Improve contracts intrisics and remove wrapper function

1. Document the new intrinsics.
2. Make the intrinsics actually check the contract if enabled, and
   remove `contract::check_requires` function.
3. Use panic with no unwind in case contract is using to check for
   safety, we probably don't want to unwind. Following the same
   reasoning as UB checks.

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -222,17 +222,15 @@ pub fn check_intrinsic_type(
         };
         (n_tps, 0, 0, inputs, output, hir::Safety::Unsafe)
     } else if intrinsic_name == sym::contract_check_ensures {
-        // contract_check_ensures::<'a, Ret, C>(&'a Ret, C) -> bool
+        // contract_check_ensures::<'a, Ret, C>(&'a Ret, C)
         // where C: impl Fn(&'a Ret) -> bool,
         //
-        // so: two type params, one lifetime param, 0 const params, two inputs, returns boolean
+        // so: two type params, one lifetime param, 0 const params, two inputs, no return
 
         let p = generics.param_at(0, tcx);
         let r = ty::Region::new_early_param(tcx, p.to_early_bound_region_data());
         let ref_ret = Ty::new_imm_ref(tcx, r, param(1));
-        // let br = ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BrAnon };
-        // let ref_ret = Ty::new_imm_ref(tcx, ty::Region::new_bound(tcx, ty::INNERMOST, br), param(0));
-        (2, 1, 0, vec![ref_ret, param(2)], tcx.types.bool, hir::Safety::Safe)
+        (2, 1, 0, vec![ref_ret, param(2)], tcx.types.unit, hir::Safety::Safe)
     } else {
         let safety = intrinsic_operation_unsafety(tcx, intrinsic_id);
         let (n_tps, n_cts, inputs, output) = match intrinsic_name {
@@ -627,7 +625,7 @@ pub fn check_intrinsic_type(
             // contract_checks() -> bool
             sym::contract_checks => (0, 0, Vec::new(), tcx.types.bool),
             // contract_check_requires::<C>(C) -> bool, where C: impl Fn() -> bool
-            sym::contract_check_requires => (1, 0, vec![param(0)], tcx.types.bool),
+            sym::contract_check_requires => (1, 0, vec![param(0)], tcx.types.unit),
 
             sym::simd_eq
             | sym::simd_ne

library/core/src/contracts.rs

@@ -1,38 +1,21 @@
 //! Unstable module containing the unstable contracts lang items and attribute macros.
+#![cfg(not(bootstrap))]
 
-#[cfg(not(bootstrap))]
-pub use crate::macros::builtin::contracts_ensures as ensures;
-#[cfg(not(bootstrap))]
-pub use crate::macros::builtin::contracts_requires as requires;
-
-/// Emitted by rustc as a desugaring of `#[requires(PRED)] fn foo(x: X) { ... }`
-/// into: `fn foo(x: X) { check_requires(|| PRED) ... }`
-#[cfg(not(bootstrap))]
-#[unstable(feature = "rustc_contracts_internals", issue = "133866" /* compiler-team#759 */)]
-#[lang = "contract_check_requires"]
-#[track_caller]
-pub fn check_requires<C: FnOnce() -> bool>(c: C) {
-    if core::intrinsics::contract_checks() {
-        assert!(core::intrinsics::contract_check_requires(c), "failed requires check");
-    }
-}
+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).
-#[cfg(not(bootstrap))]
 #[unstable(feature = "rustc_contracts_internals", issue = "133866" /* compiler-team#759 */)]
 #[lang = "contract_build_check_ensures"]
 #[track_caller]
-pub fn build_check_ensures<Ret, C>(c: C) -> impl (FnOnce(Ret) -> Ret) + Copy
+pub fn build_check_ensures<Ret, C>(cond: C) -> impl (Fn(Ret) -> Ret) + Copy
 where
-    C: for<'a> FnOnce(&'a Ret) -> bool + Copy + 'static,
+    C: for<'a> Fn(&'a Ret) -> bool + Copy + 'static,
 {
     #[track_caller]
     move |ret| {
-        if core::intrinsics::contract_checks() {
-            assert!(core::intrinsics::contract_check_ensures(&ret, c), "failed ensures check");
-        }
+        crate::intrinsics::contract_check_ensures(&ret, cond);
         ret
     }
 }

