added patternExtension property to provide method for limiting which files are considered patterns

.gitignore

@@ -1 +1,2 @@
-node_modules
+node_modules
+debug.log

lib/helpers/read-partials.js

@@ -18,7 +18,7 @@ module.exports = readPartials;
  * @param {Object} metalsmith
  * @return {Object}
  */
-function readPartials(partialsPath, layoutsPath, metalsmith) {
+function readPartials(partialsPath, partialExtension, layoutsPath, metalsmith) {
   var partialsAbs = path.isAbsolute(partialsPath) ? partialsPath : path.join(metalsmith.path(), partialsPath);
   var layoutsAbs = path.isAbsolute(layoutsPath) ? layoutsPath : path.join(metalsmith.path(), layoutsPath);
   var files = read(partialsAbs);
@@ -35,8 +35,9 @@ function readPartials(partialsPath, layoutsPath, metalsmith) {
     var name = path.join(fileInfo.dir, fileInfo.name);
     var partialAbs = path.join(partialsAbs, name);
     var partialPath = path.relative(layoutsAbs, partialAbs);
-
+    if (!partialExtension || fileInfo.ext == partialExtension) {
-    partials[name.replace(/\\/g, '/')] = partialPath;
+      partials[name.replace(/\\/g, '/')] = partialPath; 
+    }
   }
 
   return partials;

lib/index.js

@@ -29,6 +29,7 @@ var settings = [
   'directory',
   'engine',
   'partials',
+  'partialExtension',
   'pattern',
   'rename',
   'exposeConsolidate'
@@ -42,6 +43,7 @@ var settings = [
  *   @property {String} directory (optional)
  *   @property {String} engine
  *   @property {String} partials (optional)
+ *   @property {String} partialExtension (optional)
  *   @property {String} pattern (optional)
  *   @property {Boolean} rename (optional)
  * @return {Function}
@@ -75,6 +77,7 @@ function plugin(opts){
   var def = opts.default;
   var dir = opts.directory || 'layouts';
   var engine = opts.engine;
+  var partialExtension = opts.partialExtension;
   var partials = opts.partials;
   var pattern = opts.pattern;
   var rename = opts.rename;
@@ -94,7 +97,7 @@ function plugin(opts){
      */
     if (partials) {
       if (typeof partials === 'string') {
-        params.partials = readPartials(partials, dir, metalsmith);
+        params.partials = readPartials(partials, partialExtension, dir, metalsmith);
       } else {
         params.partials = partials;
       }

test/fixtures/partials-partialExtension/build/index.html

@@ -0,0 +1,3 @@
+<p>Nav</p>
+<p>Content</p>
+

test/fixtures/partials-partialExtension/expected/index.html

@@ -0,0 +1,3 @@
+<p>Nav</p>
+<p>Content</p>
+

test/fixtures/partials-partialExtension/layouts/layout.html

@@ -0,0 +1,2 @@
+{{>nested/nav}}
+{{{contents}}}

test/fixtures/partials-partialExtension/layouts/partials/nested/nav.config.yaml

@@ -0,0 +1 @@
+foo: bar

test/fixtures/partials-partialExtension/layouts/partials/nested/nav.html

@@ -0,0 +1 @@
+<p>Nav</p>

test/fixtures/partials-partialExtension/src/index.html

@@ -0,0 +1,4 @@
+---
+layout: layout.html
+---
+<p>Content</p>

test/index.js

@@ -135,6 +135,24 @@ describe('metalsmith-layouts', function(){
     });
   });
 
+   it('should use partialExtension to limit the matching partial files', function(done){
+     // Without partialExtension the nav.config.yaml would cause an error
+    var instance = Metalsmith('test/fixtures/partials-partialExtension')
+      .use(layouts({
+        engine: 'handlebars',
+        partials: 'layouts/partials',
+        partialExtension: '.html'
+      }));
+
+    instance.build(function(err){
+      if (err) {
+        return done(err);
+      }
+      equal('test/fixtures/partials-partialExtension/expected', 'test/fixtures/partials-partialExtension/build');
+      done();
+    });
+  });
+
   it('should find partials in subdirectories correctly', function(done){
     // This test would only fail on Windows if readPartials did not
     // replace backslashes in partial names