Performance regression in errorOnImplicitAnyModule

[dtinth]

TypeScript Version: 3.0.1

Search Terms:
typesPackageExists
Performance slow
tsserver
vscode typescript slow

Description
Since TypeScript 3.0, I find the TypeScript language server is slowing down noticeably. I ran VS Code with TSS_DEBUG=8283 code . to profile where the performance bottleneck is.

Most of the time is spent in findReferences function (and its descendant). I am using “Reference CodeLens” which I believe to have caused this command to be executed often.

Looking at the “heavy” graph, tsserver spends most of its time in the typesPackageExists function.

Looking at the performance chart, findReferences called typesPackageExists multiple times.

The function typesPackageExists appeared in commit 2b9166b:

https://github.com/Microsoft/TypeScript/blob/937afab4b026c9ed527c8369275c749fc8f2af99/src/compiler/checker.ts#L2261-L2264

        function typesPackageExists(packageName: string): boolean {
            return host.getSourceFiles().some(sf => !!sf.resolvedModules && !!forEachEntry(sf.resolvedModules, r =>
                r && r.packageId && r.packageId.name === getTypesPackageName(packageName)));
        }

I set up a breakpoint here:

This allows me to see how many source files I have:

Therefore, tsserver in VS Code slows down when both conditions are met:

• References CodeLens is enabled. (Confirmed: Disabling javascript.referencesCodeLens.enabled and typescript.referencesCodeLens.enabled fixed this issue.)
• The project is large.

[dtinth]

Thanks! :)