[pickers] Avoid some nested imports in @mui/utils

[alexfauquette]

Fix #9170

[mui-bot]

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These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	612.9	1,200.4	612.9	858.04	246.262
Sort 100k rows	ms	547.4	1,184.9	1,184.9	956.86	215.614
Select 100k rows	ms	239.3	398.4	282.8	311.14	63.932
Deselect 100k rows	ms	204.9	287.4	207.6	227.38	31.673

Generated by 🚫 dangerJS against 8dcf956

[flaviendelangle]

Are we sure we want to do this?
For me it's going against what we are trying to achieve in mui/material-ui#35840

[alexfauquette]

Are we sure we want to do this?

Not at all, that's why I asked for your review 😉
But in that case, I've no clue about how to solve the issue

[flaviendelangle]

I think the issue is that @mui/utils nested imports are files, not folders.
So the build process can not create nested package.json, which causes the issue here:

vs

So for me, the clean fix would be to move all the utils (or at least the one used in other packages) into folders with an index file.
@michaldudak I'd like your opinion here. On the core repo, all the imports from @mui/utils are from the root, but mui/material-ui#35840 lets me think that's not something we want to keep in the future. Does my proposal make sense?

[michaldudak]

I share @flaviendelangle's concerns about not using nested imports (especially when we try to teach other developers to use them). If introducing directories solves the problem, we can do it. In the future, we can explicitly say it's a private package, then reorganize it a bit more (e.g., place all the prop-types utilities into one directory etc.).

[flaviendelangle]

@michaldudak @alexfauquette @LukasTy

If I open a PR tomorrow on the core to create the folders, I think we can fix the problem without having the intermediate step proposed in this PR.
But if one of you think the fix will take more that 2-3 weeks top, then I think the intermediate step is needed to unlock our users.

[LukasTy]

But if one of you think the fix will take more that 2-3 weeks top, then I think the intermediate step is needed to unlock our users.

This PR has already been open for 2 weeks already. 🙈
What's 1 or 2 more weeks if it comes to that? 🤷

[flaviendelangle]

Here is the PR: mui/material-ui#37586
I migrated all the files that are used in the X repo