Move const trait bounds checks to MIR constck

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -722,6 +722,32 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     }
                 };
 
+                // Check that all trait bounds that are marked as `~const` can be satisfied.
+                //
+                // 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();
+                let ocx = ObligationCtxt::new(&infcx);
+
+                let predicates = tcx.predicates_of(callee).instantiate(tcx, substs);
+                let cause = ObligationCause::new(
+                    terminator.source_info.span,
+                    self.body.source.def_id().expect_local(),
+                    ObligationCauseCode::ItemObligation(callee),
+                );
+                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);
+                }
+
                 // Attempting to call a trait method?
                 if let Some(trait_id) = tcx.trait_of_item(callee) {
                     trace!("attempting to call a trait method");
@@ -749,31 +775,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                         selcx.select(&obligation)
                     };
 
-                    // do a well-formedness check on the trait method being called. This is because typeck only does a
-                    // "non-const" check. This is required for correctness here.
-                    {
-                        let infcx = tcx.infer_ctxt().build();
-                        let ocx = ObligationCtxt::new(&infcx);
-
-                        let predicates = tcx.predicates_of(callee).instantiate(tcx, substs);
-                        let cause = ObligationCause::new(
-                            terminator.source_info.span,
-                            self.body.source.def_id().expect_local(),
-                            ObligationCauseCode::ItemObligation(callee),
-                        );
-                        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);
-                        }
-                    }
-
                     match implsrc {
                         Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
                             debug!(

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1416,41 +1416,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) {
         let param_env = self.param_env;
 
-        let remap = match self.tcx.def_kind(def_id) {
-            // Associated consts have `Self: ~const Trait` bounds that should be satisfiable when
-            // `Self: Trait` is satisfied because it does not matter whether the impl is `const`.
-            // Therefore we have to remap the param env here to be non-const.
-            hir::def::DefKind::AssocConst => true,
-            hir::def::DefKind::AssocFn
-                if self.tcx.def_kind(self.tcx.parent(def_id)) == hir::def::DefKind::Trait =>
-            {
-                // N.B.: All callsites to this function involve checking a path expression.
-                //
-                // When instantiating a trait method as a function item, it does not actually matter whether
-                // the trait is `const` or not, or whether `where T: ~const Tr` needs to be satisfied as
-                // `const`. If we were to introduce instantiating trait methods as `const fn`s, we would
-                // check that after this, either via a bound `where F: ~const FnOnce` or when coercing to a
-                // `const fn` pointer.
-                //
-                // FIXME(fee1-dead) FIXME(const_trait_impl): update this doc when trait methods can satisfy
-                // `~const FnOnce` or can be coerced to `const fn` pointer.
-                true
-            }
-            _ => false,
-        };
         let bounds = self.instantiate_bounds(span, def_id, &substs);
 
-        for mut obligation in traits::predicates_for_generics(
+        for obligation in traits::predicates_for_generics(
             |idx, predicate_span| {
                 traits::ObligationCause::new(span, self.body_id, code(idx, predicate_span))
             },
             param_env,
             bounds,
         ) {
-            if remap {
-                obligation = obligation.without_const(self.tcx);
-            }
-            self.register_predicate(obligation);
+            // N.B. We are remapping all predicates to non-const since we don't know if we just
+            // want them as function pointers or we are calling them from a const-context. The
+            // actual checking will occur in `rustc_const_eval::transform::check_consts`.
+            self.register_predicate(obligation.without_const(self.tcx));
         }
     }
 

tests/ui/const-generics/issue-93647.rs

@@ -1,6 +1,7 @@
 struct X<const N: usize = {
     (||1usize)()
     //~^ ERROR cannot call non-const closure
+    //~| ERROR the trait bound
 }>;
 
 fn main() {}

tests/ui/const-generics/issue-93647.stderr

@@ -1,3 +1,17 @@
+error[E0277]: the trait bound `[closure@$DIR/issue-93647.rs:2:6: 2:8]: Fn<()>` is not satisfied
+  --> $DIR/issue-93647.rs:2:5
+   |
+LL |     (||1usize)()
+   |     ^^^^^^^^^^^^ expected an `Fn<()>` closure, found `[closure@$DIR/issue-93647.rs:2:6: 2:8]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/issue-93647.rs:2:6: 2:8]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/issue-93647.rs:2:6: 2:8]`, but that implementation is not `const`
+  --> $DIR/issue-93647.rs:2:5
+   |
+LL |     (||1usize)()
+   |     ^^^^^^^^^^^^
+   = note: wrap the `[closure@$DIR/issue-93647.rs:2:6: 2:8]` in a closure with no arguments: `|| { /* code */ }`
+
 error[E0015]: cannot call non-const closure in constants
   --> $DIR/issue-93647.rs:2:5
    |
@@ -8,6 +22,7 @@ LL |     (||1usize)()
    = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
-error: aborting due to 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/consts/const-block-const-bound.stderr

