Don't bind hidden types when searching for matching impls

compiler/rustc_const_eval/src/transform/validate.rs

@@ -169,8 +169,13 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             // Equal types, all is good.
             return true;
         }
+        // Normalization reveals opaque types, but we may be validating MIR while computing
+        // said opaque types, causing cycles.
+        if (src, dest).has_opaque_types() {
+            return true;
+        }
         // Normalize projections and things like that.
-        let param_env = self.param_env;
+        let param_env = self.param_env.with_reveal_all_normalized(self.tcx);
         let src = self.tcx.normalize_erasing_regions(param_env, src);
         let dest = self.tcx.normalize_erasing_regions(param_env, dest);
 

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -163,7 +163,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     Ok(_) => span_bug!(
                         cause.span,
                         "opaque types are never equal to anything but themselves: {:#?}",
-                        (a, b)
+                        (a.kind(), b.kind())
                     ),
                     Err(e) => Err(e),
                 }
@@ -450,10 +450,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         trace!(?origin);
         origin
     }
-
-    pub fn opaque_types(&self) -> OpaqueTypeMap<'tcx> {
-        self.inner.borrow().opaque_type_storage.opaque_types()
-    }
 }
 
 // Visitor that requires that (almost) all regions in the type visited outlive

compiler/rustc_infer/src/infer/opaque_types/table.rs

@@ -29,14 +29,6 @@ impl<'tcx> OpaqueTypeStorage<'tcx> {
         }
     }
 
-    pub fn get_decl(&self, key: &OpaqueTypeKey<'tcx>) -> Option<&OpaqueTypeDecl<'tcx>> {
-        self.opaque_types.get(key)
-    }
-
-    pub fn opaque_types(&self) -> OpaqueTypeMap<'tcx> {
-        self.opaque_types.clone()
-    }
-
     #[instrument(level = "debug")]
     pub fn take_opaque_types(&mut self) -> OpaqueTypeMap<'tcx> {
         std::mem::take(&mut self.opaque_types)
@@ -69,7 +61,7 @@ pub struct OpaqueTypeTable<'a, 'tcx> {
 
 impl<'a, 'tcx> OpaqueTypeTable<'a, 'tcx> {
     #[instrument(skip(self), level = "debug")]
-    pub fn register(
+    pub(crate) fn register(
         &mut self,
         key: OpaqueTypeKey<'tcx>,
         hidden_type: OpaqueHiddenType<'tcx>,

compiler/rustc_trait_selection/src/traits/codegen.rs

@@ -90,10 +90,11 @@ pub fn codegen_fulfill_obligation<'tcx>(
         });
         let impl_source = drain_fulfillment_cx_or_panic(&infcx, &mut fulfill_cx, impl_source);
 
-        // We may constrain the hidden types of opaque types in this query, but this is
-        // not information our callers need, as all that information is handled by borrowck
-        // and typeck.
-        drop(infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types());
+        // There should be no opaque types during codegen, they all get revealed.
+        let opaque_types = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
+        if !opaque_types.is_empty() {
+            bug!("{:#?}", opaque_types);
+        }
 
         debug!("Cache miss: {:?} => {:?}", trait_ref, impl_source);
         Ok(impl_source)

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

@@ -2163,6 +2163,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let InferOk { obligations, .. } = self
             .infcx
             .at(&cause, obligation.param_env)
+            .define_opaque_types(false)
             .eq(placeholder_obligation_trait_ref, impl_trait_ref)
             .map_err(|e| debug!("match_impl: failed eq_trait_refs due to `{}`", e))?;
         nested_obligations.extend(obligations);

src/test/ui/impl-trait/nested_impl_trait.rs

@@ -4,7 +4,7 @@ fn fine(x: impl Into<u32>) -> impl Into<u32> { x }
 
 fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
 //~^ ERROR nested `impl Trait` is not allowed
-//~| ERROR `impl Into<u32>` doesn't implement `Debug`
+//~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 
 fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
 //~^ ERROR nested `impl Trait` is not allowed
@@ -17,7 +17,7 @@ struct X;
 impl X {
     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
     //~^ ERROR nested `impl Trait` is not allowed
-    //~| ERROR `impl Into<u32>` doesn't implement `Debug`
+    //~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
 }
 
 fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {

src/test/ui/impl-trait/nested_impl_trait.stderr

@@ -46,27 +46,21 @@ error[E0562]: `impl Trait` not allowed outside of function and method return typ
 LL | fn allowed_in_ret_type() -> impl Fn() -> impl Into<u32> {
    |                                          ^^^^^^^^^^^^^^
 
