Complete exported macros in #[macro_use($0)]

[unexge]

Closes #15657.

Originally added a test case for incomplete input:

#[test]
fn completes_incomplete_syntax() {
    check(
        r#"
//- /dep.rs crate:dep
#[macro_export]
macro_rules! foo {
    () => {};
}

//- /main.rs crate:main deps:dep
#[macro_use($0
extern crate dep;
"#,
        expect![[r#"
                ma foo
            "#]],
    )
}

but couldn't make it pass and removed it 😅 Our current recovering logic doesn't work for token trees and for this code:

#[macro_use(
extern crate lazy_static;

fn main() {}

we ended up with this syntax tree:

SOURCE_FILE@0..53
  ATTR@0..52
    POUND@0..1 "#"
    L_BRACK@1..2 "["
    META@2..52
      PATH@2..11
        PATH_SEGMENT@2..11
          NAME_REF@2..11
            IDENT@2..11 "macro_use"
      TOKEN_TREE@11..52
        L_PAREN@11..12 "("
        WHITESPACE@12..13 "\n"
        EXTERN_KW@13..19 "extern"
        WHITESPACE@19..20 " "
        CRATE_KW@20..25 "crate"
        WHITESPACE@25..26 " "
        IDENT@26..37 "lazy_static"
        SEMICOLON@37..38 ";"
        WHITESPACE@38..40 "\n\n"
        FN_KW@40..42 "fn"
        WHITESPACE@42..43 " "
        IDENT@43..47 "main"
        TOKEN_TREE@47..49
          L_PAREN@47..48 "("
          R_PAREN@48..49 ")"
        WHITESPACE@49..50 " "
        TOKEN_TREE@50..52
          L_CURLY@50..51 "{"
          R_CURLY@51..52 "}"
  WHITESPACE@52..53 "\n"

Maybe we can try to parse the token tree in crates/ide-completion/src/context/analysis.rs but I'm not sure what's the best way forward.

[Veykril]

Fine to do now, but ideally this would be done the same way we handle derives, by giving macro_use a dummy expansion we can map into. #11929

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 3b8801c has been approved by Veykril

It is now in the queue for this repository.

[Veykril]

Our current recovering logic doesn't work for token trees

There is not much we can do there, since a token tree ends at its closing delimiter.

[bors]

⌛ Testing commit 3b8801c with merge 23a1280...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 23a1280 to master...