Make DropShim's param_env optional to fix InstanceKind::DropShim

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -111,7 +111,11 @@ pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
     fn patch(&mut self) -> &mut MirPatch<'tcx>;
     fn body(&self) -> &'a Body<'tcx>;
     fn tcx(&self) -> TyCtxt<'tcx>;
-    fn param_env(&self) -> ty::ParamEnv<'tcx>;
+
+    // A param-env that can be used to compute drop queries (such as `Ty::needs_drop`).
+    // If this is `None`, then the elaborator must handle the type as if it were unknown,
+    // i.e. emitting full drops.
+    fn param_env(&self) -> Option<ty::ParamEnv<'tcx>>;
 
     // Drop logic
 
@@ -276,9 +280,11 @@ where
                 let subpath = self.elaborator.field_subpath(variant_path, field);
                 let tcx = self.tcx();
 
-                assert_eq!(self.elaborator.param_env().reveal(), Reveal::All);
-                let field_ty =
-                    tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, args));
+                let mut field_ty = f.ty(tcx, args);
+                if let Some(param_env) = self.elaborator.param_env() {
+                    assert_eq!(param_env.reveal(), Reveal::All);
+                    field_ty = tcx.normalize_erasing_regions(param_env, field_ty);
+                }
 
                 (tcx.mk_place_field(base_place, field, field_ty), subpath)
             })
@@ -374,9 +380,9 @@ where
         debug!("drop_ladder({:?}, {:?})", self, fields);
 
         let mut fields = fields;
-        fields.retain(|&(place, _)| {
-            self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
-        });
+        if let Some(param_env) = self.elaborator.param_env() {
+            fields.retain(|&(place, _)| self.place_ty(place).needs_drop(self.tcx(), param_env));
+        }
 
         debug!("drop_ladder - fields needing drop: {:?}", fields);
 
@@ -548,10 +554,13 @@ where
                 have_otherwise = true;
 
                 let param_env = self.elaborator.param_env();
-                let have_field_with_drop_glue = variant
-                    .fields
-                    .iter()
-                    .any(|field| field.ty(tcx, args).needs_drop(tcx, param_env));
+
+                let have_field_with_drop_glue = param_env.is_none_or(|param_env| {
+                    variant
+                        .fields
+                        .iter()
+                        .any(|field| field.ty(tcx, args).needs_drop(tcx, param_env))
+                });
                 if have_field_with_drop_glue {
                     have_otherwise_with_drop_glue = true;
                 }
@@ -869,7 +878,10 @@ where
             ty::Adt(def, args) => self.open_drop_for_adt(*def, args),
             ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
             ty::Array(ety, size) => {
-                let size = size.try_eval_target_usize(self.tcx(), self.elaborator.param_env());
+                let size = self
+                    .elaborator
+                    .param_env()
+                    .and_then(|param_env| size.try_eval_target_usize(self.tcx(), param_env));
                 self.open_drop_for_array(*ety, size)
             }
             ty::Slice(ety) => self.drop_loop_pair(*ety),

compiler/rustc_mir_dataflow/src/lib.rs

@@ -2,6 +2,7 @@
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(exact_size_is_empty)]
+#![feature(is_none_or)]
 #![feature(let_chains)]
 #![feature(try_blocks)]
 // tidy-alphabetical-end

compiler/rustc_mir_transform/src/coroutine.rs

@@ -1174,7 +1174,8 @@ fn elaborate_coroutine_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let def_id = body.source.def_id();
     let param_env = tcx.param_env(def_id);
 
-    let mut elaborator = DropShimElaborator { body, patch: MirPatch::new(body), tcx, param_env };
+    let mut elaborator =
+        DropShimElaborator { body, patch: MirPatch::new(body), tcx, param_env: Some(param_env) };
 
     for (block, block_data) in body.basic_blocks.iter_enumerated() {
         let (target, unwind, source_info) = match block_data.terminator() {

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -161,8 +161,8 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, '_, 'tcx> {
         self.ctxt.tcx
     }
 
-    fn param_env(&self) -> ty::ParamEnv<'tcx> {
-        self.ctxt.param_env()
+    fn param_env(&self) -> Option<ty::ParamEnv<'tcx>> {
+        Some(self.ctxt.param_env())
     }
 
