Add support for clean option

Readme.md

@@ -139,6 +139,10 @@ Set the relative `path` to the source directory, or get the full one if no `path
 
 Set the relative `path` to the destination directory, or get the full one if no `path` is provided. The destination directory defaults to `./build`.
 
+#### #clean(boolean)
+
+Set whether to remove the destination directory before writing to it, or get the current setting. Defaults to `true`.
+
 #### #metadata(json)
 
 Get the global metadata. This is useful for plugins that want to set global-level metadata that can be applied to all files.

bin/metalsmith

@@ -23,9 +23,9 @@ try {
  */
 
 var metalsmith = new Metalsmith(process.cwd());
-if (json.source) metalsmith.source(json.source);
-if (json.destination) metalsmith.destination(json.destination);
-if (json.metadata) metalsmith.metadata(json.metadata);
+['source', 'destination', 'metadata', 'clean'].forEach(function(key){
+  if (json[key]) metalsmith[key](json[key]);
+});
 
 /**
  * Plugins.

lib/index.js

@@ -31,6 +31,7 @@ function Metalsmith(dir){
   this.data = {};
   this.source('src');
   this.destination('build');
+  this.clean(true);
 }
 
 /**
@@ -84,6 +85,17 @@ Metalsmith.prototype.destination = function(path){
   return this;
 };
 
+/**
+ * Get or set whether the destination directory will be removed before writing.
+ * @param  {Boolean} clean
+ * @return {Boolean or Metalsmith}
+ */
+Metalsmith.prototype.clean = function(clean){
+  if (!arguments.length) return this._clean;
+  this._clean = clean;
+  return this;
+};
+
 /**
  * Join path `strs` with the working directory.
  *
@@ -182,10 +194,18 @@ Metalsmith.prototype.read = function(fn){
 Metalsmith.prototype.write = function(files, fn){
   var dest = this.destination();
 
-  rm(dest, function(err){
-    if (err) return fn(err);
+  if (this.clean()) {
+    rm(dest, function(err){
+      if (err) return fn(err);
+      writeAll();
+    });
+  } else {
+    writeAll();
+  }
+
+  function writeAll(){
     each(Object.keys(files), write, fn);
-  });
+  }
 
   function write(file, done){
     var data = files[file];

test/fixtures/write-noclean/expected/index.md

@@ -0,0 +1 @@
+body

test/index.js

@@ -35,6 +35,11 @@ describe('Metalsmith', function(){
     assert('build' == m._dest);
   });
 
+  it('should default clean to true', function(){
+    var m = Metalsmith('test/tmp');
+    assert(true === m._clean);
+  });
+
   describe('#use', function(){
     it('should add a plugin to the middleware stack', function(){
       var m = Metalsmith('test/tmp');
@@ -69,6 +74,19 @@ describe('Metalsmith', function(){
     });
   });
 
+  describe('#clean', function(){
+    it('should set the clean option', function(){
+      var m = Metalsmith('test/tmp');
+      m.clean(false);
+      assert(false === m._clean);
+    });
+
+    it('should get the value of the clean option', function(){
+      var m = Metalsmith('test/tmp');
+      assert(true === m.clean());
+    });
+  });
+
   describe('#metadata', function(){
     it('should get metadata', function(){
       var m = Metalsmith('test/tmp');
@@ -147,6 +165,20 @@ describe('Metalsmith', function(){
       });
     });
 
+    it('should not remove existing destination directory if clean is false', function(done){
+      var m = Metalsmith('test/fixtures/write-noclean');
+      m.clean(false);
+      exec('mkdir -p test/fixtures/write-noclean/build && touch test/fixtures/write-noclean/build/empty.md', function(err){
+        if (err) return done(err);
+        var files = { 'index.md': { contents: new Buffer('body') }};
+        m.write(files, function(err){
+          if (err) return done(err);
+          equal('test/fixtures/write-noclean/build', 'test/fixtures/write-noclean/expected');
+          done();
+        });
+      });
+    });
+
     it('should chmod an optional mode from file metadata', function(done){
       var m = Metalsmith('test/fixtures/write-mode');
       var files = {