hir: Create hir::ConstArgKind enum

This will allow lowering const params to a dedicated enum variant, rather
than to an `AnonConst` that is later examined during `ty` lowering.

compiler/rustc_ast_lowering/src/lib.rs

@@ -49,9 +49,9 @@ use rustc_data_structures::sorted_map::SortedMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{DiagArgFromDisplay, DiagCtxt, StashKey};
-use rustc_hir as hir;
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{LocalDefId, LocalDefIdMap, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::{self as hir, ConstArgKind};
 use rustc_hir::{
     ConstArg, GenericArg, HirId, ItemLocalMap, MissingLifetimeKind, ParamName, TraitCandidate,
 };
@@ -1185,7 +1185,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                     })
                                 });
                                 return GenericArg::Const(ConstArg {
-                                    value: ct,
+                                    kind: ConstArgKind::Anon(ct),
                                     is_desugared_from_effects: false,
                                 });
                             }
@@ -1196,7 +1196,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 GenericArg::Type(self.lower_ty(ty, itctx))
             }
             ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
-                value: self.lower_anon_const(ct),
+                kind: ConstArgKind::Anon(self.lower_anon_const(ct)),
                 is_desugared_from_effects: false,
             }),
         }
@@ -2654,7 +2654,12 @@ impl<'hir> GenericArgsCtor<'hir> {
 
         lcx.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
         self.args.push(hir::GenericArg::Const(hir::ConstArg {
-            value: lcx.arena.alloc(hir::AnonConst { def_id, hir_id, body, span }),
+            kind: hir::ConstArgKind::Anon(lcx.arena.alloc(hir::AnonConst {
+                def_id,
+                hir_id,
+                body,
+                span,
+            })),
             is_desugared_from_effects: true,
         }))
     }

compiler/rustc_hir/src/hir.rs

@@ -230,11 +230,30 @@ impl<'hir> PathSegment<'hir> {
 
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
 pub struct ConstArg<'hir> {
-    pub value: &'hir AnonConst,
+    pub kind: ConstArgKind<'hir>,
     /// Indicates whether this comes from a `~const` desugaring.
     pub is_desugared_from_effects: bool,
 }
 
+impl<'hir> ConstArg<'hir> {
+    pub fn span(&self) -> Span {
+        match self.kind {
+            ConstArgKind::Anon(anon) => anon.span,
+        }
+    }
+
+    pub fn hir_id(&self) -> HirId {
+        match self.kind {
+            ConstArgKind::Anon(anon) => anon.hir_id,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, HashStable_Generic)]
+pub enum ConstArgKind<'hir> {
+    Anon(&'hir AnonConst),
+}
+
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
 pub struct InferArg {
     pub hir_id: HirId,
@@ -260,7 +279,7 @@ impl GenericArg<'_> {
         match self {
             GenericArg::Lifetime(l) => l.ident.span,
             GenericArg::Type(t) => t.span,
-            GenericArg::Const(c) => c.value.span,
+            GenericArg::Const(c) => c.span(),
             GenericArg::Infer(i) => i.span,
         }
     }
@@ -269,7 +288,7 @@ impl GenericArg<'_> {
         match self {
             GenericArg::Lifetime(l) => l.hir_id,
             GenericArg::Type(t) => t.hir_id,
-            GenericArg::Const(c) => c.value.hir_id,
+            GenericArg::Const(c) => c.hir_id(),
             GenericArg::Infer(i) => i.hir_id,
         }
     }

compiler/rustc_hir/src/intravisit.rs

@@ -344,6 +344,9 @@ pub trait Visitor<'v>: Sized {
     fn visit_anon_const(&mut self, c: &'v AnonConst) -> Self::Result {
         walk_anon_const(self, c)
     }
+    fn visit_const_arg(&mut self, c: &'v ConstArg) -> Self::Result {
+        walk_const_arg(self, c)
+    }
     fn visit_expr(&mut self, ex: &'v Expr<'v>) -> Self::Result {
         walk_expr(self, ex)
     }
@@ -716,6 +719,12 @@ pub fn walk_anon_const<'v, V: Visitor<'v>>(visitor: &mut V, constant: &'v AnonCo
     visitor.visit_nested_body(constant.body)
 }
 
+pub fn walk_const_arg<'v, V: Visitor<'v>>(visitor: &mut V, const_arg: &'v ConstArg) -> V::Result {
+    match const_arg.kind {
+        ConstArgKind::Anon(anon) => visitor.visit_anon_const(anon),
+    }
+}
+
 pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>) -> V::Result {
     try_visit!(visitor.visit_id(expression.hir_id));
     match expression.kind {
@@ -1203,7 +1212,7 @@ pub fn walk_generic_arg<'v, V: Visitor<'v>>(
     match generic_arg {
         GenericArg::Lifetime(lt) => visitor.visit_lifetime(lt),
         GenericArg::Type(ty) => visitor.visit_ty(ty),
-        GenericArg::Const(ct) => visitor.visit_anon_const(&ct.value),
+        GenericArg::Const(ct) => visitor.visit_const_arg(ct),
         GenericArg::Infer(inf) => visitor.visit_infer(inf),
     }
 }