     #[instrument(level = "debug", skip(self), ret)]

compiler/rustc_mir_transform/src/inline.rs

@@ -12,9 +12,7 @@ use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{
-    self, Instance, InstanceKind, ParamEnv, Ty, TyCtxt, TypeFlags, TypeVisitableExt,
-};
+use rustc_middle::ty::{self, Instance, InstanceKind, ParamEnv, Ty, TyCtxt};
 use rustc_session::config::{DebugInfo, OptLevel};
 use rustc_span::source_map::Spanned;
 use rustc_span::sym;
@@ -207,7 +205,7 @@ impl<'tcx> Inliner<'tcx> {
             }
         }
 
-        let callee_body = try_instance_mir(self.tcx, callsite.callee.def)?;
+        let callee_body = self.tcx.instance_mir(callsite.callee.def);
         self.check_mir_body(callsite, callee_body, callee_attrs, cross_crate_inlinable)?;
 
         if !self.tcx.consider_optimizing(|| {
@@ -323,15 +321,6 @@ impl<'tcx> Inliner<'tcx> {
                 return Err("instance without MIR (intrinsic / virtual)");
             }
 
-            // FIXME(#127030): `ConstParamHasTy` has bad interactions with
-            // the drop shim builder, which does not evaluate predicates in
-            // the correct param-env for types being dropped. Stall resolving
-            // the MIR for this instance until all of its const params are
-            // substituted.
-            InstanceKind::DropGlue(_, Some(ty)) if ty.has_type_flags(TypeFlags::HAS_CT_PARAM) => {
-                return Err("still needs substitution");
-            }
-
             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
             // do not need to catch this here, we can wait until the inliner decides to continue
@@ -1100,26 +1089,6 @@ impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
     }
 }
 
-#[instrument(skip(tcx), level = "debug")]
-fn try_instance_mir<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    instance: InstanceKind<'tcx>,
-) -> Result<&'tcx Body<'tcx>, &'static str> {
-    if let ty::InstanceKind::DropGlue(_, Some(ty))
-    | ty::InstanceKind::AsyncDropGlueCtorShim(_, Some(ty)) = instance
-        && let ty::Adt(def, args) = ty.kind()
-    {
-        let fields = def.all_fields();
-        for field in fields {
-            let field_ty = field.ty(tcx, args);
-            if field_ty.has_param() && field_ty.has_aliases() {
-                return Err("cannot build drop shim for polymorphic type");
-            }
-        }
-    }
-    Ok(tcx.instance_mir(instance))
-}
-
 fn body_is_forwarder(body: &Body<'_>) -> bool {
     let TerminatorKind::Call { target, .. } = body.basic_blocks[START_BLOCK].terminator().kind
     else {

compiler/rustc_mir_transform/src/shim.rs

@@ -9,7 +9,7 @@ use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{
-    self, CoroutineArgs, CoroutineArgsExt, EarlyBinder, GenericArgs, Ty, TyCtxt,
+    self, CoroutineArgs, CoroutineArgsExt, EarlyBinder, GenericArgs, Ty, TyCtxt, TypeVisitableExt,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::elaborate_drops::{self, DropElaborator, DropFlagMode, DropStyle};
@@ -276,7 +276,8 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)
 
     if ty.is_some() {
         let patch = {
-            let param_env = tcx.param_env_reveal_all_normalized(def_id);
+            let param_env =
+                if ty.has_non_region_param() { None } else { Some(ty::ParamEnv::reveal_all()) };
             let mut elaborator =
                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
             let dropee = tcx.mk_place_deref(dropee_ptr);
@@ -336,7 +337,7 @@ pub struct DropShimElaborator<'a, 'tcx> {
     pub body: &'a Body<'tcx>,
     pub patch: MirPatch<'tcx>,
     pub tcx: TyCtxt<'tcx>,
-    pub param_env: ty::ParamEnv<'tcx>,
+    pub param_env: Option<ty::ParamEnv<'tcx>>,
 }
 
 impl fmt::Debug for DropShimElaborator<'_, '_> {
@@ -357,7 +358,7 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
-    fn param_env(&self) -> ty::ParamEnv<'tcx> {
+    fn param_env(&self) -> Option<ty::ParamEnv<'tcx>> {
         self.param_env
     }