Do not drop aggregated changes with resumed compilation

lib/Watching.js

@@ -297,14 +297,21 @@ class Watching {
 			return;
 		}
 		if (this.watcher) {
-			this.compiler.modifiedFiles =
-				this.watcher.getAggregatedChanges &&
-				this.watcher.getAggregatedChanges();
-			this.compiler.removedFiles =
-				this.watcher.getAggregatedRemovals &&
-				this.watcher.getAggregatedRemovals();
-			this.compiler.fileTimestamps = this.watcher.getFileTimeInfoEntries();
-			this.compiler.contextTimestamps = this.watcher.getContextTimeInfoEntries();
+			// Following must be either removed or merged
+			//   because it will overwrite existing (and unprocessed):
+			//   - this.compiler.modifiedFiles
+			//   - this.compiler.removedFiles
+			// Alternatively, we can merge those with values from the
+			//   oldWatcher in NodeWatchFileSystem
+
+			// this.compiler.modifiedFiles =
+			// 	this.watcher.getAggregatedChanges &&
+			// 	this.watcher.getAggregatedChanges();
+			// this.compiler.removedFiles =
+			// 	this.watcher.getAggregatedRemovals &&
+			// 	this.watcher.getAggregatedRemovals();
+			// this.compiler.fileTimestamps = this.watcher.getFileTimeInfoEntries();
+			// this.compiler.contextTimestamps = this.watcher.getContextTimeInfoEntries();
 			this.pausedWatcher = this.watcher;
 			this.watcher.pause();
 			this.watcher = null;

lib/node/NodeWatchFileSystem.js

@@ -84,6 +84,16 @@ class NodeWatchFileSystem {
 		this.watcher.watch({ files, directories, missing, startTime });
 
 		if (oldWatcher) {
+			// Ideally we need it in watchpack, e.g.:
+			//   oldWatcher.close({ emitAggregated: true })
+			// (this will emit aggregated values before closing)
+			// Dirty workaround that does the same:
+			if (
+				oldWatcher.aggregatedChanges.size > 0 ||
+				oldWatcher.aggregatedRemovals.size > 0
+			) {
+				oldWatcher._onTimeout();
+			}
 			oldWatcher.close();
 		}
 		return {

test/WatchSuspend.test.js

@@ -45,6 +45,7 @@ describe("WatchSuspend", () => {
 				}
 			});
 			watching = compiler.watch({ aggregateTimeout: 50 }, () => {});
+
 			compiler.hooks.done.tap("WatchSuspendTest", () => {
 				if (onChange) onChange();
 			});
@@ -92,5 +93,28 @@ describe("WatchSuspend", () => {
 			};
 			watching.resume();
 		});
+
+		it("should not ignore changes during resumed compilation", async () => {
+			// aggregateTimeout must be long enough for this test
+			//  So set-up new watcher and wait when initial compilation is done
+			await new Promise(resolve => {
+				watching.close();
+				watching = compiler.watch({ aggregateTimeout: 1000 }, resolve);
+			});
+			return new Promise(resolve => {
+				watching.suspend();
+				fs.writeFileSync(filePath, "'baz'", "utf-8");
+
+				// Run resume between "changed" and "aggregated" events
+				setTimeout(() => {
+					watching.resume();
+
+					setTimeout(() => {
+						expect(fs.readFileSync(outputPath, "utf-8")).toContain("'baz'");
+						resolve();
+					}, 2000);
+				}, 200);
+			});
+		});
 	});
 });