fix: only have the stream close after writing Webpack filesystem caches

index.js

@@ -190,12 +190,28 @@ module.exports = function (options, wp, done) {
         }
         self.emit('compilation-error', compilationError);
       }
-      if (!isInWatchMode) {
-        self.queue(null);
-      }
-      done(err, stats);
-      if (isInWatchMode && !isSilent) {
-        fancyLog('webpack is watching for changes');
+      if (isInWatchMode) {
+        done(err, stats);
+        if (!isSilent) {
+          fancyLog('webpack is watching for changes');
+        }
+      } else {
+        function closeStream() {
+          self.queue(null);
+          done(err, stats);
+        }
+
+        if (compiler.close) {
+          // For Webpack v5 and above:
+          // From https://webpack.js.org/api/node/#run: we need to close
+          // the compiler so that low-priority (e.g., caching) work happens
+          compiler.close(closeStream);
+        } else {
+          // Webpack v4 doesn't have compiler.close, so just immediately end
+          // the stream
+          // (see https://github.com/webpack/webpack/blob/v4.0.0/lib/Compiler.js)
+          closeStream();
+        }
       }
     };
 

test/test.js

@@ -3,6 +3,7 @@ const webpack = require('../');
 const path = require('path');
 const fs = require('vinyl-fs');
 const named = require('vinyl-named');
+const nodeFS = require('fs');
 
 const base = path.resolve(__dirname, 'fixtures');
 
@@ -93,7 +94,7 @@ test('stream multiple entry points', function (t) {
 test('empty input stream', function (t) {
   t.plan(1);
 
-  const entry = fs.src('test/path/to/nothing', { allowEmpty: true });
+  const entry = fs.src('test/path/to/nothing', {allowEmpty: true});
   const stream = webpack({
     config: {},
     quiet: true
@@ -199,3 +200,32 @@ test('error formatting', function (t) {
   });
   entry.pipe(stream);
 });
+
+test('writes filesystem cache files', function (t) {
+  t.plan(2);
+  const entry = fs.src('test/fixtures/entry.js');
+  const cacheDirectory = path.join(__dirname, 'testCache');
+
+  nodeFS.rmdirSync(cacheDirectory, {recursive: true, force: true});
+  t.equal(nodeFS.existsSync(cacheDirectory), false, 'cache directory should not exist at start');
+
+  const stream = webpack({
+    config: {
+      mode: 'development',
+      output: {filename: 'bundle.js'},
+      cache: {
+        type: 'filesystem',
+        idleTimeoutForInitialStore: 0,
+        cacheDirectory
+      },
+    },
+    quiet: true
+  });
+
+  stream.on('end', function () {
+    t.equal(nodeFS.existsSync(cacheDirectory), true, 'should have created a cache directory after compile');
+    nodeFS.rmdirSync(cacheDirectory, {recursive: true, force: true});
+  });
+
+  entry.pipe(stream);
+});