Delete output folder before building

extensions/ql-vscode/gulpfile.ts/index.ts

@@ -1,15 +1,18 @@
 import * as gulp from 'gulp';
-import { compileTypeScript, watchTypeScript, copyViewCss } from './typescript';
+import { compileTypeScript, watchTypeScript, copyViewCss, cleanOutput } from './typescript';
 import { compileTextMateGrammar } from './textmate';
 import { copyTestData } from './tests';
 import { compileView } from './webpack';
 import { packageExtension } from './package';
 import { injectAppInsightsKey } from './appInsights';
 
 export const buildWithoutPackage =
-  gulp.parallel(
-    compileTypeScript, compileTextMateGrammar, compileView, copyTestData, copyViewCss
+  gulp.series(
+    cleanOutput,
+    gulp.parallel(
+      compileTypeScript, compileTextMateGrammar, compileView, copyTestData, copyViewCss
+    )
   );
 
-export { compileTextMateGrammar, watchTypeScript, compileTypeScript, copyTestData, injectAppInsightsKey };
+export { cleanOutput, compileTextMateGrammar, watchTypeScript, compileTypeScript, copyTestData, injectAppInsightsKey };
 export default gulp.series(buildWithoutPackage, injectAppInsightsKey, packageExtension);

extensions/ql-vscode/gulpfile.ts/typescript.ts

@@ -2,6 +2,7 @@ import * as colors from 'ansi-colors';
 import * as gulp from 'gulp';
 import * as sourcemaps from 'gulp-sourcemaps';
 import * as ts from 'gulp-typescript';
+import * as del from 'del';
 
 function goodReporter(): ts.reporter.Reporter {
   return {
@@ -20,6 +21,10 @@ function goodReporter(): ts.reporter.Reporter {
 
 const tsProject = ts.createProject('tsconfig.json');
 
+export function cleanOutput() {
+  return tsProject.projectDirectory ? del(tsProject.projectDirectory + '/out/*') : Promise.resolve();
+}
+
 export function compileTypeScript() {
   return tsProject.src()
     .pipe(sourcemaps.init())

extensions/ql-vscode/package.json

@@ -1016,6 +1016,7 @@
     "@types/chai-as-promised": "~7.1.2",
     "@types/child-process-promise": "^2.2.1",
     "@types/classnames": "~2.2.9",
+    "@types/del": "^4.0.0",
     "@types/fs-extra": "^9.0.6",
     "@types/glob": "^7.1.1",
     "@types/google-protobuf": "^3.2.7",
@@ -1049,6 +1050,7 @@
     "chai": "^4.2.0",
     "chai-as-promised": "~7.1.1",
     "css-loader": "~3.1.0",
+    "del": "^6.0.0",
     "eslint": "~6.8.0",
     "eslint-plugin-react": "~7.19.0",
     "glob": "^7.1.4",