Partially implement ConstArgHasType

Author: BoxyUwU

compiler/rustc_infer/src/infer/relate/combine.rs

@@ -22,11 +22,10 @@ use super::glb::Glb;
 use super::lub::Lub;
 use super::type_relating::TypeRelating;
 use super::StructurallyRelateAliases;
-use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, TypeTrace};
+use crate::infer::{DefineOpaqueTypes, InferCtxt, TypeTrace};
 use crate::traits::{Obligation, PredicateObligations};
 use rustc_middle::bug;
 use rustc_middle::infer::unify_key::EffectVarValue;
-use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::relate::{RelateResult, TypeRelation};
 use rustc_middle::ty::{self, InferConst, Ty, TyCtxt, TypeVisitableExt, Upcast};
@@ -159,12 +158,6 @@ impl<'tcx> InferCtxt<'tcx> {
         let a = self.shallow_resolve_const(a);
         let b = self.shallow_resolve_const(b);
 
-        // It is always an error if the types of two constants that are related are not equal.
-        let InferOk { value: (), obligations } = self
-            .at(&ObligationCause::dummy_with_span(relation.span()), relation.param_env())
-            .eq(DefineOpaqueTypes::No, a.ty(), b.ty())?;
-        relation.register_obligations(obligations);
-
         match (a.kind(), b.kind()) {
             (
                 ty::ConstKind::Infer(InferConst::Var(a_vid)),

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -2685,6 +2685,22 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     .with_span_label(span, format!("cannot satisfy `{predicate}`"))
                 }
             }
+
+            // Given some `ConstArgHasType(?x, usize)`, we should not emit an error such as
+            // "type annotations needed: cannot satisfy the constant `_` has type `usize`"
+            // Instead we should emit a normal error suggesting the user to turbofish the
+            // const parameter that is currently being inferred. Unfortunately we cannot
+            // nicely emit such an error so we delay an ICE incase nobody else reports it
+            // for us.
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                return self.tcx.sess.dcx().span_delayed_bug(
+                    span,
+                    format!(
+                        "`ambiguous ConstArgHasType({:?}, {:?}) unaccompanied by inference error`",
+                        ct, ty
+                    ),
+                );
+            }
             _ => {
                 if let Some(e) = self.tainted_by_errors() {
                     return e;

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -429,16 +429,43 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 // This is because this is not ever a useful obligation to report
                 // as the cause of an overflow.
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                    match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
-                        // Only really excercised by generic_const_exprs
-                        DefineOpaqueTypes::Yes,
-                        ct.ty(),
-                        ty,
-                    ) {
-                        Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
-                        Err(_) => ProcessResult::Error(FulfillmentErrorCode::Select(
-                            SelectionError::Unimplemented,
-                        )),
+                    // FIXME(BoxyUwU): Really we should not be calling `ct.ty()` for any variant
+                    // other than `ConstKind::Value`. Unfortunately this would require looking in the
+                    // env for any `ConstArgHasType` assumptions for parameters and placeholders. I
+                    // don't really want to implement this in the old solver so I haven't.
+                    //
+                    // We do still stall on infer vars though as otherwise a goal like:
+                    // `ConstArgHasType(?x: usize, usize)` can succeed even though it might later
+                    // get unified with some const that is not of type `usize`.
+                    match ct.kind() {
+                        ty::ConstKind::Infer(inf) => {
+                            pending_obligation.stalled_on.clear();
+                            let var = match inf {
+                                ty::InferConst::Var(vid) => TyOrConstInferVar::Const(vid),
+                                ty::InferConst::EffectVar(vid) => TyOrConstInferVar::Effect(vid),
+                                ty::InferConst::Fresh(_) => {
+                                    bug!("encountered fresh {:?} in fulfill", ct)
+                                }
+                            };
+                            pending_obligation.stalled_on.extend([var]);
+                            ProcessResult::Unchanged
+                        }
+                        ty::ConstKind::Error(_) => return ProcessResult::Changed(vec![]),
+                        _ => {
+                            match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
+                                // Only really excercised by generic_const_exprs
+                                DefineOpaqueTypes::Yes,
+                                ct.ty(),
+                                ty,
+                            ) {
+                                Ok(inf_ok) => {
+                                    ProcessResult::Changed(mk_pending(inf_ok.into_obligations()))
+                                }
+                                Err(_) => ProcessResult::Error(FulfillmentErrorCode::Select(
+                                    SelectionError::Unimplemented,
+                                )),
+                            }
+                        }
                     }
                 }
 