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1594,7 +1594,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     i += 1;
                 }
                 GenericArg::Const(ct) => {
-                    self.visit_anon_const(&ct.value);
+                    self.visit_const_arg(ct);
                     i += 1;
                 }
                 GenericArg::Infer(inf) => {

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

@@ -8,10 +8,10 @@ use rustc_ast::ast::ParamKindOrd;
 use rustc_errors::{
     codes::*, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, MultiSpan,
 };
-use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::GenericArg;
+use rustc_hir::{self as hir, ConstArgKind};
 use rustc_middle::ty::{
     self, GenericArgsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty, TyCtxt,
 };
@@ -112,7 +112,8 @@ fn generic_arg_mismatch_err(
             }
         }
         (GenericArg::Const(cnst), GenericParamDefKind::Type { .. }) => {
-            let body = tcx.hir().body(cnst.value.body);
+            let ConstArgKind::Anon(anon) = cnst.kind;
+            let body = tcx.hir().body(anon.body);
             if let rustc_hir::ExprKind::Path(rustc_hir::QPath::Resolved(_, path)) = body.value.kind
             {
                 if let Res::Def(DefKind::Fn { .. }, id) = path.res {

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -31,10 +31,10 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_errors::{
     codes::*, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, FatalError,
 };
-use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{walk_generics, Visitor as _};
+use rustc_hir::{self as hir, ConstArgKind};
 use rustc_hir::{GenericArg, GenericArgs, HirId};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
@@ -479,11 +479,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
                         handle_ty_args(has_default, &inf.to_ty())
                     }
-                    (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
-                        let did = ct.value.def_id;
-                        tcx.feed_anon_const_type(did, tcx.type_of(param.def_id));
-                        ty::Const::from_anon_const(tcx, did).into()
-                    }
+                    (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => match &ct.kind {
+                        ConstArgKind::Anon(anon) => {
+                            let did = anon.def_id;
+                            tcx.feed_anon_const_type(did, tcx.type_of(param.def_id));
+                            ty::Const::from_anon_const(tcx, did).into()
+                        }
+                    },
                     (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
                         let ty = tcx
                             .at(self.span)

compiler/rustc_hir_pretty/src/lib.rs

@@ -8,7 +8,7 @@ use rustc_ast::util::parser::{self, AssocOp, Fixity};
 use rustc_ast_pretty::pp::Breaks::{Consistent, Inconsistent};
 use rustc_ast_pretty::pp::{self, Breaks};
 use rustc_ast_pretty::pprust::{Comments, PrintState};
-use rustc_hir as hir;
+use rustc_hir::{self as hir, ConstArgKind};
 use rustc_hir::{
     BindingMode, ByRef, GenericArg, GenericBound, GenericParam, GenericParamKind, HirId,
     LifetimeParamKind, Node, PatKind, RangeEnd, Term, TraitBoundModifier,
@@ -982,6 +982,12 @@ impl<'a> State<'a> {
         self.ann.nested(self, Nested::Body(constant.body))
     }
 
+    fn print_const_arg(&mut self, const_arg: &hir::ConstArg<'_>) {
+        match &const_arg.kind {
+            ConstArgKind::Anon(anon) => self.print_anon_const(anon),
+        }
+    }
+
     fn print_call_post(&mut self, args: &[hir::Expr<'_>]) {
         self.popen();
         self.commasep_exprs(Inconsistent, args);
@@ -1670,7 +1676,7 @@ impl<'a> State<'a> {
                             GenericArg::Lifetime(lt) if !elide_lifetimes => s.print_lifetime(lt),
                             GenericArg::Lifetime(_) => {}
                             GenericArg::Type(ty) => s.print_type(ty),
-                            GenericArg::Const(ct) => s.print_anon_const(&ct.value),
+                            GenericArg::Const(ct) => s.print_const_arg(ct),
                             GenericArg::Infer(_inf) => s.word("_"),
                         }
                     });

