Auto merge of #132276 - compiler-errors:enforce-fx-in-mir, r=fee1-dead

Double-check conditional constness in MIR

To prevent any unchecked `~const` bounds from leaking through during MIR lowering.

If this check fails, it will eventually just delay a bug, but for now it reports errors. That error reporting may be redundant if we're calling it from code that already doesn't allow `~const` (i.e. when the `effects` and `const_trait_impl` gates are disabled), but I don't think it's that big of a deal.

edit: This also makes sure that we issue a const stability error if we encounter *any* function with const conditions when `const_trait_impl` is not enabled. This ensures that that feature remains airtight.

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -11,7 +11,6 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, LangItem};
 use rustc_index::bit_set::BitSet;
 use rustc_infer::infer::TyCtxtInferExt;
-use rustc_infer::traits::ObligationCause;
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
@@ -20,9 +19,11 @@ use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TypeVisitableExt};
 use rustc_mir_dataflow::Analysis;
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
-use rustc_span::{DUMMY_SP, Span, Symbol, sym};
+use rustc_span::{Span, Symbol, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
-use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt};
+use rustc_trait_selection::traits::{
+    Obligation, ObligationCause, ObligationCauseCode, ObligationCtxt,
+};
 use tracing::{debug, instrument, trace};
 
 use super::ops::{self, NonConstOp, Status};
@@ -360,6 +361,73 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
         // end of evaluation.
         !is_transient
     }
+
+    fn revalidate_conditional_constness(
+        &mut self,
+        callee: DefId,
+        callee_args: ty::GenericArgsRef<'tcx>,
+        call_source: CallSource,
+        call_span: Span,
+    ) {
+        let tcx = self.tcx;
+        if !tcx.is_conditionally_const(callee) {
+            return;
+        }
+
+        let const_conditions = tcx.const_conditions(callee).instantiate(tcx, callee_args);
+        // If there are any const conditions on this fn and `const_trait_impl`
+        // is not enabled, simply bail. We shouldn't be able to call conditionally
+        // const functions on stable.
+        if !const_conditions.is_empty() && !tcx.features().const_trait_impl() {
+            self.check_op(ops::FnCallNonConst {
+                callee,
+                args: callee_args,
+                span: call_span,
+                call_source,
+                feature: Some(sym::const_trait_impl),
+            });
+            return;
+        }
+
+        let infcx = tcx.infer_ctxt().build(self.body.typing_mode(tcx));
+        let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
+
+        let body_id = self.body.source.def_id().expect_local();
+        let host_polarity = match self.const_kind() {
+            hir::ConstContext::ConstFn => ty::BoundConstness::Maybe,
+            hir::ConstContext::Static(_) | hir::ConstContext::Const { .. } => {
+                ty::BoundConstness::Const
+            }
+        };
+        let const_conditions = ocx.normalize(
+            &ObligationCause::misc(call_span, body_id),
+            self.param_env,
+            const_conditions,
+        );
+        ocx.register_obligations(const_conditions.into_iter().map(|(trait_ref, span)| {
+            Obligation::new(
+                tcx,
+                ObligationCause::new(
+                    call_span,
+                    body_id,
+                    ObligationCauseCode::WhereClause(callee, span),
+                ),
+                self.param_env,
+                trait_ref.to_host_effect_clause(tcx, host_polarity),
+            )
+        }));
+
+        let errors = ocx.select_all_or_error();
+        if !errors.is_empty() {
+            // FIXME(effects): Soon this should be unconditionally delaying a bug.
+            if matches!(call_source, CallSource::Normal) && tcx.features().effects() {
+                tcx.dcx()
+                    .span_delayed_bug(call_span, "this should have reported a ~const error in HIR");
+            } else {
+                infcx.err_ctxt().report_fulfillment_errors(errors);
+            }
+        }
+    }
 }
 
 impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
@@ -566,7 +634,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 };
 
                 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
-                let caller = self.def_id();
 
                 let fn_ty = func.ty(body, tcx);
 
@@ -584,31 +651,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     }
                 };
 
