fix grunt.file.expandMapping related issue

gruntjs/gruntjs-tests.ts

@@ -57,4 +57,8 @@ exports = (grunt: IGrunt) => {
     asyncedTwoArgs(2, "values", (result: string) => {
         console.log(result);
     });
+    var fileMaps = grunt.file.expandMapping([''], '', { ext: '.js' });
+    fileMaps.length;
+    fileMaps[0].src.length;
+    fileMaps[0].dest;
 };

gruntjs/gruntjs.d.ts

@@ -450,7 +450,7 @@ declare module grunt {
              * @see FileModule.expand method documentation for an explanation of how the patterns
              *      and options arguments may be specified.
              */
-            expandMapping(patterns: string[], dest: string, options: IExpandedFilesConfig): IFilesMap
+            expandMapping(patterns: string[], dest: string, options: IExpandedFilesConfig): Array<IFileMap>
 
             /**
              * Match one or more globbing patterns against one or more file paths.
@@ -558,7 +558,7 @@ declare module grunt {
             /**
              * Pattern(s) to match, relative to the {@link IExpandedFilesConfig.cwd}.
              */
-            src: string[]
+            src?: string[]
 
             /**
              * Destination path prefix.
@@ -599,7 +599,7 @@ declare module grunt {
             /**
              * Enables the following options
              */
-            expand: boolean // = true
+            expand?: boolean // = true
 
             /**
              * All {@link IExpandedFilesConfig.src} matches are relative to (but don't include) this path.
@@ -609,7 +609,7 @@ declare module grunt {
             /**
              * Replace any existing extension with this value in generated {@link IExpandedFilesConfig.dest} paths.
              */
-            ext?: boolean
+            ext?: string
 
             /**
              * Remove all path parts from generated {@link IExpandedFilesConfig.dest} paths.
@@ -622,17 +622,21 @@ declare module grunt {
              * and this function must return a new dest value.
              * If the same dest is returned more than once, each src which used it will be added to an array of sources for it.
              */
-            rename?: boolean
+            rename?: Function
         }
 
         /**
-         * @see {@link http://gruntjs.com/configuring-tasks#files-object-format}
+         * @see {@link http://gruntjs.com/configuring-tasks#files-array-format}
          */
-        interface IFilesMap {
+        interface IFileMap {
             /**
-             * A map of sources to a destination.
+             * source filenames.
              */
-            [dest: string]: string[]
+            src: string[]
+            /**
+             * destination filename.
+             */
+            dest: string
         }
     }
 
@@ -804,7 +808,7 @@ declare module grunt {
              * Normalizes a task target configuration object into an array of src-dest file mappings.
              * This method is used internally by the multi task system this.files / grunt.task.current.files property.
              */
-            normalizeMultiTaskFiles(data: grunt.config.IProjectConfig, targetname?: string): grunt.file.IFilesMap
+            normalizeMultiTaskFiles(data: grunt.config.IProjectConfig, targetname?: string): Array<grunt.file.IFileMap>
         }
 
         interface AsyncResultCatcher {