Do not suggest importing inaccessible items

[FabianWolff]

Fixes #88472. For this example:

mod a {
    struct Foo;
}

mod b {
    type Bar = Foo;
}

rustc currently emits:

error[E0412]: cannot find type `Foo` in this scope
 --> test.rs:6:16
  |
6 |     type Bar = Foo;
  |                ^^^ not found in this scope
  |
help: consider importing this struct
  |
6 |     use a::Foo;
  |

this is incorrect, as applying this suggestion leads to

error[E0603]: struct `Foo` is private
 --> test.rs:6:12
  |
6 |     use a::Foo;
  |            ^^^ private struct
  |
note: the struct `Foo` is defined here
 --> test.rs:2:5
  |
2 |     struct Foo;
  |     ^^^^^^^^^^^

With my changes, I get:

error[E0412]: cannot find type `Foo` in this scope
 --> test.rs:6:16
  |
6 |     type Bar = Foo;
  |                ^^^ not found in this scope
  |
  = note: this struct exists but is inaccessible:
          a::Foo

As for the wildcard mentioned in #88472, I would argue that the warning is actually correct, since the import is unused. I think the real issue is the wrong suggestion, which I have fixed here.

[rust-highfive]

r? @michaelwoerister

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[michaelwoerister]

r? @JohnTitor (randomly picked someone from wg-diagnostics, feel free to re-assign)

[JohnTitor]

Seems good but I'm not part of t-compiler, r? @estebank could you take a look?

[estebank]

I think the changes are an improvement already, but I have a few ideas on how we could improve them further. I'm r=me for the code changes as they are, but I would like to continue tweaking them so the output is nicer. Would you have time to make them perfect, @FabianWolff?

[FabianWolff]

I think the changes are an improvement already, but I have a few ideas on how we could improve them further. I'm r=me for the code changes as they are, but I would like to continue tweaking them so the output is nicer. Would you have time to make them perfect, @FabianWolff?

Thanks for the review! Yes, I'll try to implement your suggestions (though I won't get around to it today).

[bors]

☔ The latest upstream changes (presumably #89037) made this pull request unmergeable. Please resolve the merge conflicts.

[estebank]

One last thing: if the DefId belongs to the local crate, we should maybe suggest making the item (and all its parents, if applicable) pub? Anyone experienced will not need it and figure things out just with even the current message in this PR, but I could envision anyone just starting asking themselves "ok, so what do I do? how do I make it accessible?". Of course, that is not necessarily needed for this PR, but we don't address it, could you file a follow up ticket to do that?

[FabianWolff]

@estebank I have now implemented your suggestions! I did not get around to your proposal in #88838 (comment); instead, I have opened #89057 as a follow-up, as you have suggested (I might come back to it if I have time in the next few days).

[bors]

☔ The latest upstream changes (presumably #89262) made this pull request unmergeable. Please resolve the merge conflicts.

[estebank]

r=me after rebasing

[crlf0710]

I'm curious whether this will fix #88636 too

[estebank]

@crlf0710 it's very likely it will, good catch!

[FabianWolff]

@estebank Rebased & ready.

[estebank]

@bors r+

[bors]

📌 Commit 750018e has been approved by estebank

[bors]

⌛ Testing commit 750018e with merge 93468f041e3a0ab409c395d2cbf7a790e4c8ff8c...

[bors]

💥 Test timed out

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[estebank]

@bors retry