Rollup merge of #128580 - compiler-errors:cfi-param-env, r=lcnr

Use `ParamEnv::reveal_all` in CFI

I left a huge comment for why this ICEs in the test I committed.

`typeid_for_instance` should only be called on monomorphic instances during codegen, and we should just be using `ParamEnv::reveal_all()` rather than the param-env of the instance itself. I added an assertion to ensure that we only do this for fully substituted instances (this may break with polymorphization, but I kinda don't care lol).

Fixes #114160
cc `@rcvalle`

compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/mod.rs

@@ -6,7 +6,7 @@
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_middle::bug;
-use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_target::abi::call::{Conv, FnAbi, PassMode};
 use tracing::instrument;
 
@@ -112,11 +112,12 @@ pub fn typeid_for_instance<'tcx>(
     instance: Instance<'tcx>,
     options: TypeIdOptions,
 ) -> String {
+    assert!(!instance.has_non_region_param(), "{instance:#?} must be fully monomorphic");
     let transform_ty_options = TransformTyOptions::from_bits(options.bits())
         .unwrap_or_else(|| bug!("typeid_for_instance: invalid option(s) `{:?}`", options.bits()));
     let instance = transform_instance(tcx, instance, transform_ty_options);
     let fn_abi = tcx
-        .fn_abi_of_instance(tcx.param_env(instance.def_id()).and((instance, ty::List::empty())))
+        .fn_abi_of_instance(ty::ParamEnv::reveal_all().and((instance, ty::List::empty())))
         .unwrap_or_else(|error| {
             bug!("typeid_for_instance: couldn't get fn_abi of instance {instance:?}: {error:?}")
         });

tests/ui/sanitizer/cfi-can-reveal-opaques.rs

@@ -0,0 +1,44 @@
+//@ needs-sanitizer-cfi
+//@ compile-flags: -Ccodegen-units=1 -Clto -Ctarget-feature=-crt-static -Zsanitizer=cfi
+//@ no-prefer-dynamic
+//@ only-x86_64-unknown-linux-gnu
+//@ build-pass
+
+// See comment below for why this test exists.
+
+trait Tr<U> {
+    type Projection;
+}
+
+impl<F, U> Tr<U> for F
+where
+    F: Fn() -> U
+{
+    type Projection = U;
+}
+
+fn test<B: Tr<U>, U>(b: B) -> B::Projection
+{
+    todo!()
+}
+
+fn main() {
+    fn rpit_fn() -> impl Sized {}
+
+    // When CFI runs, it tries to compute the signature of the call. This
+    // ends up giving us a signature of:
+    //     `fn test::<rpit_fn, ()>() -> <rpit_fn as Tr<()>>::Projection`,
+    // where `rpit_fn` is the ZST FnDef for the function. However, we were
+    // previously using a Reveal::UserFacing param-env. This means that the
+    // `<rpit_fn as Tr<()>>::Projection` return type is impossible to normalize,
+    // since it would require proving `rpit_fn: Fn() -> ()`, but we cannot
+    // prove that the `impl Sized` opaque is `()` with a user-facing param-env.
+    // This leads to a normalization error, and then an ICE.
+    //
+    // Side-note:
+    // So why is the second generic of `test` "`()`", and not the
+    // `impl Sized` since we inferred it from the return type of `rpit_fn`
+    // during typeck? Well, that's because we're using the generics from the
+    // terminator of the MIR, which has had the RevealAll pass performed on it.
+    let _ = test(rpit_fn);
+}