we can now enable the 'const stable fn must be stable' check

Author: RalfJung

compiler/rustc_error_codes/src/error_codes/E0539.md

@@ -45,6 +45,7 @@ const fn unstable_fn() {}
 #[stable(feature = "stable_struct", since = "1.39.0")] // ok!
 struct Stable;
 
+#[stable(feature = "stable_fn", since = "1.39.0")]
 #[rustc_const_stable(feature = "stable_fn", since = "1.39.0")] // ok!
 const fn stable_fn() {}
 ```

compiler/rustc_error_codes/src/error_codes/E0542.md

@@ -30,6 +30,7 @@ To fix this issue, you need to provide the `since` field. Example:
 #[stable(feature = "_stable_fn", since = "1.0.0")] // ok!
 fn _stable_fn() {}
 
+#[stable(feature = "_stable_const_fn", since = "1.0.0")]
 #[rustc_const_stable(feature = "_stable_const_fn", since = "1.0.0")] // ok!
 const fn _stable_const_fn() {}
 

compiler/rustc_passes/src/stability.rs

@@ -189,9 +189,6 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             && let Some(fn_sig) = fn_sig
             && const_stab.is_const_stable()
             && !stab.is_some_and(|(s, _)| s.is_stable())
-            // FIXME: we skip this check targets until
-            // <https://github.com/rust-lang/stdarch/pull/1654> propagates.
-            && false
         {
             self.tcx
                 .dcx()

tests/ui/consts/rustc-const-stability-require-const.rs

@@ -47,16 +47,15 @@ pub const fn foobar() {}
 pub const fn barfoo() {}
 
 // `rustc_const_stable` also requires the function to be stable.
-// FIXME: these are disabled until <https://github.com/rust-lang/stdarch/pull/1654> propagates.
 
 #[rustc_const_stable(feature = "barfoo_const", since = "1.0.0")]
 const fn barfoo_unmarked() {}
-// FIXME disabled ERROR can only be applied to functions that are declared `#[stable]`
+//~^ ERROR can only be applied to functions that are declared `#[stable]`
 
 #[unstable(feature = "unstable", issue = "none")]
 #[rustc_const_stable(feature = "barfoo_const", since = "1.0.0")]
 pub const fn barfoo_unstable() {}
-// FIXME disabled ERROR can only be applied to functions that are declared `#[stable]`
+//~^ ERROR can only be applied to functions that are declared `#[stable]`
 
 // `#[rustc_const_stable_indirect]` also requires a const fn
 #[rustc_const_stable_indirect]

tests/ui/consts/rustc-const-stability-require-const.stderr

@@ -70,17 +70,33 @@ help: make the function or method const
 LL | pub extern "C" fn foo_c() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
+error: attribute `#[rustc_const_stable]` can only be applied to functions that are declared `#[stable]`
+  --> $DIR/rustc-const-stability-require-const.rs:52:1
+   |
+LL | #[rustc_const_stable(feature = "barfoo_const", since = "1.0.0")]
+   | ---------------------------------------------------------------- attribute specified here
+LL | const fn barfoo_unmarked() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: attribute `#[rustc_const_stable]` can only be applied to functions that are declared `#[stable]`
+  --> $DIR/rustc-const-stability-require-const.rs:57:1
+   |
+LL | #[rustc_const_stable(feature = "barfoo_const", since = "1.0.0")]
+   | ---------------------------------------------------------------- attribute specified here
+LL | pub const fn barfoo_unstable() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: attributes `#[rustc_const_unstable]`, `#[rustc_const_stable]` and `#[rustc_const_stable_indirect]` require the function or method to be `const`
-  --> $DIR/rustc-const-stability-require-const.rs:64:1
+  --> $DIR/rustc-const-stability-require-const.rs:63:1
    |
 LL | pub fn not_a_const_fn() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: make the function or method const
-  --> $DIR/rustc-const-stability-require-const.rs:64:1
+  --> $DIR/rustc-const-stability-require-const.rs:63:1
    |
 LL | pub fn not_a_const_fn() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: aborting due to 9 previous errors