when capping decoration events pick somewhat smarter,...

when capping decoration events pick somewhat smarter, https://github.com/microsoft/vscode/issues/108292

src/vs/base/common/strings.ts

@@ -55,6 +55,20 @@ export function escapeRegExpCharacters(value: string): string {
 	return value.replace(/[\\\{\}\*\+\?\|\^\$\.\[\]\(\)]/g, '\\$&');
 }
 
+/**
+ * Counts how often `character` occurs inside `value`.
+ */
+export function count(value: string, character: string): number {
+	let result = 0;
+	const ch = character.charCodeAt(0);
+	for (let i = value.length - 1; i >= 0; i--) {
+		if (value.charCodeAt(i) === ch) {
+			result++;
+		}
+	}
+	return result;
+}
+
 /**
  * Removes all occurrences of needle from the beginning and end of haystack.
  * @param haystack string to trim

src/vs/workbench/api/common/extHostDecorations.ts

@@ -12,7 +12,9 @@ import { ExtensionIdentifier } from 'vs/platform/extensions/common/extensions';
 import { createDecorator } from 'vs/platform/instantiation/common/instantiation';
 import { IExtHostRpcService } from 'vs/workbench/api/common/extHostRpcService';
 import { ILogService } from 'vs/platform/log/common/log';
-import { asArray } from 'vs/base/common/arrays';
+import { asArray, groupBy } from 'vs/base/common/arrays';
+import { count } from 'vs/base/common/strings';
+import { dirname } from 'vs/base/common/path';
 
 interface ProviderData {
 	provider: vscode.FileDecorationProvider;
@@ -22,6 +24,7 @@ interface ProviderData {
 export class ExtHostDecorations implements ExtHostDecorationsShape {
 
 	private static _handlePool = 0;
+	private static _maxEventSize = 250;
 
 	readonly _serviceBrand: undefined;
 	private readonly _provider = new Map<number, ProviderData>();
@@ -40,9 +43,34 @@ export class ExtHostDecorations implements ExtHostDecorationsShape {
 		this._proxy.$registerDecorationProvider(handle, extensionId.value);
 
 		const listener = provider.onDidChange(e => {
-			this._proxy.$onDidChange(handle, !e || (Array.isArray(e) && e.length > 250)
-				? null
-				: asArray(e));
+			if (!e) {
+				this._proxy.$onDidChange(handle, null);
+				return;
+			}
+			let array = asArray(e);
+			if (array.length <= ExtHostDecorations._maxEventSize) {
+				this._proxy.$onDidChange(handle, array);
+				return;
+			}
+
+			// too many resources per event. pick one resource per folder, starting
+			// with parent folders
+			const mapped = array.map(uri => ({ uri, rank: count(uri.path, '/') }));
+			const groups = groupBy(mapped, (a, b) => a.rank - b.rank);
+			let picked: URI[] = [];
+			outer: for (let uris of groups) {
+				let lastDirname: string | undefined;
+				for (let obj of uris) {
+					let myDirname = dirname(obj.uri.path);
+					if (lastDirname !== myDirname) {
+						lastDirname = myDirname;
+						if (picked.push(obj.uri) >= ExtHostDecorations._maxEventSize) {
+							break outer;
+						}
+					}
+				}
+			}
+			this._proxy.$onDidChange(handle, picked);
 		});
 
 		return new Disposable(() => {