[WIP] discard impl candidates before evaluating

compiler/rustc_error_codes/src/error_codes/E0275.md

@@ -8,6 +8,12 @@ trait Foo {}
 struct Bar<T>(T);
 
 impl<T> Foo for T where Bar<T>: Foo {}
+
+fn takes_foo<T: Foo>() {}
+
+fn calls_takes_foo() {
+    takes_foo::<()>();
+}
 ```
 
 This error occurs when there was a recursive trait requirement that overflowed

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

@@ -157,17 +157,33 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         // Winnow, but record the exact outcome of evaluation, which
         // is needed for specialization. Propagate overflow if it occurs.
+        let mut eval_cand = |c| match self.evaluate_candidate(stack, &c) {
+            Ok(eval) if eval.may_apply() => {
+                Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
+            }
+            Ok(_) => Ok(None),
+            Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
+            Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
+            Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
+        };
+
+        // this is very not perf and should be fixed xd
+        let drop_impl_candidates = candidates
+            .iter()
+            .filter(|c| matches!(c, SelectionCandidate::ParamCandidate(_)))
+            .cloned()
+            .map(&mut eval_cand)
+            .flat_map(Result::transpose)
+            .try_fold(false, |should_drop, param_candidate| {
+                let cand = &param_candidate?.candidate;
+                Ok::<_, SelectionError<'_>>(
+                    should_drop || !(cand.is_global() && !cand.has_late_bound_regions()),
+                )
+            })?;
         let mut candidates = candidates
             .into_iter()
-            .map(|c| match self.evaluate_candidate(stack, &c) {
-                Ok(eval) if eval.may_apply() => {
-                    Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
-                }
-                Ok(_) => Ok(None),
-                Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
-                Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
-                Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
-            })
+            .filter(|c| !matches!(c, SelectionCandidate::ImplCandidate(_) if drop_impl_candidates))
+            .map(&mut eval_cand)
             .flat_map(Result::transpose)
             .collect::<Result<Vec<_>, _>>()?;
 

src/test/ui/const-generics/issues/issue-90318.rs

@@ -13,15 +13,13 @@ fn consume<T: 'static>(_val: T)
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
     //~^ ERROR: overly complex generic constant
-    //~| ERROR: cannot call non-const operator in constants
 {
 }
 
 fn test<T: 'static>()
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
     //~^ ERROR: overly complex generic constant
-    //~| ERROR: cannot call non-const operator in constants
 {
 }
 

src/test/ui/const-generics/issues/issue-90318.stderr

@@ -9,22 +9,8 @@ LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
    = help: consider moving this anonymous constant into a `const` function
    = note: this operation may be supported in the future
 
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/issue-90318.rs:14:10
-   |
-LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: impl defined here, but it is not `const`
-  --> $SRC_DIR/core/src/any.rs:LL:COL
-   |
-LL | #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
-   |                       ^^^^^^^^^
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
-   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error: overly complex generic constant
-  --> $DIR/issue-90318.rs:22:8
+  --> $DIR/issue-90318.rs:21:8
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
    |        ^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
@@ -34,20 +20,5 @@ LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
    = help: consider moving this anonymous constant into a `const` function
    = note: this operation may be supported in the future
 
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/issue-90318.rs:22:10
-   |
-LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: impl defined here, but it is not `const`
-  --> $SRC_DIR/core/src/any.rs:LL:COL
-   |
-LL | #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
-   |                       ^^^^^^^^^
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
-   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0015`.

src/test/ui/error-codes/E0275.rs

@@ -2,7 +2,10 @@ trait Foo {}
 
 struct Bar<T>(T);
 
-impl<T> Foo for T where Bar<T>: Foo {} //~ ERROR E0275
+impl<T> Foo for T where Bar<T>: Foo {}
+
+fn takes_foo<T: Foo>() {}
 
 fn main() {
+    takes_foo::<()>(); //~ ERROR E0275
 }

src/test/ui/error-codes/E0275.stderr

@@ -1,17 +1,22 @@
-error[E0275]: overflow evaluating the requirement `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>: Foo`
-  --> $DIR/E0275.rs:5:33
+error[E0275]: overflow evaluating the requirement `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<()>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>: Foo`
+  --> $DIR/E0275.rs:10:5
    |
-LL | impl<T> Foo for T where Bar<T>: Foo {}
-   |                                 ^^^
+LL |     takes_foo::<()>();
+   |     ^^^^^^^^^^^^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`E0275`)
-note: required because of the requirements on the impl of `Foo` for `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
+note: required because of the requirements on the impl of `Foo` for `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<()>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
   --> $DIR/E0275.rs:5:9
    |
 LL | impl<T> Foo for T where Bar<T>: Foo {}
    |         ^^^     ^
    = note: 127 redundant requirements hidden
-   = note: required because of the requirements on the impl of `Foo` for `Bar<T>`
+   = note: required because of the requirements on the impl of `Foo` for `()`
+note: required by a bound in `takes_foo`
+  --> $DIR/E0275.rs:7:17
+   |
+LL | fn takes_foo<T: Foo>() {}
+   |                 ^^^ required by this bound in `takes_foo`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-20413.rs

@@ -6,8 +6,6 @@ struct NoData<T>;
 //~^ ERROR: parameter `T` is never used
 
 impl<T> Foo for T where NoData<T>: Foo {
-  //~^ ERROR: overflow evaluating the requirement
-  //~| ERROR: overflow evaluating the requirement
   fn answer(self) {
     let val: NoData<T> = NoData;
   }
@@ -26,16 +24,12 @@ struct AlmostNoData<T>(Option<T>);
 struct EvenLessData<T>(Option<T>);
 
 impl<T> Bar for T where EvenLessData<T>: Baz {
-//~^ ERROR: overflow evaluating the requirement
-//~| ERROR: overflow evaluating the requirement
   fn answer(self) {
     let val: EvenLessData<T> = EvenLessData(None);
   }
 }
 
 impl<T> Baz for T where AlmostNoData<T>: Bar {
-//~^ ERROR: overflow evaluating the requirement
-//~| ERROR: overflow evaluating the requirement
   fn answer(self) {
     let val: NoData<T> = AlmostNoData(None);
   }