@@ -1,44 +1,30 @@
 error[E0277]: can't drop `UnconstDrop` in const contexts
-  --> $DIR/const-block-const-bound.rs:20:11
+  --> $DIR/const-block-const-bound.rs:20:9
    |
 LL |         f(UnconstDrop);
-   |         - ^^^^^^^^^^^ the trait `~const Destruct` is not implemented for `UnconstDrop`
-   |         |
-   |         required by a bound introduced by this call
+   |         ^^^^^^^^^^^^^^ the trait `~const Destruct` is not implemented for `UnconstDrop`
    |
    = note: the trait bound `UnconstDrop: ~const Destruct` is not satisfied
-note: required by a bound in `f`
-  --> $DIR/const-block-const-bound.rs:6:15
-   |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |               ^^^^^^^^^^^^^^^ required by this bound in `f`
 help: consider borrowing here
    |
-LL |         f(&UnconstDrop);
-   |           +
-LL |         f(&mut UnconstDrop);
-   |           ++++
+LL |         &f(UnconstDrop);
+   |         +
+LL |         &mut f(UnconstDrop);
+   |         ++++
 
 error[E0277]: can't drop `NonDrop` in const contexts
-  --> $DIR/const-block-const-bound.rs:22:11
+  --> $DIR/const-block-const-bound.rs:22:9
    |
 LL |         f(NonDrop);
-   |         - ^^^^^^^ the trait `~const Destruct` is not implemented for `NonDrop`
-   |         |
-   |         required by a bound introduced by this call
+   |         ^^^^^^^^^^ the trait `~const Destruct` is not implemented for `NonDrop`
    |
    = note: the trait bound `NonDrop: ~const Destruct` is not satisfied
-note: required by a bound in `f`
-  --> $DIR/const-block-const-bound.rs:6:15
-   |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |               ^^^^^^^^^^^^^^^ required by this bound in `f`
 help: consider borrowing here
    |
-LL |         f(&NonDrop);
-   |           +
-LL |         f(&mut NonDrop);
-   |           ++++
+LL |         &f(NonDrop);
+   |         +
+LL |         &mut f(NonDrop);
+   |         ++++
 
 error: aborting due to 2 previous errors
 

tests/ui/consts/invalid-inline-const-in-match-arm.rs

@@ -5,5 +5,6 @@ fn main() {
     match () {
         const { (|| {})() } => {}
         //~^ ERROR cannot call non-const closure in constants
+        //~| ERROR the trait bound
     }
 }

tests/ui/consts/invalid-inline-const-in-match-arm.stderr

@@ -1,3 +1,17 @@
+error[E0277]: the trait bound `[closure@$DIR/invalid-inline-const-in-match-arm.rs:6:18: 6:20]: Fn<()>` is not satisfied
+  --> $DIR/invalid-inline-const-in-match-arm.rs:6:17
+   |
+LL |         const { (|| {})() } => {}
+   |                 ^^^^^^^^^ expected an `Fn<()>` closure, found `[closure@$DIR/invalid-inline-const-in-match-arm.rs:6:18: 6:20]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/invalid-inline-const-in-match-arm.rs:6:18: 6:20]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/invalid-inline-const-in-match-arm.rs:6:18: 6:20]`, but that implementation is not `const`
+  --> $DIR/invalid-inline-const-in-match-arm.rs:6:17
+   |
+LL |         const { (|| {})() } => {}
+   |                 ^^^^^^^^^
+   = note: wrap the `[closure@$DIR/invalid-inline-const-in-match-arm.rs:6:18: 6:20]` in a closure with no arguments: `|| { /* code */ }`
+
 error[E0015]: cannot call non-const closure in constants
   --> $DIR/invalid-inline-const-in-match-arm.rs:6:17
    |
@@ -8,6 +22,7 @@ LL |         const { (|| {})() } => {}
    = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
-error: aborting due to 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/consts/issue-28113.rs

@@ -3,6 +3,7 @@
 const X: u8 =
     || -> u8 { 5 }()
     //~^ ERROR cannot call non-const closure
+    //~| ERROR the trait bound
 ;
 
 fn main() {}

tests/ui/consts/issue-28113.stderr

@@ -1,3 +1,17 @@
+error[E0277]: the trait bound `[closure@$DIR/issue-28113.rs:4:5: 4:13]: Fn<()>` is not satisfied
+  --> $DIR/issue-28113.rs:4:5
+   |
+LL |     || -> u8 { 5 }()
+   |     ^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `[closure@$DIR/issue-28113.rs:4:5: 4:13]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/issue-28113.rs:4:5: 4:13]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/issue-28113.rs:4:5: 4:13]`, but that implementation is not `const`
+  --> $DIR/issue-28113.rs:4:5
+   |
+LL |     || -> u8 { 5 }()
+   |     ^^^^^^^^^^^^^^^^
+   = note: wrap the `[closure@$DIR/issue-28113.rs:4:5: 4:13]` in a closure with no arguments: `|| { /* code */ }`
+
 error[E0015]: cannot call non-const closure in constants
   --> $DIR/issue-28113.rs:4:5
    |
@@ -8,6 +22,7 @@ LL |     || -> u8 { 5 }()
    = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
-error: aborting due to 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/consts/issue-56164.rs

