Rollup merge of #105455 - lcnr:correct-reveal-in-validate, r=jackh726

use the correct `Reveal` during validation

supersedes #105454. Deals with #105009 (comment), not closing #105009 as the ICE may leak into beta

The issue was the following:
- we optimize the mir, using `Reveal::All`
- some optimization relies on the hidden type of an opaque type
- we then validate using `Reveal::UserFacing` again which is not able to observe the hidden type

r? `@jackh726`

Author: matthiaskrgr

compiler/rustc_const_eval/src/transform/validate.rs

@@ -2,6 +2,7 @@
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_index::bit_set::BitSet;
+use rustc_infer::traits::Reveal;
 use rustc_middle::mir::interpret::Scalar;
 use rustc_middle::mir::visit::NonUseContext::VarDebugInfo;
 use rustc_middle::mir::visit::{PlaceContext, Visitor};
@@ -44,8 +45,11 @@ impl<'tcx> MirPass<'tcx> for Validator {
             return;
         }
         let def_id = body.source.def_id();
-        let param_env = tcx.param_env(def_id);
         let mir_phase = self.mir_phase;
+        let param_env = match mir_phase.reveal() {
+            Reveal::UserFacing => tcx.param_env(def_id),
+            Reveal::All => tcx.param_env_reveal_all_normalized(def_id),
+        };
 
         let always_live_locals = always_storage_live_locals(body);
         let storage_liveness = MaybeStorageLive::new(always_live_locals)

compiler/rustc_middle/src/mir/syntax.rs

@@ -6,6 +6,7 @@
 use super::{BasicBlock, Constant, Field, Local, SwitchTargets, UserTypeProjection};
 
 use crate::mir::coverage::{CodeRegion, CoverageKind};
+use crate::traits::Reveal;
 use crate::ty::adjustment::PointerCast;
 use crate::ty::subst::SubstsRef;
 use crate::ty::{self, List, Ty};
@@ -100,6 +101,13 @@ impl MirPhase {
             MirPhase::Runtime(RuntimePhase::Optimized) => "runtime-optimized",
         }
     }
+
+    pub fn reveal(&self) -> Reveal {
+        match *self {
+            MirPhase::Built | MirPhase::Analysis(_) => Reveal::UserFacing,
+            MirPhase::Runtime(_) => Reveal::All,
+        }
+    }
 }
 
 /// See [`MirPhase::Analysis`].

src/test/ui/mir/issue-95978-validator-lifetime-comparison.rs renamed to src/test/ui/mir/validate/issue-95978-validator-lifetime-comparison.rs

@@ -0,0 +1,52 @@
+// Regression test for #105009. the issue here was that even after the `RevealAll` pass,
+// `validate` still used `Reveal::UserFacing`. This meant that it now ends up comparing
+// opaque types with their revealed version, resulting in an ICE.
+//
+// We're using these flags to run the `RevealAll` pass while making it less likely to
+// accidentally removing the assignment from `Foo<fn_ptr>` to `Foo<fn_def>`.
+
+// compile-flags: -Zinline_mir=yes -Zmir-opt-level=0 -Zvalidate-mir
+// run-pass
+
+use std::hint::black_box;
+
+trait Func {
+    type Ret: Id;
+}
+
+trait Id {
+    type Assoc;
+}
+impl Id for u32 {
+    type Assoc = u32;
+}
+impl Id for i32 {
+    type Assoc = i32;
+}
+
+impl<F: FnOnce() -> R, R: Id> Func for F {
+    type Ret = R;
+}
+
+fn bar() -> impl Copy + Id {
+    0u32
+}
+
+struct Foo<T: Func> {
+    _func: T,
+    value: Option<<<T as Func>::Ret as Id>::Assoc>,
+}
+
+fn main() {
+    let mut fn_def = black_box(Foo {
+        _func: bar,
+        value: None,
+    });
+    let fn_ptr = black_box(Foo {
+        _func: bar as fn() -> _,
+        value: None,
+    });
+
+    fn_def.value = fn_ptr.value;
+    black_box(fn_def);
+}