Revert "Unify tcx.constness and param env constness checks"

This reverts commit bef8681a18.
This reverts commit c646c4d403.

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -25,10 +25,12 @@ pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
 /// report whether said intrinsic has a `rustc_const_{un,}stable` attribute. Otherwise, return
 /// `Constness::NotConst`.
 fn constness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Constness {
-    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
-    match tcx.hir().get(hir_id) {
-        hir::Node::Ctor(_) => hir::Constness::Const,
+    let def_id = def_id.expect_local();
+    let node = tcx.hir().get_by_def_id(def_id);
 
+    match node {
+        hir::Node::Ctor(_) => hir::Constness::Const,
+        hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(impl_), .. }) => impl_.constness,
         hir::Node::ForeignItem(hir::ForeignItem { kind: hir::ForeignItemKind::Fn(..), .. }) => {
             // Intrinsics use `rustc_const_{un,}stable` attributes to indicate constness. All other
             // foreign items cannot be evaluated at compile-time.
@@ -39,62 +41,20 @@ fn constness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Constness {
             };
             if is_const { hir::Constness::Const } else { hir::Constness::NotConst }
         }
+        _ => {
+            if let Some(fn_kind) = node.fn_kind() {
+                if fn_kind.constness() == hir::Constness::Const {
+                    return hir::Constness::Const;
+                }
 
-        hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
-            if tcx.is_const_default_method(def_id) =>
-        {
-            hir::Constness::Const
-        }
-
-        hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(..), .. })
-        | hir::Node::Item(hir::Item { kind: hir::ItemKind::Static(..), .. })
-        | hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Const(..), .. })
-        | hir::Node::AnonConst(_)
-        | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
-        | hir::Node::ImplItem(hir::ImplItem {
-            kind:
-                hir::ImplItemKind::Fn(
-                    hir::FnSig {
-                        header: hir::FnHeader { constness: hir::Constness::Const, .. },
-                        ..
-                    },
-                    ..,
-                ),
-            ..
-        }) => hir::Constness::Const,
-
-        hir::Node::ImplItem(hir::ImplItem {
-            kind: hir::ImplItemKind::Type(..) | hir::ImplItemKind::Fn(..),
-            ..
-        }) => {
-            let parent_hir_id = tcx.hir().get_parent_node(hir_id);
-            match tcx.hir().get(parent_hir_id) {
-                hir::Node::Item(hir::Item {
-                    kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
-                    ..
-                }) => *constness,
-                _ => span_bug!(
-                    tcx.def_span(parent_hir_id.owner),
-                    "impl item's parent node is not an impl",
-                ),
+                // If the function itself is not annotated with `const`, it may still be a `const fn`
+                // if it resides in a const trait impl.
+                let is_const = is_parent_const_impl_raw(tcx, def_id);
+                if is_const { hir::Constness::Const } else { hir::Constness::NotConst }
+            } else {
+                hir::Constness::NotConst
             }
         }
-
-        hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
-            ..
-        })
-        | hir::Node::TraitItem(hir::TraitItem {
-            kind:
-                hir::TraitItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
-            ..
-        })
-        | hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
-            ..
-        }) => *constness,
-
-        _ => hir::Constness::NotConst,
     }
 }
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1059,43 +1059,6 @@ fn should_encode_const(def_kind: DefKind) -> bool {
     }
 }
 
-fn should_encode_constness(def_kind: DefKind) -> bool {
-    match def_kind {
-        DefKind::Struct
-        | DefKind::Union
-        | DefKind::Enum
-        | DefKind::Trait
-        | DefKind::AssocTy
-        | DefKind::Fn
-        | DefKind::Const
-        | DefKind::Static(..)
-        | DefKind::Ctor(..)
-        | DefKind::AssocFn
-        | DefKind::AssocConst
-        | DefKind::AnonConst
-        | DefKind::InlineConst
-        | DefKind::OpaqueTy
-        | DefKind::ImplTraitPlaceholder
-        | DefKind::Impl
-        | DefKind::Closure
-        | DefKind::Generator
-        | DefKind::TyAlias => true,
-        DefKind::Variant
-        | DefKind::TraitAlias
-        | DefKind::ForeignTy
-        | DefKind::Field
-        | DefKind::TyParam
-        | DefKind::Mod
-        | DefKind::ForeignMod
-        | DefKind::ConstParam
-        | DefKind::Macro(..)
-        | DefKind::Use
-        | DefKind::LifetimeParam
-        | DefKind::GlobalAsm
-        | DefKind::ExternCrate => false,
-    }
-}
-
 fn should_encode_trait_impl_trait_tys<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
     if tcx.def_kind(def_id) != DefKind::AssocFn {
         return false;
@@ -1202,9 +1165,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             {
                 record!(self.tables.trait_impl_trait_tys[def_id] <- table);
             }
-            if should_encode_constness(def_kind) {
-                self.tables.constness.set(def_id.index, tcx.constness(def_id));
-            }
         }
         let inherent_impls = tcx.crate_inherent_impls(());
         for (def_id, implementations) in inherent_impls.inherent_impls.iter() {
@@ -1232,6 +1192,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         };
 
