Add setting to control use of -d flag by the formatting tool

package.json

@@ -296,6 +296,11 @@
           "default": [],
           "description": "Flags to pass to format tool (e.g. ['-s'])"
         },
+        "go.useDiffForFormatting": {
+          "type": "boolean",
+          "default": true,
+          "description": "Run the formatting tools with the -d flag"
+        },
         "go.useCodeSnippetsOnFunctionSuggest": {
           "type": "boolean",
           "default": false,

src/goFormat.ts

@@ -28,7 +28,7 @@ export class Formatter {
 
 			let formatCommandBinPath = getBinPath(this.formatCommand);
 			let formatFlags = vscode.workspace.getConfiguration('go')['formatFlags'] || [];
-			let canFormatToolUseDiff = isDiffToolAvailable();
+			let canFormatToolUseDiff = vscode.workspace.getConfiguration('go')['useDiffForFormatting'] && isDiffToolAvailable();
 			if (canFormatToolUseDiff) {
 				formatFlags.push('-d');
 			}