Auto merge of #148602 - BoxyUwU:coercion_cleanup_uncontroversial, r=lcnr

misc coercion cleanups and handle safety correctly

r? lcnr

### "remove normalize call"

Fixes #132765

If the normalization fails we would sometimes get a `TypeError` containing inference variables created inside of the probe used by coercion. These would then get leaked out causing ICEs in diagnostics logic

### "leak check and lub for closure<->closure coerce-lubs of same defids"

Fixes rust-lang/trait-system-refactor-initiative#233
```rust
fn peculiar() -> impl Fn(u8) -> u8 {
    return |x| x + 1
}
```
the `|x| x + 1` expr has a type of `Closure(?31t)` which we wind up inferring the RPIT to. The `CoerceMany` `ret_coercion` for the whole `peculiar` typeck has an expected type of `RPIT` (unnormalized). When we type check the `return |x| x + 1` expr we go from the never type to `Closure(?31t)` which then participates in the `ret_coercion` giving us a `coerce-lub(RPIT, Closure(?31t))`.

Normalizing `RPIT` gives us some `Closure(?50t)` where `?31t` and `?50t` have been unified with `?31t` as the root var. `resolve_vars_if_possible` doesn't resolve infer vars to their roots so these wind up with different structural identities so the fast path doesn't apply and we fall back to coercing to a `fn` ptr. cc #147193 which also fixes this

New solver probably just gets more inference variables here because canonicalization + generally different approach to normalization of opaques. Idk :3

### FCP worthy stuffy

there are some other FCP worthy things but they're in my FCP comment which also contains some analysis of the breaking nature of the previously listed changes in this PR: #148602 (comment)

Author: bors

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1061,7 +1061,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
 
             Rvalue::Cast(cast_kind, op, ty) => {
                 match *cast_kind {
-                    CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, coercion_source) => {
+                    CastKind::PointerCoercion(
+                        PointerCoercion::ReifyFnPointer(target_safety),
+                        coercion_source,
+                    ) => {
                         let is_implicit_coercion = coercion_source == CoercionSource::Implicit;
                         let src_ty = op.ty(self.body, tcx);
                         let mut src_sig = src_ty.fn_sig(tcx);
@@ -1078,6 +1081,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                             src_sig = safe_sig;
                         }
 
+                        if src_sig.safety().is_safe() && target_safety.is_unsafe() {
+                            src_sig = tcx.safe_to_unsafe_sig(src_sig);
+                        }
+
                         // HACK: This shouldn't be necessary... We can remove this when we actually
                         // get binders with where clauses, then elaborate implied bounds into that
                         // binder, and implement a higher-ranked subtyping algorithm that actually

compiler/rustc_codegen_cranelift/src/base.rs

@@ -689,7 +689,7 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                     lval.write_cvalue(fx, res);
                 }
                 Rvalue::Cast(
-                    CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _),
+                    CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer(_), _),
                     ref operand,
                     to_ty,
                 ) => {

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -405,7 +405,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         let lladdr = bx.ptrtoint(llptr, llcast_ty);
                         OperandValue::Immediate(lladdr)
                     }
-                    mir::CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
+                    mir::CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer(_), _) => {
                         match *operand.layout.ty.kind() {
                             ty::FnDef(def_id, args) => {
                                 let instance = ty::Instance::resolve_for_fn_ptr(

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -627,7 +627,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     | PointerCoercion::ArrayToPointer
                     | PointerCoercion::UnsafeFnPointer
                     | PointerCoercion::ClosureFnPointer(_)
-                    | PointerCoercion::ReifyFnPointer,
+                    | PointerCoercion::ReifyFnPointer(_),
                     _,
                 ),
                 _,

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -74,7 +74,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 bug!("{cast_kind:?} casts are for borrowck only, not runtime MIR");
             }
 
-            CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
+            CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer(_), _) => {
                 // All reifications must be monomorphic, bail out otherwise.
                 ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;