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Rollup merge of #128229 - tdittr:unsafe-extern-abi-error, r=compiler-errors

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Improve `extern "<abi>" unsafe fn()` error message

These errors were already reported in #87217, and fixed by #87235 but missed the case of an explicit ABI.

This PR does not cover multiple keywords like `extern "C" pub const unsafe fn()`, but I don't know what a good way to cover this  would be. It also seems rarer than `extern "C" unsafe` which I saw happen a few times in workshops.
This commit is contained in:
Trevor Gross 2024-07-26 19:03:08 -04:00 • committed by GitHub
commit 7eaf74743b
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5 changed files with 47 additions and 11 deletions
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9
compiler/rustc_parse/src/parser/item.rs
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@ -2483,12 +2483,15 @@ impl<'a> Parser<'a> {
/// `check_pub` adds additional `pub` to the checks in case users place it
/// wrongly, can be used to ensure `pub` never comes after `default`.
pub(super) fn check_fn_front_matter(&mut self, check_pub: bool, case: Case) -> bool {
const ALL_QUALS: &[Symbol] =
&[kw::Pub, kw::Gen, kw::Const, kw::Async, kw::Unsafe, kw::Safe, kw::Extern];
// We use an over-approximation here.
// `const const`, `fn const` won't parse, but we're not stepping over other syntax either.
// `pub` is added in case users got confused with the ordering like `async pub fn`,
// only if it wasn't preceded by `default` as `default pub` is invalid.
let quals: &[Symbol] = if check_pub {
&[kw::Pub, kw::Gen, kw::Const, kw::Async, kw::Unsafe, kw::Safe, kw::Extern]
ALL_QUALS
} else {
&[kw::Gen, kw::Const, kw::Async, kw::Unsafe, kw::Safe, kw::Extern]
};
@ -2518,9 +2521,9 @@ impl<'a> Parser<'a> {
|| self.check_keyword_case(kw::Extern, case)
&& self.look_ahead(1, |t| t.can_begin_string_literal())
&& (self.look_ahead(2, |t| t.is_keyword_case(kw::Fn, case)) ||
// this branch is only for better diagnostic in later, `pub` is not allowed here
// this branch is only for better diagnostics; `pub`, `unsafe`, etc. are not allowed here
(self.may_recover()
&& self.look_ahead(2, |t| t.is_keyword(kw::Pub))
&& self.look_ahead(2, |t| ALL_QUALS.iter().any(|&kw| t.is_keyword(kw)))
&& self.look_ahead(3, |t| t.is_keyword_case(kw::Fn, case))))
}