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -992,10 +992,24 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
                 ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                    // FIXME(BoxyUwU): Really we should not be calling `ct.ty()` for any variant
+                    // other than `ConstKind::Value`. Unfortunately this would require looking in the
+                    // env for any `ConstArgHasType` assumptions for parameters and placeholders. I
+                    // don't really want to implement this in the old solver so I haven't.
+                    //
+                    // We do still stall on infer vars though as otherwise a goal like:
+                    // `ConstArgHasType(?x: usize, usize)` can succeed even though it might later
+                    // get unified with some const that is not of type `usize`.
+                    let ct_ty = match ct.kind() {
+                        ty::ConstKind::Infer(_) => return Ok(EvaluatedToAmbig),
+                        ty::ConstKind::Error(_) => return Ok(EvaluatedToOk),
+                        _ => ct.ty(),
+                    };
+
                     match self.infcx.at(&obligation.cause, obligation.param_env).eq(
                         // Only really excercised by generic_const_exprs
                         DefineOpaqueTypes::Yes,
-                        ct.ty(),
+                        ct_ty,
                         ty,
                     ) {
                         Ok(inf_ok) => self.evaluate_predicates_recursively(

tests/ui/consts/eval_type_mismatch.rs renamed to tests/crashes/121858.rs

@@ -1,17 +1,14 @@
+//@ known-bug: #121858
 #![feature(generic_const_exprs)]
-#![allow(incomplete_features)]
 
 struct Outer<const A: i64, const B: usize>();
 impl<const A: usize, const B: usize> Outer<A, B>
-//~^ ERROR: `A` is not of type `i64`
-//~| ERROR: mismatched types
 where
     [(); A + (B * 2)]:,
 {
-    fn o() {}
+    fn o() -> Union {}
 }
 
 fn main() {
     Outer::<1, 1>::o();
-    //~^ ERROR: no function or associated item named `o` found
 }

tests/ui/coherence/negative-coherence/generic_const_type_mismatch.rs

@@ -8,5 +8,6 @@ impl<const N: u8> Trait for [(); N] {}
 //~^ ERROR: mismatched types
 impl<const N: i8> Trait for [(); N] {}
 //~^ ERROR: mismatched types
+//~| ERROR: conflicting implementations of trait `Trait`
 
 fn main() {}

tests/ui/coherence/negative-coherence/generic_const_type_mismatch.stderr

@@ -1,3 +1,12 @@
+error[E0119]: conflicting implementations of trait `Trait` for type `[(); _]`
+  --> $DIR/generic_const_type_mismatch.rs:9:1
+   |
+LL | impl<const N: u8> Trait for [(); N] {}
+   | ----------------------------------- first implementation here
+LL |
+LL | impl<const N: i8> Trait for [(); N] {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[(); _]`
+
 error[E0308]: mismatched types
   --> $DIR/generic_const_type_mismatch.rs:7:34
    |
@@ -10,6 +19,7 @@ error[E0308]: mismatched types
 LL | impl<const N: i8> Trait for [(); N] {}
    |                                  ^ expected `usize`, found `i8`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0119, E0308.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/const-generics/bad-subst-const-kind.rs

@@ -10,5 +10,7 @@ impl<const N: u64> Q for [u8; N] {
     const ASSOC: usize = 1;
 }
 
-pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-//~^ ERROR: `[u8; 13]: Q` is not satisfied
+pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] {
+    //~^ ERROR: the constant `13` is not of type `u64`
+    todo!()
+}

tests/ui/const-generics/bad-subst-const-kind.stderr

@@ -1,10 +1,16 @@
-error[E0277]: the trait bound `[u8; 13]: Q` is not satisfied
+error: the constant `13` is not of type `u64`
   --> $DIR/bad-subst-const-kind.rs:13:24
    |
-LL | pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-   |                        ^^^^^^^^ the trait `Q` is not implemented for `[u8; 13]`
+LL | pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] {
+   |                        ^^^^^^^^ expected `u64`, found `usize`
    |
-   = help: the trait `Q` is implemented for `[u8; N]`
+note: required for `[u8; 13]` to implement `Q`
+  --> $DIR/bad-subst-const-kind.rs:8:20
+   |
+LL | impl<const N: u64> Q for [u8; N] {
+   |      ------------  ^     ^^^^^^^
+   |      |
+   |      unsatisfied trait bound introduced here
 
 error[E0308]: mismatched types
   --> $DIR/bad-subst-const-kind.rs:8:31
@@ -14,5 +20,4 @@ LL | impl<const N: u64> Q for [u8; N] {
 
 error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0277, E0308.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0308`.

tests/ui/const-generics/defaults/doesnt_infer.rs

@@ -3,7 +3,9 @@
 struct Foo<const N: u32 = 2>;
 
 impl<const N: u32> Foo<N> {
-    fn foo() -> Self { loop {} }
+    fn foo() -> Self {
+        loop {}
+    }
 }
 
 fn main() {