Auto merge of #87772 - npmccallum:naked_abi, r=Amanieu

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

2 files changed, 8 insertions, 14 deletions

diff --git a/src/test/ui/asm/naked-functions.rs b/src/test/ui/asm/naked-functions.rs
index 7075995c2cf..900f4443a1f 100644
--- a/src/test/ui/asm/naked-functions.rs
+++ b/src/test/ui/asm/naked-functions.rs
@@ -134,14 +134,12 @@ unsafe extern "C" fn invalid_options_continued() {
 #[naked]
 pub unsafe fn default_abi() {
     //~^ WARN Rust ABI is unsupported in naked functions
-    //~| WARN this was previously accepted
     asm!("", options(noreturn));
 }
 
 #[naked]
 pub unsafe extern "Rust" fn rust_abi() {
     //~^ WARN Rust ABI is unsupported in naked functions
-    //~| WARN this was previously accepted
     asm!("", options(noreturn));
 }
 
diff --git a/src/test/ui/asm/naked-functions.stderr b/src/test/ui/asm/naked-functions.stderr
index 2a186a69ff4..231a6239cbd 100644
--- a/src/test/ui/asm/naked-functions.stderr
+++ b/src/test/ui/asm/naked-functions.stderr
@@ -284,20 +284,16 @@ warning: Rust ABI is unsupported in naked functions
 LL | pub unsafe fn default_abi() {
    |               ^^^^^^^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
+   = note: `#[warn(undefined_naked_function_abi)]` on by default
 
 warning: Rust ABI is unsupported in naked functions
-  --> $DIR/naked-functions.rs:142:29
+  --> $DIR/naked-functions.rs:141:29
    |
 LL | pub unsafe extern "Rust" fn rust_abi() {
    |                             ^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:177:1
+  --> $DIR/naked-functions.rs:175:1
    |
 LL | #[inline]
    | ^^^^^^^^^
@@ -306,7 +302,7 @@ LL | #[inline]
    = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:185:1
+  --> $DIR/naked-functions.rs:183:1
    |
 LL | #[inline(always)]
    | ^^^^^^^^^^^^^^^^^
@@ -315,7 +311,7 @@ LL | #[inline(always)]
    = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:193:1
+  --> $DIR/naked-functions.rs:191:1
    |
 LL | #[inline(never)]
    | ^^^^^^^^^^^^^^^^
@@ -324,7 +320,7 @@ LL | #[inline(never)]
    = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:201:1
+  --> $DIR/naked-functions.rs:199:1
    |
 LL | #[inline]
    | ^^^^^^^^^
@@ -333,7 +329,7 @@ LL | #[inline]
    = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:204:1
+  --> $DIR/naked-functions.rs:202:1
    |
 LL | #[inline(always)]
    | ^^^^^^^^^^^^^^^^^
@@ -342,7 +338,7 @@ LL | #[inline(always)]
    = note: for more information, see issue #32408 <https://github.com/rust-lang/rust/issues/32408>
 
 warning: naked functions cannot be inlined
-  --> $DIR/naked-functions.rs:207:1
+  --> $DIR/naked-functions.rs:205:1
    |
 LL | #[inline(never)]
    | ^^^^^^^^^^^^^^^^