Address code review comments

compiler/rustc_ty_utils/src/consts.rs

@@ -1,84 +1,77 @@
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_target::abi::VariantIdx;
 
-/// Tries to destructure constants of type Array or Adt into the constants
+use std::iter;
+
+/// Tries to destructure array, ADT or tuple constants into the constants
 /// of its fields.
 pub(crate) fn destructure_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     const_: ty::Const<'tcx>,
 ) -> ty::DestructuredConst<'tcx> {
-    if let ty::ConstKind::Value(valtree) = const_.kind() {
-        let branches = match valtree {
-            ty::ValTree::Branch(b) => b,
-            _ => bug!("cannot destructure constant {:?}", const_),
-        };
+    let ty::ConstKind::Value(valtree) = const_.kind() else {
+        bug!("cannot destructure constant {:?}", const_)
+    };
 
-        let (fields, variant) = match const_.ty().kind() {
-            ty::Array(inner_ty, _) | ty::Slice(inner_ty) => {
-                // construct the consts for the elements of the array/slice
-                let field_consts = branches
-                    .iter()
-                    .map(|b| {
-                        tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Value(*b), ty: *inner_ty })
-                    })
-                    .collect::<Vec<_>>();
-                debug!(?field_consts);
+    let branches = match valtree {
+        ty::ValTree::Branch(b) => b,
+        _ => bug!("cannot destructure constant {:?}", const_),
+    };
 
-                (field_consts, None)
-            }
-            ty::Adt(def, _) if def.variants().is_empty() => bug!("unreachable"),
-            ty::Adt(def, substs) => {
-                let variant_idx = if def.is_enum() {
-                    VariantIdx::from_u32(branches[0].unwrap_leaf().try_to_u32().unwrap())
-                } else {
-                    VariantIdx::from_u32(0)
-                };
-                let fields = &def.variant(variant_idx).fields;
-                let mut field_consts = Vec::with_capacity(fields.len());
+    let (fields, variant) = match const_.ty().kind() {
+        ty::Array(inner_ty, _) | ty::Slice(inner_ty) => {
+            // construct the consts for the elements of the array/slice
+            let field_consts = branches
+                .iter()
+                .map(|b| tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Value(*b), ty: *inner_ty }))
+                .collect::<Vec<_>>();
+            debug!(?field_consts);
 
-                // Note: First element inValTree corresponds to variant of enum
-                let mut valtree_idx = if def.is_enum() { 1 } else { 0 };
-                for field in fields {
-                    let field_ty = field.ty(tcx, substs);
-                    let field_valtree = branches[valtree_idx]; // first element of branches is variant
-                    let field_const = tcx.mk_const(ty::ConstS {
-                        kind: ty::ConstKind::Value(field_valtree),
-                        ty: field_ty,
-                    });
-                    field_consts.push(field_const);
-                    valtree_idx += 1;
-                }
-                debug!(?field_consts);
+            (field_consts, None)
+        }
+        ty::Adt(def, _) if def.variants().is_empty() => bug!("unreachable"),
+        ty::Adt(def, substs) => {
+            let (variant_idx, branches) = if def.is_enum() {
+                let (head, rest) = branches.split_first().unwrap();
+                (VariantIdx::from_u32(head.unwrap_leaf().try_to_u32().unwrap()), rest)
+            } else {
+                (VariantIdx::from_u32(0), branches)
+            };
+            let fields = &def.variant(variant_idx).fields;
+            let mut field_consts = Vec::with_capacity(fields.len());
 
-                (field_consts, Some(variant_idx))
+            for (field, field_valtree) in iter::zip(fields, branches) {
+                let field_ty = field.ty(tcx, substs);
+                let field_const = tcx.mk_const(ty::ConstS {
+                    kind: ty::ConstKind::Value(*field_valtree),
+                    ty: field_ty,
+                });
+                field_consts.push(field_const);
             }
-            ty::Tuple(elem_tys) => {
-                let fields = elem_tys
-                    .iter()
-                    .enumerate()
-                    .map(|(i, elem_ty)| {
-                        let elem_valtree = branches[i];
-                        tcx.mk_const(ty::ConstS {
-                            kind: ty::ConstKind::Value(elem_valtree),
-                            ty: elem_ty,
-                        })
+            debug!(?field_consts);
+
+            (field_consts, Some(variant_idx))
+        }
+        ty::Tuple(elem_tys) => {
+            let fields = iter::zip(*elem_tys, branches)
+                .map(|(elem_ty, elem_valtree)| {
+                    tcx.mk_const(ty::ConstS {
+                        kind: ty::ConstKind::Value(*elem_valtree),
+                        ty: elem_ty,
                     })
-                    .collect::<Vec<_>>();
+                })
+                .collect::<Vec<_>>();
 
-                (fields, None)
-            }
-            _ => bug!("cannot destructure constant {:?}", const_),
-        };
+            (fields, None)
+        }
+        _ => bug!("cannot destructure constant {:?}", const_),
+    };
 
-        let fields = tcx.arena.alloc_from_iter(fields.into_iter());
+    let fields = tcx.arena.alloc_from_iter(fields.into_iter());
 
-        ty::DestructuredConst { variant, fields }
-    } else {
-        bug!("cannot destructure constant {:?}", const_)
-    }
+    ty::DestructuredConst { variant, fields }
 }
 
 pub fn provide(providers: &mut ty::query::Providers) {
-    *providers =
-        ty::query::Providers { destructure_const, ..*providers };
+    *providers = ty::query::Providers { destructure_const, ..*providers };
 }

src/test/ui/const-generics/issue-66451.rs

@@ -17,7 +17,7 @@ fn main() {
         Foo {
             value: 3,
             nested: &Bar(4),
-        }  
+        }
     }> = Test;
     let y: Test<{
         Foo {