Move naked function ABI check to its own lint

This check was previously categorized under the lint named
`UNSUPPORTED_NAKED_FUNCTIONS`. That lint is future incompatible and will
be turned into an error in a future release. However, as defined in the
Constrained Naked Functions RFC, this check should only be a warning.
This is because it is possible for a naked function to be implemented in
such a way that it does not break even the undefined ABI. For example, a
`jmp` to a `const`.

Therefore, this patch defines a new lint named
`UNDEFINED_NAKED_FUNCTION_ABI` which contains just this single check.
Unlike `UNSUPPORTED_NAKED_FUNCTIONS`, `UNDEFINED_NAKED_FUNCTION_ABI`
will not be converted to an error in the future.

rust-lang/rfcs#2774
rust-lang/rfcs#2972

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_passes/src/naked_functions.rs b/compiler/rustc_passes/src/naked_functions.rs
index e05ec205b65..899503cc556 100644
--- a/compiler/rustc_passes/src/naked_functions.rs
+++ b/compiler/rustc_passes/src/naked_functions.rs
@@ -7,6 +7,7 @@ use rustc_hir::intravisit::{ErasedMap, FnKind, NestedVisitorMap, Visitor};
 use rustc_hir::{ExprKind, HirId, InlineAsmOperand, StmtKind};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
+use rustc_session::lint::builtin::UNDEFINED_NAKED_FUNCTION_ABI;
 use rustc_session::lint::builtin::UNSUPPORTED_NAKED_FUNCTIONS;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
@@ -87,7 +88,7 @@ fn check_inline(tcx: TyCtxt<'_>, hir_id: HirId, attrs: &[Attribute]) {
 /// Checks that function uses non-Rust ABI.
 fn check_abi(tcx: TyCtxt<'_>, hir_id: HirId, abi: Abi, fn_ident_span: Span) {
     if abi == Abi::Rust {
-        tcx.struct_span_lint_hir(UNSUPPORTED_NAKED_FUNCTIONS, hir_id, fn_ident_span, |lint| {
+        tcx.struct_span_lint_hir(UNDEFINED_NAKED_FUNCTION_ABI, hir_id, fn_ident_span, |lint| {
             lint.build("Rust ABI is unsupported in naked functions").emit();
         });
     }