Auto merge of #77124 - spastorino:const-exprs-rfc-2920, r=oli-obk

Implement const expressions and patterns (RFC 2920)

cc `@ecstatic-morse` `@lcnr` `@oli-obk` `@petrochenkov`

compiler/rustc_typeck/src/check/expr.rs

@@ -286,6 +286,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
             ExprKind::DropTemps(ref e) => self.check_expr_with_expectation(e, expected),
             ExprKind::Array(ref args) => self.check_expr_array(args, expected, expr),
+            ExprKind::ConstBlock(ref anon_const) => self.to_const(anon_const).ty,
             ExprKind::Repeat(ref element, ref count) => {
                 self.check_expr_repeat(element, count, expected, expr)
             }

compiler/rustc_typeck/src/check/mod.rs

@@ -111,6 +111,7 @@ use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::{HirIdMap, Node};
 use rustc_index::bit_set::BitSet;
 use rustc_index::vec::Idx;
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::GenericArgKind;
@@ -528,7 +529,20 @@ fn typeck_with_fallback<'tcx>(
                     hir::TyKind::Infer => Some(AstConv::ast_ty_to_ty(&fcx, ty)),
                     _ => None,
                 })
-                .unwrap_or_else(fallback);
+                .unwrap_or_else(|| match tcx.hir().get(id) {
+                    Node::AnonConst(_) => match tcx.hir().get(tcx.hir().get_parent_node(id)) {
+                        Node::Expr(&hir::Expr {
+                            kind: hir::ExprKind::ConstBlock(ref anon_const),
+                            ..
+                        }) if anon_const.hir_id == id => fcx.next_ty_var(TypeVariableOrigin {
+                            kind: TypeVariableOriginKind::TypeInference,
+                            span,
+                        }),
+                        _ => fallback(),
+                    },
+                    _ => fallback(),
+                });
+
             let expected_type = fcx.normalize_associated_types_in(body.value.span, &expected_type);
             fcx.require_type_is_sized(expected_type, body.value.span, traits::ConstSized);
 

compiler/rustc_typeck/src/collect/type_of.rs

@@ -309,6 +309,12 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     tcx.types.usize
                 }
 
+                Node::Expr(&Expr { kind: ExprKind::ConstBlock(ref anon_const), .. })
+                    if anon_const.hir_id == hir_id =>
+                {
+                    tcx.typeck(def_id).node_type(anon_const.hir_id)
+                }
+
                 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => tcx
                     .adt_def(tcx.hir().get_parent_did(hir_id).to_def_id())
                     .repr

compiler/rustc_typeck/src/expr_use_visitor.rs

@@ -258,7 +258,10 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
                 self.consume_exprs(&ia.inputs_exprs);
             }
 
-            hir::ExprKind::Continue(..) | hir::ExprKind::Lit(..) | hir::ExprKind::Err => {}
+            hir::ExprKind::Continue(..)
+            | hir::ExprKind::Lit(..)
+            | hir::ExprKind::ConstBlock(..)
+            | hir::ExprKind::Err => {}
 
             hir::ExprKind::Loop(ref blk, _, _) => {
                 self.walk_block(blk);

compiler/rustc_typeck/src/mem_categorization.rs

@@ -370,6 +370,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
             | hir::ExprKind::Loop(..)
             | hir::ExprKind::Match(..)
             | hir::ExprKind::Lit(..)
+            | hir::ExprKind::ConstBlock(..)
             | hir::ExprKind::Break(..)
             | hir::ExprKind::Continue(..)
             | hir::ExprKind::Struct(..)