Reorder eager extension activation

[joyceerhl]

For #171135

In local testing (launch VS Code then open Developer: Startup Performance this exhibits a mild reduction in the time to code/didStartWorkbench. I'd like to get some additional validation in insiders for whether this makes a difference e.g. with the perf bot.

[alexdima]

I like this idea very much. But here's a different way to tackle it:

• the extension host receives startup related activation requests via AbstractExtHostExtensionService.$activateByEvent
• from debugging this locally, all file system activation events are already received there, they're all just waiting on the readyToRunExtensions barrier
• we could open the barrier and then wait for all activation events to finish and only then do the eager activation events (*, workspaceContains, etc).
• this would allow to avoid having a special case for filesystems, and it would work for all kinds of startup related activation events.
• we should test this, I only tried it locally, not on the web.

Here's a change that could be applied on main to get what I describe:

diff --git a/src/vs/workbench/api/common/extHostExtensionActivator.ts b/src/vs/workbench/api/common/extHostExtensionActivator.ts
index 47f20ca08dd..26c8795aaa6 100644
--- a/src/vs/workbench/api/common/extHostExtensionActivator.ts
+++ b/src/vs/workbench/api/common/extHostExtensionActivator.ts
@@ -193,6 +193,14 @@ export class ExtensionsActivator implements IDisposable {
 		}
 	}
 
+	public async waitForActivatingExtensions(): Promise<void> {
+		const res: Promise<boolean>[] = [];
+		for (const [_, op] of this._operations) {
+			res.push(op.wait());
+		}
+		await Promise.all(res);
+	}
+
 	public isActivated(extensionId: ExtensionIdentifier): boolean {
 		const op = this._operations.get(extensionId);
 		return Boolean(op && op.value);
diff --git a/src/vs/workbench/api/common/extHostExtensionService.ts b/src/vs/workbench/api/common/extHostExtensionService.ts
index 0b0dba8355b..afe2939e5b8 100644
--- a/src/vs/workbench/api/common/extHostExtensionService.ts
+++ b/src/vs/workbench/api/common/extHostExtensionService.ts
@@ -756,6 +756,10 @@ export abstract class AbstractExtHostExtensionService extends Disposable impleme
 
 		return this._readyToStartExtensionHost.wait()
 			.then(() => this._readyToRunExtensions.open())
+			.then(() => {
+				// wait for all activation events that came in during workbench startup, but at maximum 1s
+				return Promise.race([this._activator.waitForActivatingExtensions(), timeout(1000)]);
+			})
 			.then(() => this._handleEagerExtensions())
 			.then(() => {
 				this._eagerExtensionsActivated.open();

[joyceerhl]

@alexdima I just tried this out https://insiders.vscode.dev/github/microsoft/vscode?vscode-version=9402aef94bbb84354fe22b3455a13750be79e3f5 and it seems to work well in web and remote. Thank you for the pointer!