Added --preserveWatchOutput flag

[JoshuaKGoldberg]

Description: "Whether to keep outdated console output in watch mode instead of clearing the screen."
Since the pretty? compiler options flag is marked as @internal, made this one too.

Fixes #21295. Sending a PR before the issue is approved to increase probability of this shipping the same time as the clearing feature.

[gcnew]

Maybe it would be better if the screen clearing was behind a flag. This way the new option would be a pure addition with the current behaviour unaltered.

[JoshuaKGoldberg]

@gcnew Ehh, I really like the new behavior. It's quite useful on large projects. The lack of complaints from insiders makes me (without any experience tracking these things) suspect it wouldn't be too bad.

[imhoffd]

I like the new behavior by default as well, but tsc -w becomes totally unusable when multiple compilers are run concurrently (think monorepos).

@mhegazy You mentioned that you don't want to add new flags (#21295 (comment)). Perhaps if could be generalized to a single flag which disables all tty view manipulation now and in the future. Even more generalized to disable any sort of interactivity. For yarn, this is --non-interactive. For TS, possibly --noInteractive?

If the ability to disable this feature isn't added, I (and others) will need to write a thin wrapper to tsc which tosses out the control character now being spit into our terminals.

[roblav96]

#21295 (comment) by @clarkdave posted a working fix

[TimonVS]

@JoshuaKGoldberg Why did you close the PR? The fix mentioned by @roblav96 doesn't work for Mac users (I don't want to force everyone in my team to install gsed).

[JoshuaKGoldberg]

I closed the PR because a core TS member (mhegazy) mentioned last month that they don't want to add a compiler option for this, and since then it's obtained a few merge conflicts. You're welcome to send a new one & try to push for it though!

[JoshuaKGoldberg]

On second thought, @mhegazy, what are your thoughts on switching this flag to be opt-in? It sounds like this change broke a lot of people (sorry folks!).

I'll resolve the merge conflicts today regardless.

[JoshuaKGoldberg]

I've sent a second PR, #22248, that has the equivalent change to make the behavior opt-in with a new --clearWatchOutput` flag. IMO that's a better fix.

[JoshuaKGoldberg]

15:55:53   59310 passing (2m)
15:55:53   1 failing
15:55:53 
15:55:53   1) conformance tests
15:55:53        conformance tests for tests/cases/conformance/types/uniqueSymbol/uniqueSymbolsErrors.ts
15:55:53          Correct errors for tests/cases/conformance/types/uniqueSymbol/uniqueSymbolsErrors.ts:
15:55:53      Error: The baseline file uniqueSymbolsErrors.errors.txt has changed.

Does not show up locally and does not relate to this change. Unrelated?

[mhegazy]

thanks!