Allow collections through metadata alone

lib/index.js

@@ -36,6 +36,11 @@ function plugin(opts){
       debug('checking file: %s', file);
       var data = files[file];
       match(file, data).forEach(function(key){
+        if (key && ~~keys.indexOf(key)){
+          opts[key] = {};
+          keys.push(key);
+        }
+
         metadata[key] = metadata[key] || [];
         metadata[key].push(data);
       });
@@ -158,7 +163,10 @@ function matcher(cols){
       var collection = data.collection;
       if (!Array.isArray(collection)) collection = [collection];
       collection.forEach(function(key){
-        if (key && ~keys.indexOf(key)) matches.push(key);
+        matches.push(key);
+
+        if (key && ~~keys.indexOf(key))
+          debug('adding new collection through metadata: %s', key);
       });
     }
     else {

test/fixtures/noconfig/src/four.md

@@ -0,0 +1,3 @@
+---
+collection: books
+---

test/fixtures/noconfig/src/one.md

@@ -0,0 +1,3 @@
+---
+collection: books
+---

test/fixtures/noconfig/src/three.md

@@ -0,0 +1,3 @@
+---
+collection: movies
+---

test/fixtures/noconfig/src/two.md

@@ -0,0 +1 @@
+Nothing

test/index.js

@@ -211,4 +211,19 @@ describe('metalsmith-collections', function(){
       });
   });
 
+  it('should allow collections through metadata alone', function (done) {
+    var metalsmith = Metalsmith('test/fixtures/noconfig');
+    metalsmith
+      .use(collections({ movies: {} }))
+      .build(function(err){
+        if (err) return done(err);
+        var m = metalsmith.metadata();
+        assert.equal(2, m.books.length);
+        assert.equal(1, m.movies.length);
+        assert.equal(m.collections.books, m.books);
+        assert.equal(m.collections.movies, m.movies);
+        done();
+      });
+  });
+
 });