add is_host_effect to GenericParamDefKind::Const and address review

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -523,7 +523,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             Ty::new_misc_error(tcx).into()
                         }
                     }
-                    GenericParamDefKind::Const { has_default } => {
+                    GenericParamDefKind::Const { has_default, .. } => {
                         let ty = tcx
                             .at(self.span)
                             .type_of(param.def_id)

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1255,7 +1255,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
 
     let is_our_default = |def: &ty::GenericParamDef| match def.kind {
         GenericParamDefKind::Type { has_default, .. }
-        | GenericParamDefKind::Const { has_default } => {
+        | GenericParamDefKind::Const { has_default, .. } => {
             has_default && def.index >= generics.parent_count as u32
         }
         GenericParamDefKind::Lifetime => unreachable!(),

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -328,7 +328,10 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 name: param.name.ident().name,
                 def_id: param.def_id.to_def_id(),
                 pure_wrt_drop: param.pure_wrt_drop,
-                kind: ty::GenericParamDefKind::Const { has_default: default.is_some() },
+                kind: ty::GenericParamDefKind::Const {
+                    has_default: default.is_some(),
+                    is_host_effect: is_host_param,
+                },
             })
         }
     }));

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1295,10 +1295,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ty_infer(Some(param), inf.span).into()
                     }
-                    (&GenericParamDefKind::Const { has_default }, GenericArg::Infer(inf)) => {
+                    (
+                        &GenericParamDefKind::Const { has_default, is_host_effect },
+                        GenericArg::Infer(inf),
+                    ) => {
                         let tcx = self.fcx.tcx();
 
-                        if has_default && tcx.has_attr(param.def_id, sym::rustc_host) {
+                        if has_default && is_host_effect {
                             self.fcx.var_for_effect(param)
                         } else {
                             self.fcx
@@ -1341,7 +1344,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             self.fcx.var_for_def(self.span, param)
                         }
                     }
-                    GenericParamDefKind::Const { has_default } => {
+                    GenericParamDefKind::Const { has_default, is_host_effect } => {
                         if has_default {
                             // N.B. this is a bit of a hack. `infer_args` is passed depending on
                             // whether the user has provided generic args. E.g. for `Vec::new`
@@ -1352,7 +1355,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             // it before falling back to default, such that a `const fn` such as
                             // `needs_drop::<()>` can still be called in const contexts. (if we defaulted
                             // instead of inferred, typeck would error)
-                            if tcx.has_attr(param.def_id, sym::rustc_host) {
+                            if is_host_effect {
                                 return self.fcx.var_for_effect(param);
                             } else if !infer_args {
                                 return tcx

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -20,7 +20,7 @@ use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKin
 use rustc_middle::ty::{self, Const, Ty, TyCtxt, TypeVisitableExt};
 use rustc_session::Session;
 use rustc_span::symbol::Ident;
-use rustc_span::{self, sym, Span, DUMMY_SP};
+use rustc_span::{self, Span, DUMMY_SP};
 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode, ObligationCtxt};
 
 use std::cell::{Cell, RefCell};
@@ -268,9 +268,12 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
     ) -> Const<'tcx> {
         // FIXME ideally this shouldn't use unwrap
         match param {
-            Some(param) if self.tcx.has_attr(param.def_id, sym::rustc_host) => {
+            Some(
-                self.var_for_effect(param).as_const().unwrap()
+                param @ ty::GenericParamDef {
-            }
+                    kind: ty::GenericParamDefKind::Const { is_host_effect: true, .. },
+                    ..
+                },
+            ) => self.var_for_effect(param).as_const().unwrap(),
             Some(param) => self.var_for_def(span, param).as_const().unwrap(),
             None => self.next_const_var(
                 ty,

compiler/rustc_infer/src/infer/combine.rs

@@ -546,9 +546,9 @@ fn float_unification_error<'tcx>(
 }
 
 fn effect_unification_error<'tcx>(
-    tcx: TyCtxt<'tcx>,
+    _tcx: TyCtxt<'tcx>,
-    a_is_expected: bool,
+    _a_is_expected: bool,
-    (a, b): (EffectVarValue<'tcx>, EffectVarValue<'tcx>),
+    (_a, _b): (EffectVarValue<'tcx>, EffectVarValue<'tcx>),
 ) -> TypeError<'tcx> {
-    TypeError::ConstMismatch(ExpectedFound::new(a_is_expected, a.as_const(tcx), b.as_const(tcx)))
+    bug!("unexpected effect unification error")
 }

compiler/rustc_infer/src/infer/mod.rs

@@ -36,7 +36,7 @@ use rustc_middle::ty::{self, GenericParamDefKind, InferConst, InferTy, Ty, TyCtx
 use rustc_middle::ty::{ConstVid, EffectVid, FloatVid, IntVid, TyVid};
 use rustc_middle::ty::{GenericArg, GenericArgKind, GenericArgs, GenericArgsRef};
 use rustc_span::symbol::Symbol;
-use rustc_span::{sym, Span};
+use rustc_span::Span;
 
 use std::cell::{Cell, RefCell};
 use std::fmt;
@@ -1181,9 +1181,8 @@ impl<'tcx> InferCtxt<'tcx> {
 
