Completely deny calling functions with const conditions in MIR const check unless const_trait_impl is enabled

This will help us make sure that we never leak any conditionally const
functions into stable.

Author: compiler-errors

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -363,7 +363,7 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
     }
 
     fn revalidate_conditional_constness(
-        &self,
+        &mut self,
         callee: DefId,
         callee_args: ty::GenericArgsRef<'tcx>,
         call_source: CallSource,
@@ -374,11 +374,24 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
             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(TypingMode::from_param_env(self.param_env));
         let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
 
-        let const_conditions = tcx.const_conditions(callee).instantiate(tcx, callee_args);
-
         let body_id = self.body.source.def_id().expect_local();
         let host_polarity = match self.const_kind() {
             hir::ConstContext::ConstFn => ty::HostPolarity::Maybe,
@@ -621,7 +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);
 
@@ -639,12 +651,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     }
                 };
 
-                self.revalidate_conditional_constness(
-                    callee,
-                    fn_args,
-                    call_source,
-                    terminator.source_info.span,
-                );
+                self.revalidate_conditional_constness(callee, fn_args, call_source, *fn_span);
 
                 let mut is_trait = false;
                 // Attempting to call a trait method?
@@ -684,7 +691,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             None
                         };
                         self.check_op(ops::FnCallNonConst {
-                            caller,
                             callee,
                             args: fn_args,
                             span: *fn_span,
@@ -774,7 +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 ConstCx { tcx, param_env, body, .. } = *ccx;
+        let FnCallNonConst { callee, args, span, call_source, feature } = *self;
+        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);
@@ -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
-    //[stocknc,gatednc]~^^ ERROR: the trait bound
+    //[stocknc]~| ERROR: cannot call
+    //[gatednc]~^^^ ERROR: the trait bound
     Const.func();
-    //[stock]~^ ERROR: cannot call
-    //[stocknc]~^^ ERROR: cannot call
+    //[stock,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

@@ -1,8 +1,14 @@
-error[E0277]: the trait bound `cross_crate::NonConst: ~const cross_crate::MyTrait` is not satisfied
-  --> $DIR/cross-crate.rs:19:5
+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
+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
@@ -11,24 +17,37 @@ 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:23:11
+   |
+LL |     Const.func();
+   |           ^^^^^^
+   |
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
 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();
    |           ^^^^^^
    |
    = 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 3 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0015, E0277.
-For more information about an error, try `rustc --explain E0015`.
+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/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`.