Rollup merge of #138842 - Noratrieb:inline-exported, r=me,saethlin

Emit `unused_attributes` for `#[inline]` on exported functions

I saw someone post a code sample that contained these two attributes, which immediately made me suspicious.
My suspicions were confirmed when I did a small test and checked the compiler source code to confirm that in these cases, `#[inline]` is indeed ignored (because you can't exactly `LocalCopy`an unmangled symbol since that would lead to duplicate symbols, and doing a mix of an unmangled `GloballyShared` and mangled `LocalCopy` instantiation is too complicated for our current instatiation mode logic, which I don't want to change right now).

So instead, emit the usual unused attribute lint with a message saying that the attribute is ignored in this position.

I think this is not 100% true, since I expect LLVM `inlinehint` to still be applied to such a function, but that's not why people use this attribute, they use it for the `LocalCopy` instantiation mode, where it doesn't work.

r? saethlin as the instantiation guy

Procedurally, I think this should be fine to merge without any lang involvement, as this only does a very minor extension to an existing lint.

1 files changed, 4 insertions, 0 deletions

diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 06398dd4f72..bea86801ed7 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -383,6 +383,10 @@ passes_inline_ignored_constants =
     .warn = {-passes_previously_accepted}
     .note = {-passes_see_issue(issue: "65833")}
 
+passes_inline_ignored_for_exported =
+    `#[inline]` is ignored on externally exported functions
+    .help = externally exported functions are functions with `#[no_mangle]`, `#[export_name]`, or `#[linkage]`
+
 passes_inline_ignored_function_prototype =
     `#[inline]` is ignored on function prototypes