                 Ty::new_var(self.tcx, ty_var_id).into()
             }
-            GenericParamDefKind::Const { .. } => {
+            GenericParamDefKind::Const { is_host_effect, .. } => {
-                // todo what about using effect var here
+                if is_host_effect {
-                if self.tcx.has_attr(param.def_id, sym::rustc_host) {
                     return self.var_for_effect(param);
                 }
                 let origin = ConstVariableOrigin {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -873,14 +873,14 @@ fn should_encode_attrs(def_kind: DefKind) -> bool {
         | DefKind::AssocConst
         | DefKind::Macro(_)
         | DefKind::Field
-        | DefKind::Impl { .. }
+        | DefKind::Impl { .. } => true,
-        | DefKind::ConstParam => true,
         // Tools may want to be able to detect their tool lints on
         // closures from upstream crates, too. This is used by
         // https://github.com/model-checking/kani and is not a performance
         // or maintenance issue for us.
         DefKind::Closure => true,
         DefKind::TyParam
+        | DefKind::ConstParam
         | DefKind::Ctor(..)
         | DefKind::ExternCrate
         | DefKind::Use

compiler/rustc_middle/src/infer/canonical.rs

@@ -448,7 +448,6 @@ impl<'tcx> CanonicalVarValues<'tcx> {
                             };
                             ty::Region::new_late_bound(tcx, ty::INNERMOST, br).into()
                         }
-                        // todo eh?
                         CanonicalVarKind::Effect => ty::Const::new_bound(
                             tcx,
                             ty::INNERMOST,

compiler/rustc_middle/src/ty/generics.rs

@@ -12,7 +12,7 @@ use super::{Clause, EarlyBoundRegion, InstantiatedPredicates, ParamConst, ParamT
 pub enum GenericParamDefKind {
     Lifetime,
     Type { has_default: bool, synthetic: bool },
-    Const { has_default: bool },
+    Const { has_default: bool, is_host_effect: bool },
 }
 
 impl GenericParamDefKind {
@@ -87,7 +87,7 @@ impl GenericParamDef {
             GenericParamDefKind::Type { has_default, .. } if has_default => {
                 Some(tcx.type_of(self.def_id).map_bound(|t| t.into()))
             }
-            GenericParamDefKind::Const { has_default } if has_default => {
+            GenericParamDefKind::Const { has_default, .. } if has_default => {
                 Some(tcx.const_param_default(self.def_id).map_bound(|c| c.into()))
             }
             _ => None,
@@ -187,7 +187,7 @@ impl<'tcx> Generics {
                 GenericParamDefKind::Type { has_default, .. } => {
                     own_defaults.types += has_default as usize;
                 }
-                GenericParamDefKind::Const { has_default } => {
+                GenericParamDefKind::Const { has_default, .. } => {
                     own_defaults.consts += has_default as usize;
                 }
             }

compiler/rustc_privacy/src/lib.rs

@@ -836,7 +836,7 @@ impl ReachEverythingInTheInterfaceVisitor<'_, '_> {
                         self.visit(self.ev.tcx.type_of(param.def_id).instantiate_identity());
                     }
                 }
-                GenericParamDefKind::Const { has_default } => {
+                GenericParamDefKind::Const { has_default, .. } => {
                     self.visit(self.ev.tcx.type_of(param.def_id).instantiate_identity());
                     if has_default {
                         self.visit(

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -1242,7 +1242,7 @@ impl<'tcx> Stable<'tcx> for rustc_middle::ty::GenericParamDefKind {
             ty::GenericParamDefKind::Type { has_default, synthetic } => {
                 GenericParamDefKind::Type { has_default: *has_default, synthetic: *synthetic }
             }
-            ty::GenericParamDefKind::Const { has_default } => {
+            ty::GenericParamDefKind::Const { has_default, is_host_effect: _ } => {
                 GenericParamDefKind::Const { has_default: *has_default }
             }
         }

src/librustdoc/clean/mod.rs

@@ -541,7 +541,7 @@ fn clean_generic_param_def<'tcx>(
                 },
             )
         }
-        ty::GenericParamDefKind::Const { has_default } => (
+        ty::GenericParamDefKind::Const { has_default, .. } => (
             def.name,
             GenericParamDefKind::Const {
                 ty: Box::new(clean_middle_ty(