Fix warning and intrinsics stability gate

Author: celinval

compiler/rustc_ast_lowering/src/expr.rs

@@ -401,11 +401,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         cond_hir_id: HirId,
     ) -> &'hir hir::Expr<'hir> {
         let cond_fn = self.expr_ident(span, cond_ident, cond_hir_id);
-        let span = self.mark_span_with_reason(DesugaringKind::Contract, span, None);
         let call_expr = self.expr_call_lang_item_fn_mut(
             span,
             hir::LangItem::ContractCheckEnsures,
-            arena_vec![self; *expr, *cond_fn],
+            arena_vec![self; *cond_fn, *expr],
         );
         self.arena.alloc(call_expr)
     }

compiler/rustc_ast_lowering/src/item.rs

@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use rustc_abi::ExternAbi;
 use rustc_ast::ptr::P;
 use rustc_ast::visit::AssocCtxt;
@@ -1209,8 +1211,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let precond = if let Some(req) = &contract.requires {
                     // Lower the precondition check intrinsic.
                     let lowered_req = this.lower_expr_mut(&req);
+                    let req_span = this.mark_span_with_reason(
+                        DesugaringKind::Contract,
+                        lowered_req.span,
+                        Some(Arc::clone(&this.allow_contract_internals)),
+                    );
                     let precond = this.expr_call_lang_item_fn_mut(
-                        req.span,
+                        req_span,
                         hir::LangItem::ContractCheckRequires,
                         &*arena_vec![this; lowered_req],
                     );
@@ -1220,6 +1227,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 };
                 let (postcond, body) = if let Some(ens) = &contract.ensures {
                     let ens_span = this.lower_span(ens.span);
+                    let ens_span = this.mark_span_with_reason(
+                        DesugaringKind::Contract,
+                        ens_span,
+                        Some(Arc::clone(&this.allow_contract_internals)),
+                    );
                     // Set up the postcondition `let` statement.
                     let check_ident: Ident =
                         Ident::from_str_and_span("__ensures_checker", ens_span);

compiler/rustc_ast_lowering/src/lib.rs

@@ -143,6 +143,7 @@ struct LoweringContext<'a, 'hir> {
     allow_async_iterator: Arc<[Symbol]>,
     allow_for_await: Arc<[Symbol]>,
     allow_async_fn_traits: Arc<[Symbol]>,
+    allow_contract_internals: Arc<[Symbol]>,
 
     attribute_parser: AttributeParser<'hir>,
 }
@@ -191,6 +192,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // FIXME(gen_blocks): how does `closure_track_caller`/`async_fn_track_caller`
             // interact with `gen`/`async gen` blocks
             allow_async_iterator: [sym::gen_future, sym::async_iterator].into(),
+            allow_contract_internals: [sym::contracts_internals].into(),
 
             attribute_parser: AttributeParser::new(tcx.sess, tcx.features(), registered_tools),
         }

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -283,7 +283,10 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
                 safe_to_expose_on_stable,
                 is_function_call,
                 gate_already_checked,
-            } if gate_already_checked || self.tcx.features().enabled(gate) => {
+            } if gate_already_checked
+                || self.tcx.features().enabled(gate)
+                || span.allows_unstable(gate) =>
+            {
                 if gate_already_checked {
                     assert!(
                         !safe_to_expose_on_stable,

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -236,7 +236,7 @@ pub fn check_intrinsic_type(
         // where C: for<'a> Fn(&'a Ret) -> bool,
         //
         // so: two type params, 0 lifetime param, 0 const params, two inputs, no return
-        (2, 0, 0, vec![param(0), param(1)], param(0), hir::Safety::Safe)
+        (2, 0, 0, vec![param(0), param(1)], param(1), hir::Safety::Safe)
     } else {
         let safety = intrinsic_operation_unsafety(tcx, intrinsic_id);
         let (n_tps, n_cts, inputs, output) = match intrinsic_name {

library/core/src/contracts.rs

@@ -2,15 +2,16 @@
 
 pub use crate::macros::builtin::{contracts_ensures as ensures, contracts_requires as requires};
 