         record!(self.tables.variant_data[def_id] <- data);
+        self.tables.constness.set(def_id.index, hir::Constness::Const);
         record_array!(self.tables.children[def_id] <- variant.fields.iter().map(|f| {
             assert!(f.did.is_local());
             f.did.index
@@ -1259,6 +1220,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         };
 
         record!(self.tables.variant_data[def_id] <- data);
+        self.tables.constness.set(def_id.index, hir::Constness::Const);
         if variant.ctor_kind == CtorKind::Fn {
             record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
         }
@@ -1322,6 +1284,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         record!(self.tables.repr_options[def_id] <- adt_def.repr());
         record!(self.tables.variant_data[def_id] <- data);
+        self.tables.constness.set(def_id.index, hir::Constness::Const);
         if variant.ctor_kind == CtorKind::Fn {
             record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
         }
@@ -1357,6 +1320,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     }
                 };
                 self.tables.asyncness.set(def_id.index, m_sig.header.asyncness);
+                self.tables.constness.set(def_id.index, hir::Constness::NotConst);
             }
             ty::AssocKind::Type => {
                 self.encode_explicit_item_bounds(def_id);
@@ -1381,6 +1345,13 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 let hir::ImplItemKind::Fn(ref sig, body) = ast_item.kind else { bug!() };
                 self.tables.asyncness.set(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
+                // Can be inside `impl const Trait`, so using sig.header.constness is not reliable
+                let constness = if self.tcx.is_const_fn_raw(def_id) {
+                    hir::Constness::Const
+                } else {
+                    hir::Constness::NotConst
+                };
+                self.tables.constness.set(def_id.index, constness);
             }
             ty::AssocKind::Const | ty::AssocKind::Type => {}
         }
@@ -1503,6 +1474,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             hir::ItemKind::Fn(ref sig, .., body) => {
                 self.tables.asyncness.set(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
+                self.tables.constness.set(def_id.index, sig.header.constness);
             }
             hir::ItemKind::Macro(ref macro_def, _) => {
                 if macro_def.macro_rules {
@@ -1523,6 +1495,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             hir::ItemKind::Struct(ref struct_def, _) => {
                 let adt_def = self.tcx.adt_def(def_id);
                 record!(self.tables.repr_options[def_id] <- adt_def.repr());
+                self.tables.constness.set(def_id.index, hir::Constness::Const);
 
                 // Encode def_ids for each field and method
                 // for methods, write all the stuff get_trait_method
@@ -1551,8 +1524,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     is_non_exhaustive: variant.is_field_list_non_exhaustive(),
                 });
             }
-            hir::ItemKind::Impl(hir::Impl { defaultness, .. }) => {
+            hir::ItemKind::Impl(hir::Impl { defaultness, constness, .. }) => {
                 self.tables.impl_defaultness.set(def_id.index, *defaultness);
+                self.tables.constness.set(def_id.index, *constness);
 
                 let trait_ref = self.tcx.impl_trait_ref(def_id);
                 if let Some(trait_ref) = trait_ref {

compiler/rustc_ty_utils/src/ty.rs

@@ -137,10 +137,77 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     let local_did = def_id.as_local();
     let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
 
+    let constness = match hir_id {
+        Some(hir_id) => match tcx.hir().get(hir_id) {
+            hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
+                if tcx.is_const_default_method(def_id) =>
+            {
+                hir::Constness::Const
+            }
+
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(..), .. })
+            | hir::Node::Item(hir::Item { kind: hir::ItemKind::Static(..), .. })
+            | hir::Node::TraitItem(hir::TraitItem {
+                kind: hir::TraitItemKind::Const(..), ..
+            })
+            | hir::Node::AnonConst(_)
+            | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
+            | hir::Node::ImplItem(hir::ImplItem {
+                kind:
+                    hir::ImplItemKind::Fn(
+                        hir::FnSig {
+                            header: hir::FnHeader { constness: hir::Constness::Const, .. },
+                            ..
+                        },
+                        ..,
+                    ),
+                ..
+            }) => hir::Constness::Const,
+
+            hir::Node::ImplItem(hir::ImplItem {
+                kind: hir::ImplItemKind::Type(..) | hir::ImplItemKind::Fn(..),
+                ..
+            }) => {
+                let parent_hir_id = tcx.hir().get_parent_node(hir_id);
+                match tcx.hir().get(parent_hir_id) {
+                    hir::Node::Item(hir::Item {
+                        kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
+                        ..
+                    }) => *constness,
+                    _ => span_bug!(
+                        tcx.def_span(parent_hir_id.owner),
+                        "impl item's parent node is not an impl",
+                    ),
+                }
+            }
+
+            hir::Node::Item(hir::Item {
+                kind:
+                    hir::ItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
+                ..
+            })
+            | hir::Node::TraitItem(hir::TraitItem {
+                kind:
+                    hir::TraitItemKind::Fn(
+                        hir::FnSig { header: hir::FnHeader { constness, .. }, .. },
+                        ..,
+                    ),
+                ..
+            })
+            | hir::Node::Item(hir::Item {
+                kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
+                ..
+            }) => *constness,
+
+            _ => hir::Constness::NotConst,
+        },
+        None => hir::Constness::NotConst,
+    };
+
     let unnormalized_env = ty::ParamEnv::new(
         tcx.intern_predicates(&predicates),
         traits::Reveal::UserFacing,
-        tcx.constness(def_id),
+        constness,
     );
 
     let body_id =