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -5,10 +5,10 @@ use crate::rvalue_scopes;
 use crate::{BreakableCtxt, Diverges, Expectation, FnCtxt, LoweredTy};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{Applicability, Diag, ErrorGuaranteed, MultiSpan, StashKey};
-use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
+use rustc_hir::{self as hir, ConstArg, ConstArgKind};
 use rustc_hir::{ExprKind, GenericArg, HirId, Node, QPath};
 use rustc_hir_analysis::hir_ty_lowering::errors::GenericsArgsErrExtend;
 use rustc_hir_analysis::hir_ty_lowering::generics::{
@@ -446,16 +446,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    pub fn lower_const_arg(&self, hir_ct: &hir::AnonConst, param_def_id: DefId) -> ty::Const<'tcx> {
-        let did = hir_ct.def_id;
-        self.tcx.feed_anon_const_type(did, self.tcx.type_of(param_def_id));
-        let ct = ty::Const::from_anon_const(self.tcx, did);
-        self.register_wf_obligation(
-            ct.into(),
-            self.tcx.hir().span(hir_ct.hir_id),
-            ObligationCauseCode::WellFormed(None),
-        );
-        ct
+    pub fn lower_const_arg(
+        &self,
+        const_arg: &ConstArg<'tcx>,
+        param_def_id: DefId,
+    ) -> ty::Const<'tcx> {
+        match &const_arg.kind {
+            ConstArgKind::Anon(anon) => {
+                let did = anon.def_id;
+                self.tcx.feed_anon_const_type(did, self.tcx.type_of(param_def_id));
+                let ct = ty::Const::from_anon_const(self.tcx, did);
+                self.register_wf_obligation(
+                    ct.into(),
+                    self.tcx.hir().span(anon.hir_id),
+                    ObligationCauseCode::WellFormed(None),
+                );
+                ct
+            }
+        }
     }
 
     // If the type given by the user has free regions, save it for later, since
@@ -1282,7 +1290,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.fcx.lower_ty(ty).raw.into()
                     }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
-                        self.fcx.lower_const_arg(&ct.value, param.def_id).into()
+                        self.fcx.lower_const_arg(ct, param.def_id).into()
                     }
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ty_infer(Some(param), inf.span).into()

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -394,7 +394,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                         self.cfcx.lower_ty(ty).raw.into()
                     }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
-                        self.cfcx.lower_const_arg(&ct.value, param.def_id).into()
+                        self.cfcx.lower_const_arg(ct, param.def_id).into()
                     }
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.cfcx.ty_infer(Some(param), inf.span).into()

compiler/rustc_lint/src/pass_by_value.rs

@@ -78,7 +78,7 @@ fn gen_args(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> String {
                     .tcx
                     .sess
                     .source_map()
-                    .span_to_snippet(c.value.span)
+                    .span_to_snippet(c.span())
                     .unwrap_or_else(|_| "_".into()),
                 GenericArg::Infer(_) => String::from("_"),
             })

compiler/rustc_passes/src/hir_stats.rs

@@ -452,7 +452,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
         match ga {
             hir::GenericArg::Lifetime(lt) => self.visit_lifetime(lt),
             hir::GenericArg::Type(ty) => self.visit_ty(ty),
-            hir::GenericArg::Const(ct) => self.visit_anon_const(&ct.value),
+            hir::GenericArg::Const(ct) => self.visit_const_arg(ct),
             hir::GenericArg::Infer(inf) => self.visit_infer(inf),
         }
     }

src/librustdoc/clean/mod.rs

@@ -36,10 +36,10 @@ use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_attr as attr;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet, IndexEntry};
 use rustc_errors::{codes::*, struct_span_code_err, FatalError};
-use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
 use rustc_hir::PredicateOrigin;
+use rustc_hir::{self as hir, ConstArgKind};
 use rustc_hir_analysis::lower_ty;
 use rustc_middle::metadata::Reexport;
 use rustc_middle::middle::resolve_bound_vars as rbv;
@@ -282,10 +282,16 @@ fn clean_lifetime<'tcx>(lifetime: &hir::Lifetime, cx: &mut DocContext<'tcx>) ->
 }
 
 pub(crate) fn clean_const<'tcx>(
-    constant: &hir::ConstArg<'_>,
+    constant: &hir::ConstArg<'tcx>,
     cx: &mut DocContext<'tcx>,
 ) -> Constant {
-    let def_id = cx.tcx.hir().body_owner_def_id(constant.value.body).to_def_id();
+    match &constant.kind {
+        ConstArgKind::Anon(anon) => clean_anon_const(anon, cx),
+    }
+}
+
+fn clean_anon_const<'tcx>(anon: &'tcx hir::AnonConst, cx: &mut DocContext<'tcx>) -> Constant {
+    let def_id = cx.tcx.hir().body_owner_def_id(anon.body).to_def_id();
     Constant {
         type_: Box::new(clean_middle_ty(
             ty::Binder::dummy(cx.tcx.type_of(def_id).instantiate_identity()),
@@ -294,7 +300,7 @@ pub(crate) fn clean_const<'tcx>(
             None,
         )),
         generics: Generics::default(),
-        kind: ConstantKind::Anonymous { body: constant.value.body },
+        kind: ConstantKind::Anonymous { body: anon.body },
     }
 }