New: Add a 'did you mean?' note when failing to find a task (#94)

lib/helpers/normalizeArgs.js

@@ -4,6 +4,7 @@ var assert = require('assert');
 
 var map = require('arr-map');
 var flatten = require('arr-flatten');
+var levenshtein = require('fast-levenshtein');
 
 function normalizeArgs(registry, args) {
   function getFunction(task) {
@@ -12,7 +13,14 @@ function normalizeArgs(registry, args) {
     }
 
     var fn = registry.get(task);
-    assert(fn, 'Task never defined: ' + task);
+    if (!fn) {
+      var similar = similarTasks(registry, task);
+      if (similar.length > 0) {
+        assert(false, 'Task never defined: ' + task + ' - did you mean? ' + similar.join(', '));
+      } else {
+        assert(false, 'Task never defined: ' + task);
+      }
+    }
     return fn;
   }
 
@@ -22,4 +30,23 @@ function normalizeArgs(registry, args) {
   return map(flattenArgs, getFunction);
 }
 
+function similarTasks(registry, queryTask) {
+  if (typeof queryTask !== 'string') {
+    return [];
+  }
+
+  var tasks = registry.tasks();
+  var similarTasks = [];
+  for (var task in tasks) {
+    if (tasks.hasOwnProperty(task)) {
+      var distance = levenshtein.get(task, queryTask);
+      var allowedDistance = Math.floor(0.4 * task.length) + 1;
+      if (distance < allowedDistance) {
+        similarTasks.push(task);
+      }
+    }
+  }
+  return similarTasks;
+}
+
 module.exports = normalizeArgs;

package.json

@@ -34,7 +34,8 @@
     "last-run": "^1.1.0",
     "object.defaults": "^1.0.0",
     "object.reduce": "^1.0.0",
-    "undertaker-registry": "^1.0.0"
+    "undertaker-registry": "^1.0.0",
+    "fast-levenshtein": "^1.0.0"
   },
   "devDependencies": {
     "async-once": "^1.0.0",

test/registry.js

@@ -194,4 +194,16 @@ describe('registry', function() {
     taker.series('test')();
   });
 
+  it('should fail and offer tasks which are close in name', function(done) {
+    var taker = new Undertaker(new CommonRegistry());
+    var customRegistry = new DefaultRegistry();
+    taker.registry(customRegistry);
+
+    function fail() {
+      taker.series('clear');
+    }
+
+    expect(fail).toThrow(/Task never defined: clear - did you mean\? clean/);
+    done();
+  });
 });