Update setPath to work with custom files

spec/text-buffer-io-spec.js

@@ -249,9 +249,10 @@ describe('TextBuffer IO', () => {
 
   describe('.save', () => {
     let filePath
+    let tempDir
 
     beforeEach(() => {
-      const tempDir = temp.mkdirSync()
+      tempDir = temp.mkdirSync()
       filePath = path.join(tempDir, 'temp.txt')
       fs.writeFileSync(filePath, '')
       buffer = new TextBuffer()
@@ -430,6 +431,17 @@ describe('TextBuffer IO', () => {
           done()
         }, buffer.fileChangeDelay))
       })
+
+      it('passes setPath to the custom File object', (done) => {
+        const newPath = path.join(tempDir, 'temp2.txt')
+        fs.writeFileSync(newPath, '')
+        buffer.setPath(newPath)
+        buffer.setText('test')
+        buffer.save().then(() => {
+          expect(fs.readFileSync(newPath, 'utf8')).toEqual('TEST')
+          done()
+        })
+      })
     })
 
     describe('when a permission error occurs', () => {
@@ -1153,6 +1165,10 @@ class ReverseCaseFile {
     return this.path
   }
 
+  setPath (path) {
+    this.path = path
+  }
+
   createReadStream () {
     return fs.createReadStream(this.path).pipe(new Transform({
       transform (chunk, encoding, callback) {

src/text-buffer.coffee

@@ -566,6 +566,10 @@ class TextBuffer
   # * `filePath` A {String} representing the new file path
   setPath: (filePath) ->
     return if filePath is @getPath()
+    if @file? and filePath
+      @file.setPath filePath
+      @updateFilePath()
+      return
     @setFile(new File(filePath) if filePath)
 
   # Experimental: Set a custom {File} object as the buffer's backing store.
@@ -588,8 +592,11 @@ class TextBuffer
   setFile: (file) ->
     return if file?.getPath() is @getPath()
     @file = file
+    @file?.setEncoding?(@getEncoding())
+    @updateFilePath()
+
+  updateFilePath: ->
     if @file?
-      @file.setEncoding?(@getEncoding())
       @subscribeToFile()
     @emitter.emit 'did-change-path', @getPath()