fix: Reject all files in single file drop (#641)

If multiple files were dropped and `multiple == false`,
react-dropzone will reject all files. Previously it would
accept one file and reject the rest.

BREAKING CHANGE: This can break applications that rely on the current behavior.

Closes #458

src/index.js

@@ -196,10 +196,10 @@ class Dropzone extends React.Component {
         }
       })
 
-      if (!multiple) {
+      if (!multiple && acceptedFiles.length > 1) {
         // if not in multi mode add any extra accepted files to rejected.
         // This will allow end users to easily ignore a multi file drop in "single" mode.
-        rejectedFiles.push(...acceptedFiles.splice(1))
+        rejectedFiles.push(...acceptedFiles.splice(0))
       }
 
       if (onDrop) {

src/index.spec.js

@@ -622,20 +622,14 @@ describe('Dropzone', () => {
       expect(child).toHaveProp('isDragReject', false)
     })
 
-    it('should add valid files to rejected files on a multple drop when multiple false', async () => {
-      const dropzone = mount(<Dropzone accept="image/*" onDrop={dropSpy} multiple={false} />)
-      await dropzone.simulate('drop', { dataTransfer: { files: images } })
-      const rejected = dropSpy.firstCall.args[0]
-      expect(rejected.length).toEqual(1)
-    })
-
-    it('should add invalid files to rejected when multiple is false', async () => {
+    it('should reject invalid file when multiple is false', async () => {
       const dropzone = mount(<Dropzone accept="image/*" onDrop={dropSpy} multiple={false} />)
       await dropzone.simulate('drop', {
-        dataTransfer: { files: images.concat(files) }
+        dataTransfer: { files }
       })
-      const rejected = dropSpy.firstCall.args[1]
-      expect(rejected.length).toEqual(2)
+      const [accepted, rejected] = dropSpy.firstCall.args
+      expect(rejected.length).toEqual(1)
+      expect(accepted.length).toEqual(0)
     })
 
     it('should allow single files to be dropped if multiple is false', async () => {
@@ -647,6 +641,15 @@ describe('Dropzone', () => {
       expect(rejected.length).toEqual(0)
     })
 
+    it('should reject multiple files to be dropped if multiple is false', async () => {
+      const dropzone = mount(<Dropzone accept="image/*" onDrop={dropSpy} multiple={false} />)
+
+      await dropzone.simulate('drop', { dataTransfer: { files: images } })
+      const [accepted, rejected] = dropSpy.firstCall.args
+      expect(accepted.length).toEqual(0)
+      expect(rejected.length).toEqual(2)
+    })
+
     it('should take all dropped files if multiple is true', async () => {
       const dropzone = mount(<Dropzone onDrop={dropSpy} multiple />)
       await dropzone.simulate('drop', { dataTransfer: { files: images } })