.token.line);
+    this.message = e.message + '\n' + context;
+}
+RenderError.prototype = Object.create(Error.prototype);
+RenderError.prototype.constructor = RenderError;
+
+function RenderBreakError(message) {
+    if (Error.captureStackTrace) {
         Error.captureStackTrace(this, this.constructor);
     }
     this.name = this.constructor.name;
-    this.message = message;
+    this.message = message || '';
 }
-RenderBreak.prototype = Object.create(Error.prototype);
-RenderBreak.prototype.constructor = RenderBreak;
+RenderBreakError.prototype = Object.create(Error.prototype);
+RenderBreakError.prototype.constructor = RenderBreakError;
 
-function AssertionError(message){
-    if(Error.captureStackTrace){
+function AssertionError(message) {
+    if (Error.captureStackTrace) {
         Error.captureStackTrace(this, this.constructor);
     }
     this.name = this.constructor.name;
@@ -49,6 +61,35 @@ function AssertionError(message){
 AssertionError.prototype = Object.create(Error.prototype);
 AssertionError.prototype.constructor = AssertionError;
 
+function mkContext(input, line) {
+    var lines = input.split('\n');
+    var begin = Math.max(line - 2, 1);
+    var end = Math.min(line + 3, lines.length);
+
+    var context = _
+        .range(begin, end + 1)
+        .map(l => [
+            (l === line) ? '>> ' : '   ',
+            align(l, end),
+            '| ',
+            lines[l - 1]
+        ].join(''))
+        .join('\n');
+
+    return context;
+}
+
+function align(n, max) {
+    var length = (max + '').length;
+    var str = n + '';
+    var blank = Array(length - str.length).join(' ');
+    return blank + str;
+}
+
 module.exports = {
-    TokenizationError, ParseError, RenderBreak, AssertionError
+    TokenizationError,
+    ParseError,
+    RenderBreakError,
+    AssertionError,
+    RenderError
 };

src/util/underscore.js

@@ -7,6 +7,13 @@ function isString(value) {
     return value instanceof String || typeof value === 'string';
 }
 
+function isError(value) {
+    var signature = Object.prototype.toString.call(value);
+    // [object XXXError]
+    return signature.substr(-6, 5) === 'Error' ||
+        (typeof value.message == 'string' && typeof value.name == 'string');
+}
+
 /*
  * Iterates over own enumerable string keyed properties of an object and invokes iteratee for each property. 
  * The iteratee is invoked with three arguments: (value, key, object). 
@@ -88,9 +95,34 @@ function isObject(value) {
     return value !== null && typeof value === 'object';
 }
 
+/*
+ * A function to create flexibly-numbered lists of integers, 
+ * handy for each and map loops. start, if omitted, defaults to 0; step defaults to 1. 
+ * Returns a list of integers from start (inclusive) to stop (exclusive), 
+ * incremented (or decremented) by step, exclusive. 
+ * Note that ranges that stop before they start are considered to be zero-length instead of 
+ * negative — if you'd like a negative range, use a negative step.
+ */
+function range(start, stop, step) {
+    if (arguments.length === 1) {
+        stop = start;
+        start = 0;
+    }
+    step = step || 1;
+
+    var arr = [];
+    for (var i = start; i < stop; i += step) {
+        arr.push(i);
+    }
+    return arr;
+}
+
 exports.isString = isString;
 exports.isArray = isArray;
 exports.isObject = isObject;
+exports.isError = isError;
+
+exports.range = range;
 
 exports.forOwn = forOwn;
 exports.assign = assign;