Enable contracts for const functions

Use `const_eval_select!()` macro to enable contract checking only at
runtime. The existing contract logic relies on closures,
which are not supported in constant functions.

This commit also removes one level of indirection for ensures clauses,
however, it currently has a spurious warning message when the bottom
of the function is unreachable.

1 files changed, 9 insertions, 4 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 80bb1e8fc41..0b7a7630431 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -397,12 +397,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         expr: &'hir hir::Expr<'hir>,
         span: Span,
-        check_ident: Ident,
-        check_hir_id: HirId,
+        cond_ident: Ident,
+        cond_hir_id: HirId,
     ) -> &'hir hir::Expr<'hir> {
-        let checker_fn = self.expr_ident(span, check_ident, check_hir_id);
+        let cond_fn = self.expr_ident(span, cond_ident, cond_hir_id);
         let span = self.mark_span_with_reason(DesugaringKind::Contract, span, None);
-        self.expr_call(span, checker_fn, std::slice::from_ref(expr))
+        let call_expr = self.expr_call_lang_item_fn_mut(
+            span,
+            hir::LangItem::ContractCheckEnsures,
+            arena_vec![self; *expr, *cond_fn],
+        );
+        self.arena.alloc(call_expr)
     }
 
     pub(crate) fn lower_const_block(&mut self, c: &AnonConst) -> hir::ConstBlock {