@@ -1,5 +1,6 @@
 const fn foo() { (||{})() }
 //~^ ERROR cannot call non-const closure
+//~| ERROR the trait bound
 
 const fn bad(input: fn()) {
     input()

tests/ui/consts/issue-56164.stderr

@@ -1,3 +1,17 @@
+error[E0277]: the trait bound `[closure@$DIR/issue-56164.rs:1:19: 1:21]: Fn<()>` is not satisfied
+  --> $DIR/issue-56164.rs:1:18
+   |
+LL | const fn foo() { (||{})() }
+   |                  ^^^^^^^^ expected an `Fn<()>` closure, found `[closure@$DIR/issue-56164.rs:1:19: 1:21]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/issue-56164.rs:1:19: 1:21]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/issue-56164.rs:1:19: 1:21]`, but that implementation is not `const`
+  --> $DIR/issue-56164.rs:1:18
+   |
+LL | const fn foo() { (||{})() }
+   |                  ^^^^^^^^
+   = note: wrap the `[closure@$DIR/issue-56164.rs:1:19: 1:21]` in a closure with no arguments: `|| { /* code */ }`
+
 error[E0015]: cannot call non-const closure in constant functions
   --> $DIR/issue-56164.rs:1:18
    |
@@ -9,7 +23,7 @@ LL | const fn foo() { (||{})() }
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
 error: function pointer calls are not allowed in constant functions
-  --> $DIR/issue-56164.rs:5:5
+  --> $DIR/issue-56164.rs:6:5
    |
 LL |     input()
    |     ^^^^^^^
@@ -26,6 +40,7 @@ note: erroneous constant used
 LL | const fn foo() { (||{})() }
    |                  ^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 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/consts/issue-68542-closure-in-array-len.rs

@@ -4,6 +4,7 @@
 
 struct Bug {
     a: [(); (|| { 0 })()] //~ ERROR cannot call non-const closure
+    //~^ ERROR the trait bound
 }
 
 fn main() {}

tests/ui/consts/issue-68542-closure-in-array-len.stderr

@@ -1,3 +1,17 @@
+error[E0277]: the trait bound `[closure@$DIR/issue-68542-closure-in-array-len.rs:6:14: 6:16]: Fn<()>` is not satisfied
+  --> $DIR/issue-68542-closure-in-array-len.rs:6:13
+   |
+LL |     a: [(); (|| { 0 })()]
+   |             ^^^^^^^^^^^^ expected an `Fn<()>` closure, found `[closure@$DIR/issue-68542-closure-in-array-len.rs:6:14: 6:16]`
+   |
+   = help: the trait `~const Fn<()>` is not implemented for closure `[closure@$DIR/issue-68542-closure-in-array-len.rs:6:14: 6:16]`
+note: the trait `Fn<()>` is implemented for `[closure@$DIR/issue-68542-closure-in-array-len.rs:6:14: 6:16]`, but that implementation is not `const`
+  --> $DIR/issue-68542-closure-in-array-len.rs:6:13
+   |
+LL |     a: [(); (|| { 0 })()]
+   |             ^^^^^^^^^^^^
+   = note: wrap the `[closure@$DIR/issue-68542-closure-in-array-len.rs:6:14: 6:16]` in a closure with no arguments: `|| { /* code */ }`
+
 error[E0015]: cannot call non-const closure in constants
   --> $DIR/issue-68542-closure-in-array-len.rs:6:13
    |
@@ -8,6 +22,7 @@ LL |     a: [(); (|| { 0 })()]
    = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
-error: aborting due to 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/never_type/issue-52443.rs

@@ -11,4 +11,5 @@ fn main() {
     //~| ERROR cannot convert
     //~| ERROR mutable references
     //~| ERROR cannot call
+    //~| ERROR the trait bound
 }

tests/ui/never_type/issue-52443.stderr

@@ -58,6 +58,19 @@ LL |     [(); { for _ in 0usize.. {}; 0}];
    = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
    = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
 
+error[E0277]: the trait bound `RangeFrom<usize>: Iterator` is not satisfied
+  --> $DIR/issue-52443.rs:9:21
+   |
+LL |     [(); { for _ in 0usize.. {}; 0}];
+   |                     ^^^^^^^^ `RangeFrom<usize>` is not an iterator
+   |
+   = help: the trait `~const Iterator` is not implemented for `RangeFrom<usize>`
+note: the trait `Iterator` is implemented for `RangeFrom<usize>`, but that implementation is not `const`
+  --> $DIR/issue-52443.rs:9:21
+   |
+LL |     [(); { for _ in 0usize.. {}; 0}];
+   |                     ^^^^^^^^
+
 error[E0015]: cannot call non-const fn `<RangeFrom<usize> as Iterator>::next` in constants
   --> $DIR/issue-52443.rs:9:21
    |
@@ -67,7 +80,7 @@ LL |     [(); { for _ in 0usize.. {}; 0}];
    = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
 
-error: aborting due to 6 previous errors; 1 warning emitted
+error: aborting due to 7 previous errors; 1 warning emitted
 
-Some errors have detailed explanations: E0015, E0308, E0658.
+Some errors have detailed explanations: E0015, E0277, E0308, E0658.
 For more information about an error, try `rustc --explain E0015`.