-/// Emitted by rustc as a desugaring of `#[ensures(PRED)] fn foo() -> R { ... [return R;] ... }`
-/// into: `fn foo() { let _check = build_check_ensures(|ret| PRED) ... [return _check(R);] ... }`
-/// (including the implicit return of the tail expression, if any).
+/// This is an identity function used as part of the desugaring of the `#[ensures]` attribute.
 ///
-/// This call helps with type inference for the predicate.
+/// This is an existing hack to allow users to omit the type of the return value in their ensures
+/// attribute.
+///
+/// Ideally, rustc should be able to generate the type annotation.
+/// The existing lowering logic makes it rather hard to add the explicit type annotation,
+/// while the function call is fairly straight forward.
 #[unstable(feature = "contracts_internals", issue = "128044" /* compiler-team#759 */)]
-#[rustc_const_unstable(feature = "contracts", issue = "128044")]
 #[lang = "contract_build_check_ensures"]
-#[track_caller]
 pub const fn build_check_ensures<Ret, C>(cond: C) -> C
 where
     C: Fn(&Ret) -> bool + Copy + 'static,

library/core/src/intrinsics/mod.rs

@@ -3453,7 +3453,7 @@ pub const fn contract_checks() -> bool {
 ///
 /// Note that this function is a no-op during constant evaluation.
 #[unstable(feature = "contracts_internals", issue = "128044")]
-#[rustc_const_unstable(feature = "contracts", issue = "128044")]
+#[rustc_const_unstable(feature = "contracts_internals", issue = "128044")]
 #[lang = "contract_check_requires"]
 #[rustc_intrinsic]
 pub const fn contract_check_requires<C: Fn() -> bool + Copy>(cond: C) {
@@ -3478,12 +3478,12 @@ pub const fn contract_check_requires<C: Fn() -> bool + Copy>(cond: C) {
 /// Note that this function is a no-op during constant evaluation.
 #[cfg(not(bootstrap))]
 #[unstable(feature = "contracts_internals", issue = "128044")]
-#[rustc_const_unstable(feature = "contracts", issue = "128044")]
+#[rustc_const_unstable(feature = "contracts_internals", issue = "128044")]
 #[lang = "contract_check_ensures"]
 #[rustc_intrinsic]
-pub const fn contract_check_ensures<Ret, C: Fn(&Ret) -> bool + Copy>(ret: Ret, cond: C) -> Ret {
+pub const fn contract_check_ensures<C: Fn(&Ret) -> bool + Copy, Ret>(cond: C, ret: Ret) -> Ret {
     const_eval_select!(
-        @capture[Ret, C: Fn(&Ret) -> bool + Copy] { ret: Ret, cond: C } -> Ret :
+        @capture[C: Fn(&Ret) -> bool + Copy, Ret] { cond: C, ret: Ret } -> Ret :
         if const {
             // Do nothing
             ret

tests/ui/contracts/contract-attributes-nest.chk_pass.stderr

@@ -7,16 +7,5 @@ LL | #![feature(contracts)]
    = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-warning: unreachable expression
-  --> $DIR/contract-attributes-nest.rs:23:1
-   |
-LL | #[core::contracts::ensures(|ret| *ret > 100)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unreachable expression
-...
-LL |         return x.baz + 50;
-   |         ----------------- any code following this expression is unreachable
-   |
-   = note: `#[warn(unreachable_code)]` on by default
-
-warning: 2 warnings emitted
+warning: 1 warning emitted
 

tests/ui/contracts/contract-attributes-nest.rs

@@ -21,7 +21,6 @@
 
 #[core::contracts::requires(x.baz > 0)]
 #[core::contracts::ensures(|ret| *ret > 100)]
-//~^ WARN unreachable expression [unreachable_code]
 fn nest(x: Baz) -> i32
 {
     loop {

tests/ui/contracts/contract-attributes-nest.unchk_fail_post.stderr

@@ -7,16 +7,5 @@ LL | #![feature(contracts)]
    = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-warning: unreachable expression
-  --> $DIR/contract-attributes-nest.rs:23:1
-   |
-LL | #[core::contracts::ensures(|ret| *ret > 100)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unreachable expression
-...
-LL |         return x.baz + 50;
-   |         ----------------- any code following this expression is unreachable
-   |
-   = note: `#[warn(unreachable_code)]` on by default
-
-warning: 2 warnings emitted
+warning: 1 warning emitted