library/core/src/intrinsics/mod.rs

@@ -4057,18 +4057,32 @@ pub const fn contract_checks() -> bool {
     false
 }
 
+/// Check if the pre-condition `cond` has been met.
+///
+/// By default, if `contract_checks` is enabled, this will panic with no unwind if the condition
+/// returns false.
 #[cfg(not(bootstrap))]
 #[unstable(feature = "rustc_contracts_internals", issue = "133866" /* compiler-team#759 */)]
+#[lang = "contract_check_requires"]
 #[rustc_intrinsic]
-pub fn contract_check_requires<C: FnOnce() -> bool>(c: C) -> bool {
-    c()
+pub fn contract_check_requires<C: Fn() -> bool>(cond: C) {
+    if contract_checks() && !cond() {
+        // Emit no unwind panic in case this was a safety requirement.
+        crate::panicking::panic_nounwind("failed requires check");
+    }
 }
 
+/// Check if the post-condition `cond` has been met.
+///
+/// By default, if `contract_checks` is enabled, this will panic with no unwind if the condition
+/// returns false.
 #[cfg(not(bootstrap))]
 #[unstable(feature = "rustc_contracts_internals", issue = "133866" /* compiler-team#759 */)]
 #[rustc_intrinsic]
-pub fn contract_check_ensures<'a, Ret, C: FnOnce(&'a Ret) -> bool>(ret: &'a Ret, c: C) -> bool {
-    c(ret)
+pub fn contract_check_ensures<'a, Ret, C: Fn(&'a Ret) -> bool>(ret: &'a Ret, cond: C) {
+    if contract_checks() && !cond(ret) {
+        crate::panicking::panic_nounwind("failed ensures check");
+    }
 }
 
 /// The intrinsic will return the size stored in that vtable.

tests/ui/contracts/internal_machinery/contract-intrinsics.rs

@@ -1,23 +1,36 @@
-//@ run-pass
-//@ revisions: yes no none
-//@ [yes] compile-flags: -Zcontract-checks=yes
-//@ [no] compile-flags: -Zcontract-checks=no
+//@ revisions: default unchk_pass chk_pass chk_fail_ensures chk_fail_requires
+//
+//@ [default] run-pass
+//@ [unchk_pass] run-pass
+//@ [chk_pass] run-pass
+//@ [chk_fail_requires] run-fail
+//@ [chk_fail_ensures] run-fail
+//
+//@ [unchk_pass] compile-flags: -Zcontract-checks=no
+//@ [chk_pass] compile-flags: -Zcontract-checks=yes
+//@ [chk_fail_requires] compile-flags: -Zcontract-checks=yes
+//@ [chk_fail_ensures] compile-flags: -Zcontract-checks=yes
 #![feature(cfg_contract_checks, rustc_contracts_internals, core_intrinsics)]
 
 fn main() {
-    #[cfg(none)] // default: disabled
+    #[cfg(any(default, unchk_pass))] // default: disabled
     assert_eq!(core::intrinsics::contract_checks(), false);
 
-    #[cfg(yes)] // explicitly enabled
+    #[cfg(chk_pass)] // explicitly enabled
     assert_eq!(core::intrinsics::contract_checks(), true);
 
-    #[cfg(no)] // explicitly disabled
-    assert_eq!(core::intrinsics::contract_checks(), false);
+    // always pass
+    core::intrinsics::contract_check_requires(|| true);
 
-    assert_eq!(core::intrinsics::contract_check_requires(|| true), true);
-    assert_eq!(core::intrinsics::contract_check_requires(|| false), false);
+    // fail if enabled
+    #[cfg(any(default, unchk_pass, chk_fail_requires))]
+    core::intrinsics::contract_check_requires(|| false);
 
     let doubles_to_two = { let old = 2; move |ret| ret + ret == old };
-    assert_eq!(core::intrinsics::contract_check_ensures(&1, doubles_to_two), true);
-    assert_eq!(core::intrinsics::contract_check_ensures(&2, doubles_to_two), false);
+    // Always pass
+    core::intrinsics::contract_check_ensures(&1, doubles_to_two);
+
+    // Fail if enabled
+    #[cfg(any(default, unchk_pass, chk_fail_ensures))]
+    core::intrinsics::contract_check_ensures(&2, doubles_to_two);
 }