-                // Check that all trait bounds that are marked as `~const` can be satisfied.
+                self.revalidate_conditional_constness(callee, fn_args, call_source, *fn_span);
-                //
-                // Typeck only does a "non-const" check since it operates on HIR and cannot distinguish
-                // which path expressions are getting called on and which path expressions are only used
-                // as function pointers. This is required for correctness.
-                let infcx = tcx.infer_ctxt().build(body.typing_mode(tcx));
-                let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
-
-                let predicates = tcx.predicates_of(callee).instantiate(tcx, fn_args);
-                let cause = ObligationCause::new(
-                    terminator.source_info.span,
-                    self.body.source.def_id().expect_local(),
-                    ObligationCauseCode::WhereClause(callee, DUMMY_SP),
-                );
-                let normalized_predicates = ocx.normalize(&cause, param_env, predicates);
-                ocx.register_obligations(traits::predicates_for_generics(
-                    |_, _| cause.clone(),
-                    self.param_env,
-                    normalized_predicates,
-                ));
-
-                let errors = ocx.select_all_or_error();
-                if !errors.is_empty() {
-                    infcx.err_ctxt().report_fulfillment_errors(errors);
-                }
 
                 let mut is_trait = false;
                 // Attempting to call a trait method?
@@ -648,7 +691,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             None
                         };
                         self.check_op(ops::FnCallNonConst {
-                            caller,
                             callee,
                             args: fn_args,
                             span: *fn_span,
@@ -738,7 +780,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 // Trait functions are not `const fn` so we have to skip them here.
                 if !tcx.is_const_fn(callee) && !is_trait {
                     self.check_op(ops::FnCallNonConst {
-                        caller,
                         callee,
                         args: fn_args,
                         span: *fn_span,

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -1,6 +1,5 @@
 //! Concrete error types for all operations which may be invalid in a certain const context.
 
-use hir::def_id::LocalDefId;
 use hir::{ConstContext, LangItem};
 use rustc_errors::Diag;
 use rustc_errors::codes::*;
@@ -74,7 +73,6 @@ impl<'tcx> NonConstOp<'tcx> for FnCallIndirect {
 /// A function call where the callee is not marked as `const`.
 #[derive(Debug, Clone, Copy)]
 pub(crate) struct FnCallNonConst<'tcx> {
-    pub caller: LocalDefId,
     pub callee: DefId,
     pub args: GenericArgsRef<'tcx>,
     pub span: Span,
@@ -87,8 +85,9 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
     #[allow(rustc::diagnostic_outside_of_impl)]
     #[allow(rustc::untranslatable_diagnostic)]
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, _: Span) -> Diag<'tcx> {
-        let FnCallNonConst { caller, callee, args, span, call_source, feature } = *self;
+        let FnCallNonConst { callee, args, span, call_source, feature } = *self;
-        let ConstCx { tcx, param_env, body, .. } = *ccx;
+        let ConstCx { tcx, param_env, .. } = *ccx;
+        let caller = ccx.def_id();
 
         let diag_trait = |err, self_ty: Ty<'_>, trait_id| {
             let trait_ref = TraitRef::from_method(tcx, trait_id, args);
@@ -116,7 +115,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                     let obligation =
                         Obligation::new(tcx, ObligationCause::dummy(), param_env, trait_ref);
 
-                    let infcx = tcx.infer_ctxt().build(body.typing_mode(tcx));
+                    let infcx = tcx.infer_ctxt().build(ccx.body.typing_mode(tcx));
                     let mut selcx = SelectionContext::new(&infcx);
                     let implsrc = selcx.select(&obligation);
 
@@ -289,7 +288,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
         if let Some(feature) = feature {
             ccx.tcx.disabled_nightly_features(
                 &mut err,
-                body.source.def_id().as_local().map(|local| ccx.tcx.local_def_id_to_hir_id(local)),
+                Some(ccx.tcx.local_def_id_to_hir_id(caller)),
                 [(String::new(), feature)],
             );
         }

tests/ui/traits/const-traits/const-drop-fail-2.stderr

@@ -29,6 +29,12 @@ LL | const fn check<T: ~const Destruct>(_: T) {}
    |                                    |
    |                                    the destructor for this type cannot be evaluated in constant functions
 
