Allow multiple tsconfig configurations for `--project` flag in cli

[michal-minich]

Suggestion

🔍 Search Terms

is:open project multiple label:Suggestion

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion / 📃 Motivating Example

allow tsc to be invoked with multiple project configuration with --project / -p flag in cli like:

tsc --project tsconfig.dev.json tsconfig.prod.json

alternative syntax:
tsc --project tsconfig.dev.json --project tsconfig.prod.json

currently it is only possible to have 1 configuration per tsc run, so tsc has to be executed for each tsconfig like:

tsc --project tsconfig.dev.json 
tsc --project tsconfig.prod.json

Note --build / -b flag allows specify multiple projects already.

💻 Use Cases

This is useful when one projects has more target configurations (e.g. for deployments / testing / user agents / devices).
This is performance optimization only. The end result is already achievable by ruining tsc multiple times.

[MartinJohns]

Somewhat related: #37884

This is performance optimization only.

I doubt this brings any performance, unless it internally re-uses some data structures across the project, which likely would be a massive undertaking.

[RyanCavanaugh]

Apart from pure startup time, there's not anything meaningful that can be reused between two subsequent project builds. It might actually be worse from a total time perspective because of memory pressure/fragmentation.

"Merging" config files on the command line (as linked) is something that I think is still on the table as a feature, so providing some syntax to do multiple projects today just for convenience would muddy the waters in a way that I think doesn't really pay for itself in terms of added value.

If you want to run multiple projects on a single command execution, you can use tsc --build with "solution" tsconfig files.

[michal-minich]

OK, I understand. Unfortunately with --build all files needs to be included with glob pattern to be "root", as only these are checked for modifications. The -p flag has ability to specify only the "main.ts" file and let tsc identify which files should be actually compiled to the output.

[typescript-bot]

This issue has been marked as "Declined" and has seen no recent activity. It has been automatically closed for house-keeping purposes.