Plan item #41678 enable @ts-check

[Erich Gamma (egamma)]

No description provided.

[João Moreno (joaomoreno)]

Erich Gamma (@egamma) As Travis and AppVeyor complain, there's a problem with this. The build folder fails to build:

> code-oss-dev-build@1.0.0 compile /Users/joao/Work/vscode/build
> tsc
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/dependencies.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.editor.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.extensions.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.hygiene.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.mixin.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.test.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.vscode.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.vscode.linux.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/gulpfile.vscode.win32.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/lib/builtInExtensions.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/lib/electron.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/lib/watch/index.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/lib/watch/watch-nsfw.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/lib/watch/watch-win32.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/npm/postinstall.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/npm/preinstall.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/npm/update-all-grammars.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/npm/update-grammar.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/build/npm/update-theme.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/src/buildfile.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/src/vs/code/buildfile.js' because it would overwrite input file.
error TS5055: Cannot write file '/Users/joao/Work/vscode/src/vs/workbench/buildfile.js' because it would overwrite input file.

[João Moreno (joaomoreno)]

Erich Gamma (@egamma) Also... how exactly does src/buildfile.js get checked? It doesn't have a @ts-check marker nor does its corresponding tsconfig.json have checkJS...

[Erich Gamma (egamma)]

Erich Gamma (@egamma) As Travis and AppVeyor complain, there's a problem with this. The build folder fails to build:

The issue is that when you enable allowJS in the tsconfig.json, then TypeScript will transpile the JS files. I need to find a way to specifc --noEmit for the .js files.

[Erich Gamma (egamma)]

Erich Gamma (@egamma) Also... how exactly does src/buildfile.js get checked? It doesn't have a ts-check (@ts-check) marker nor does its corresponding tsconfig.json have checkJS...

I was surprised as well, but the TS type checker reaches it also when running tsc --noEmit from the build folder. So I assume there is a dependency from a source file in the build folder to src/buildfile.js.

[João Moreno (joaomoreno)]

You're right!

https://github.com/Microsoft/vscode/blob/master/build/gulpfile.vscode.js#L25

[Erich Gamma (egamma)]

Here is the issue, when you want to enable checkJS in the tsconfig.json then you also must enable allowJS. Now, when you enable allowJS then TypeScript will compile and emit output for .js files (useful when you want to downlevel compile JS).

I see different options:

1. add ts-check (@ts-check) to all the .js files we want to have type checked. Downside is that we must remember to add the comment to the .js files. Also it is not clear to me how I can configure the parameters you would configure in the tsconfig.json.

2. Add the setting "javascript.implicitProjectConfig.checkJs": true as a workspace setting. It seems that this doesn´t affect compilation, but adds many more files to the language server and this might slow down things. Same as for 1. is not clear where you configure the parameters for typescript in this case.

3. Add two tsconfig.json files to the build folder. One is used by the language service and will be used for checking, one will be used for compiling the project during the build.

I´ll add option 2) to the PR for testing.

[Erich Gamma (egamma)]

Hmm, .js files are still compiled so option 2 is not an option...

[Erich Gamma (egamma)]

I´ve looked into options 2) and 3). The issue with these options is that the project of the tsconfig.json in the build folder is ignored. This means some typings are not retrieved from the build folder but from the global typings cache. The version of a global typing can differ from the one inside the build folders. This means you get different error messages from Typescript. You can work around them by adding reference path comments that point to the typings in the build folder.

/// <reference path='lib/typings/event-stream.d.ts'/>

Such comments are a pain to maintain and duplicates the project context from the tsconfig.json.

My conclusion is that the checkJS must use the project context defined by tsconfig.json and that Typescript should support that you can enable checkJS without having to enable allowJS. Filed issue microsoft/TypeScript#21435.

[Erich Gamma (egamma)]

João Moreno (@joaomoreno) closing in favor of #42731 (this one is messy and mixes different experiments).