+error[E0277]: the trait bound `T: ~const A` is not satisfied
+  --> $DIR/const-drop-fail-2.rs:41:9
+   |
+LL |         T::a();
+   |         ^^^^^^
+
 error[E0015]: cannot call non-const fn `<T as A>::a` in constant functions
   --> $DIR/const-drop-fail-2.rs:41:9
    |
@@ -41,7 +47,7 @@ help: add `#![feature(effects)]` to the crate attributes to enable
 LL + #![feature(effects)]
    |
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
-Some errors have detailed explanations: E0015, E0493.
+Some errors have detailed explanations: E0015, E0277, E0493.
 For more information about an error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/const-drop.precise.stderr

@@ -78,6 +78,12 @@ error[E0493]: destructor of `T` cannot be evaluated at compile-time
 LL | const fn a<T: ~const Destruct>(_: T) {}
    |                                ^ the destructor for this type cannot be evaluated in constant functions
 
+error[E0277]: the trait bound `T: ~const SomeTrait` is not satisfied
+  --> $DIR/const-drop.rs:69:13
+   |
+LL |             T::foo();
+   |             ^^^^^^^^
+
 error[E0015]: cannot call non-const fn `<T as SomeTrait>::foo` in constant functions
   --> $DIR/const-drop.rs:69:13
    |
@@ -90,7 +96,7 @@ help: add `#![feature(effects)]` to the crate attributes to enable
 LL + #![feature(effects)]
    |
 
-error: aborting due to 10 previous errors
+error: aborting due to 11 previous errors
 
 Some errors have detailed explanations: E0015, E0277, E0493.
 For more information about an error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/const-drop.stock.stderr

@@ -80,6 +80,12 @@ LL | const fn a<T: ~const Destruct>(_: T) {}
    |                                |
    |                                the destructor for this type cannot be evaluated in constant functions
 
+error[E0277]: the trait bound `T: ~const SomeTrait` is not satisfied
+  --> $DIR/const-drop.rs:69:13
+   |
+LL |             T::foo();
+   |             ^^^^^^^^
+
 error[E0015]: cannot call non-const fn `<T as SomeTrait>::foo` in constant functions
   --> $DIR/const-drop.rs:69:13
    |
@@ -92,7 +98,7 @@ help: add `#![feature(effects)]` to the crate attributes to enable
 LL + #![feature(effects)]
    |
 
-error: aborting due to 10 previous errors
+error: aborting due to 11 previous errors
 
 Some errors have detailed explanations: E0015, E0277, E0493.
 For more information about an error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/cross-crate.rs

@@ -18,10 +18,11 @@ const fn const_context() {
     #[cfg(any(stocknc, gatednc))]
     NonConst.func();
     //[stocknc]~^ ERROR: cannot call
-    //[gatednc]~^^ ERROR: the trait bound
+    //[stocknc]~| ERROR: cannot call
+    //[gatednc]~^^^ ERROR: the trait bound
     Const.func();
-    //[stock]~^ ERROR: cannot call
+    //[stock,stocknc]~^ ERROR: cannot call
-    //[stocknc]~^^ ERROR: cannot call
+    //[stock,stocknc]~| ERROR: cannot call
 }
 
 fn main() {}

tests/ui/traits/const-traits/cross-crate.stock.stderr

@@ -1,5 +1,5 @@
 error[E0015]: cannot call non-const fn `<cross_crate::Const as cross_crate::MyTrait>::func` in constant functions
-  --> $DIR/cross-crate.rs:22:11
+  --> $DIR/cross-crate.rs:23:11
    |
 LL |     Const.func();
    |           ^^^^^^
@@ -10,6 +10,19 @@ help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 LL + #![feature(const_trait_impl)]
    |
 
-error: aborting due to 1 previous error
+error[E0015]: cannot call non-const fn `<cross_crate::Const as cross_crate::MyTrait>::func` in constant functions
+  --> $DIR/cross-crate.rs:23:11
+   |
+LL |     Const.func();
+   |           ^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
+   |
+LL + #![feature(const_trait_impl)]
+   |
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/cross-crate.stocknc.stderr

