use TypingEnv when no infcx is available

the behavior of the type system not only depends on the current
assumptions, but also the currentnphase of the compiler. This is
mostly necessary as we need to decide whether and how to reveal
opaque types. We track this via the `TypingMode`.

compiler/rustc_mir_transform/src/large_enums.rs

@@ -3,7 +3,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::mir::*;
 use rustc_middle::ty::util::IntTypeExt;
-use rustc_middle::ty::{self, AdtDef, ParamEnv, Ty, TyCtxt};
+use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
 use rustc_session::Session;
 
 /// A pass that seeks to optimize unnecessary moves of large enum types, if there is a large
@@ -39,8 +39,7 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
         // platform, but it will still be valid.
 
         let mut alloc_cache = FxHashMap::default();
-        let body_did = body.source.def_id();
-        let param_env = tcx.param_env_reveal_all_normalized(body_did);
+        let typing_env = body.typing_env(tcx);
 
         let blocks = body.basic_blocks.as_mut();
         let local_decls = &mut body.local_decls;
@@ -58,7 +57,7 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
                 let ty = lhs.ty(local_decls, tcx).ty;
 
                 let (adt_def, num_variants, alloc_id) =
-                    self.candidate(tcx, param_env, ty, &mut alloc_cache)?;
+                    self.candidate(tcx, typing_env, ty, &mut alloc_cache)?;
 
                 let source_info = st.source_info;
                 let span = source_info.span;
@@ -207,7 +206,7 @@ impl EnumSizeOpt {
     fn candidate<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,
-        param_env: ParamEnv<'tcx>,
+        typing_env: ty::TypingEnv<'tcx>,
         ty: Ty<'tcx>,
         alloc_cache: &mut FxHashMap<Ty<'tcx>, AllocId>,
     ) -> Option<(AdtDef<'tcx>, usize, AllocId)> {
@@ -215,7 +214,7 @@ impl EnumSizeOpt {
             ty::Adt(adt_def, _args) if adt_def.is_enum() => adt_def,
             _ => return None,
         };
-        let layout = tcx.layout_of(param_env.and(ty)).ok()?;
+        let layout = tcx.layout_of(typing_env.as_query_input(ty)).ok()?;
         let variants = match &layout.variants {
             Variants::Single { .. } => return None,
             Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => return None,