Autocompletion is working in TS 4.7 to 4.9 but broken/gone in TS 5

[jgoux]

Bug Report

🔎 Search Terms

autocompletion

🕗 Version & Regression Information

• This changed between versions ^4.7.0 and ^5
• I was unable to test this on prior versions because some type features such as string literal manipulation are not available before 4.7

⏯ Playground Link

Playground link with relevant code

💻 Code

Please go to the end of the code and try the defineConfig function:

defineConfig({
  exclude: {
    data: ["<cursor here, ctrl+space>"],
    structure: {
      schemas: ["secret", "<cursor here, ctrl+space>"],
      tables: ["<cursor here, ctrl+space>"]
    }
  }
})

🙁 Actual behavior

Between TS 4.7 and 4.9, we have autocompletion available for all array values under the exclude key
At TS 5 and above (I tried nightly as well), the autocompletion is gone

🙂 Expected behavior

The autocompletion should work the same as with TS 4.7 and 4.9

[Andarist]

Could you specify what exact completions you expect at given positions? I'm guessing that string completions are broken here (although some work in extensions). On top of that, I can see some inconsistencies between string completions and regular ones (in 4.9 as well)

[Andarist]

This was broken by this PR of mine although I've hoped to fix its regressions with #52875 . Gonna have to investigate what is different about this one here.

[jgoux]

@Andarist As exclude.data, exclude.structure.schemas and exclude.structure.tables are the generics I need to pick up, when the array is empty it's typed as never[] | undefined, so the normal autocompletion is not working in both 4.9 and 5 (I think there is no way I can make it works, or I'm too dumb to figure it out 😄).
But if I use quotes in those like "<cursor here, ctrl+space>" it works in 4.9 but not in 5.
What's even stranger is that in 5, if you do ""<cursor here, ctrl+space> (so the cursor after the empty quotes) it will provide autocompletion.

Edit: It seems like introducing an item that isn't part of the expected union switch the type of the array to the union itself so the autocompletion works:

The empty string being "wrong", works in both 4.9 and 5:

The only difference between 4.9 and 5 then it's that the suggestions are showing when the cursor is between the quotes ["<cursor, ctrl+space>"], but not anymore in 5.