@@ -10,8 +10,21 @@ help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 LL + #![feature(const_trait_impl)]
    |
 
+error[E0015]: cannot call non-const fn `<cross_crate::NonConst as cross_crate::MyTrait>::func` in constant functions
+  --> $DIR/cross-crate.rs:19:14
+   |
+LL |     NonConst.func();
+   |              ^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
+   |
+LL + #![feature(const_trait_impl)]
+   |
+
 error[E0015]: cannot call non-const fn `<cross_crate::Const as cross_crate::MyTrait>::func` in constant functions
-  --> $DIR/cross-crate.rs:22:11
+  --> $DIR/cross-crate.rs:23:11
    |
 LL |     Const.func();
    |           ^^^^^^
@@ -22,6 +35,19 @@ help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 LL + #![feature(const_trait_impl)]
    |
 
-error: aborting due to 2 previous errors
+error[E0015]: cannot call non-const fn `<cross_crate::Const as cross_crate::MyTrait>::func` in constant functions
+  --> $DIR/cross-crate.rs:23:11
+   |
+LL |     Const.func();
+   |           ^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
+   |
+LL + #![feature(const_trait_impl)]
+   |
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/default-method-body-is-const-body-checking.rs

@@ -1,6 +1,3 @@
-//@ known-bug: #110395
-//@ check-pass
-
 #![feature(const_trait_impl)]
 
 #[const_trait]
@@ -13,7 +10,7 @@ const fn foo<T>() where T: ~const Tr {}
 pub trait Foo {
     fn foo() {
         foo::<()>();
-        //FIXME ~^ ERROR the trait bound `(): Tr` is not satisfied
+        //~^ ERROR the trait bound `(): ~const Tr` is not satisfied
     }
 }
 

tests/ui/traits/const-traits/default-method-body-is-const-body-checking.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `(): ~const Tr` is not satisfied
+  --> $DIR/default-method-body-is-const-body-checking.rs:12:9
+   |
+LL |         foo::<()>();
+   |         ^^^^^^^^^^^
+   |
+note: required by a bound in `foo`
+  --> $DIR/default-method-body-is-const-body-checking.rs:7:28
+   |
+LL | const fn foo<T>() where T: ~const Tr {}
+   |                            ^^^^^^ required by this bound in `foo`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/const-traits/specializing-constness-2.stderr

@@ -1,3 +1,9 @@
+error[E0277]: the trait bound `T: ~const A` is not satisfied
+  --> $DIR/specializing-constness-2.rs:27:5
+   |
+LL |     <T as A>::a();
+   |     ^^^^^^^^^^^^^
+
 error[E0015]: cannot call non-const fn `<T as A>::a` in constant functions
   --> $DIR/specializing-constness-2.rs:27:5
    |
@@ -10,6 +16,7 @@ help: add `#![feature(effects)]` to the crate attributes to enable
 LL + #![feature(effects)]
    |
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0015`.
+Some errors have detailed explanations: E0015, E0277.
+For more information about an error, try `rustc --explain E0015`.

tests/ui/traits/const-traits/staged-api-user-crate.rs

@@ -11,6 +11,7 @@ fn non_const_context() {
 const fn stable_const_context() {
     Unstable::func();
     //~^ ERROR cannot call non-const fn `<staged_api::Unstable as staged_api::MyTrait>::func` in constant functions
+    //~| ERROR cannot call non-const fn `<staged_api::Unstable as staged_api::MyTrait>::func` in constant functions
 }
 
 fn main() {}

tests/ui/traits/const-traits/staged-api-user-crate.stderr

@@ -10,6 +10,19 @@ help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 LL + #![feature(const_trait_impl)]
    |
 
-error: aborting due to 1 previous error
+error[E0015]: cannot call non-const fn `<staged_api::Unstable as staged_api::MyTrait>::func` in constant functions
+  --> $DIR/staged-api-user-crate.rs:12:5
+   |
+LL |     Unstable::func();
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
+   |
+LL + #![feature(const_trait_impl)]
+   |
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0015`.