tests/ui/contracts/internal_machinery/contract-lang-items.rs

@@ -1,27 +1,21 @@
-//@ revisions: unchk_pass unchk_fail_pre unchk_fail_post chk_pass chk_fail_pre chk_fail_post
+//@ revisions: unchk_pass unchk_fail_post chk_pass chk_fail_post
 //
 //@ [unchk_pass] run-pass
-//@ [unchk_fail_pre] run-pass
 //@ [unchk_fail_post] run-pass
 //@ [chk_pass] run-pass
 //
-//@ [chk_fail_pre] run-fail
 //@ [chk_fail_post] run-fail
 //
 //@ [unchk_pass] compile-flags: -Zcontract-checks=no
-//@ [unchk_fail_pre] compile-flags: -Zcontract-checks=no
 //@ [unchk_fail_post] compile-flags: -Zcontract-checks=no
 //
 //@ [chk_pass] compile-flags: -Zcontract-checks=yes
-//@ [chk_fail_pre] compile-flags: -Zcontract-checks=yes
 //@ [chk_fail_post] compile-flags: -Zcontract-checks=yes
 
 #![feature(rustc_contracts)] // to access core::contracts
 #![feature(rustc_contracts_internals)] // to access check_requires lang item
 
 fn foo(x: Baz) -> i32 {
-    core::contracts::check_requires(|| x.baz > 0);
-
     let injected_checker = {
         core::contracts::build_check_ensures(|ret| *ret > 100)
     };
@@ -36,13 +30,9 @@ struct Baz { baz: i32 }
 const BAZ_PASS_PRE_POST: Baz = Baz { baz: 100 };
 #[cfg(any(unchk_fail_post, chk_fail_post))]
 const BAZ_FAIL_POST: Baz = Baz { baz: 10 };
-#[cfg(any(unchk_fail_pre, chk_fail_pre))]
-const BAZ_FAIL_PRE: Baz = Baz { baz: -10 };
 
 fn main() {
     assert_eq!(foo(BAZ_PASS_PRE_POST), 150);
-    #[cfg(any(unchk_fail_pre, chk_fail_pre))]
-    foo(BAZ_FAIL_PRE);
     #[cfg(any(unchk_fail_post, chk_fail_post))]
     foo(BAZ_FAIL_POST);
 }

tests/ui/contracts/internal_machinery/internal-feature-gating.rs

@@ -9,9 +9,6 @@ fn main() {
     core::intrinsics::contract_check_ensures(&1, |_|true);
     //~^ ERROR use of unstable library feature `rustc_contracts_internals`
 
-    // lang items are guarded by rustc_contracts_internals feature gate.
-    core::contracts::check_requires(|| true);
-    //~^ ERROR use of unstable library feature `rustc_contracts_internals`
     core::contracts::build_check_ensures(|_: &()| true);
     //~^ ERROR use of unstable library feature `rustc_contracts_internals`
 

tests/ui/contracts/internal_machinery/internal-feature-gating.stderr

@@ -1,5 +1,5 @@
 error[E0658]: contract internal machinery is for internal use only
-  --> $DIR/internal-feature-gating.rs:19:51
+  --> $DIR/internal-feature-gating.rs:16:51
    |
 LL |     fn identity_1() -> i32 rustc_contract_requires(|| true) { 10 }
    |                                                   ^^^^^^^^^
@@ -9,7 +9,7 @@ LL |     fn identity_1() -> i32 rustc_contract_requires(|| true) { 10 }
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: contract internal machinery is for internal use only
-  --> $DIR/internal-feature-gating.rs:21:50
+  --> $DIR/internal-feature-gating.rs:18:50
    |
 LL |     fn identity_2() -> i32 rustc_contract_ensures(|_| true) { 10 }
    |                                                  ^^^^^^^^^^
@@ -49,17 +49,7 @@ LL |     core::intrinsics::contract_check_ensures(&1, |_|true);
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: use of unstable library feature `rustc_contracts_internals`
-  --> $DIR/internal-feature-gating.rs:13:5
-   |
-LL |     core::contracts::check_requires(|| true);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #133866 <https://github.com/rust-lang/rust/issues/133866> for more information
-   = help: add `#![feature(rustc_contracts_internals)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: use of unstable library feature `rustc_contracts_internals`
-  --> $DIR/internal-feature-gating.rs:15:5
+  --> $DIR/internal-feature-gating.rs:12:5
    |
 LL |     core::contracts::build_check_ensures(|_: &()| true);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -68,6 +58,6 @@ LL |     core::contracts::build_check_ensures(|_: &()| true);
    = help: add `#![feature(rustc_contracts_internals)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 7 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0658`.