-error[E0277]: `impl Into<u32>` doesn't implement `Debug`
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:5:70
    |
 LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
-   |                                                                      ^ `impl Into<u32>` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |                                                                      ^ the trait `From<impl Into<u32>>` is not implemented for `impl Debug`
    |
-help: consider further restricting this bound
-   |
-LL | fn bad_in_ret_position(x: impl Into<u32> + std::fmt::Debug) -> impl Into<impl Debug> { x }
-   |                                          +++++++++++++++++
+   = note: required because of the requirements on the impl of `Into<impl Debug>` for `impl Into<u32>`
 
-error[E0277]: `impl Into<u32>` doesn't implement `Debug`
+error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
   --> $DIR/nested_impl_trait.rs:18:58
    |
 LL |     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
-   |                                                          ^ `impl Into<u32>` cannot be formatted using `{:?}` because it doesn't implement `Debug`
-   |
-help: consider further restricting this bound
+   |                                                          ^ the trait `From<impl Into<u32>>` is not implemented for `impl Debug`
    |
-LL |     fn bad(x: impl Into<u32> + std::fmt::Debug) -> impl Into<impl Debug> { x }
-   |                              +++++++++++++++++
+   = note: required because of the requirements on the impl of `Into<impl Debug>` for `impl Into<u32>`
 
 error: aborting due to 8 previous errors
 

src/test/ui/impl-trait/projection.rs

@@ -0,0 +1,29 @@
+// build-pass
+// needs to be build-pass, because it is a regression test for a mir validation failure
+// that only happens during codegen.
+
+struct D;
+
+trait Tr {
+    type It;
+    fn foo(self) -> Option<Self::It>;
+}
+
+impl<'a> Tr for &'a D {
+    type It = ();
+    fn foo(self) -> Option<()> { None }
+}
+
+fn run<F>(f: F)
+    where for<'a> &'a D: Tr,
+          F: Fn(<&D as Tr>::It),
+{
+    let d = &D;
+    while let Some(i) = d.foo() {
+        f(i);
+    }
+}
+
+fn main() {
+    run(|_| {});
+}

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs

@@ -0,0 +1,17 @@
+#![feature(type_alias_impl_trait)]
+
+type Foo = impl PartialEq<(Foo, i32)>;
+
+struct Bar;
+
+impl PartialEq<(Foo, i32)> for Bar {
+    fn eq(&self, _other: &(Foo, i32)) -> bool {
+        true
+    }
+}
+
+fn foo() -> Foo {
+    Bar //~ ERROR can't compare `Bar` with `(Bar, i32)`
+}
+
+fn main() {}

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.stderr

@@ -0,0 +1,11 @@
+error[E0277]: can't compare `Bar` with `(Bar, i32)`
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs:14:5
+   |
+LL |     Bar
+   |     ^^^ no implementation for `Bar == (Bar, i32)`
+   |
+   = help: the trait `PartialEq<(Bar, i32)>` is not implemented for `Bar`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration.rs

@@ -2,36 +2,18 @@
 
 #![feature(type_alias_impl_trait)]
 
-mod direct {
-    type Foo = impl PartialEq<(Foo, i32)>;
+type Foo = impl PartialEq<(Foo, i32)>;
 
-    struct Bar;
+struct Bar;
 
-    impl PartialEq<(Foo, i32)> for Bar {
-        fn eq(&self, _other: &(Foo, i32)) -> bool {
-            true
-        }
-    }
-
-    fn foo() -> Foo {
-        Bar
+impl PartialEq<(Bar, i32)> for Bar {
+    fn eq(&self, _other: &(Bar, i32)) -> bool {
+        true
     }
 }
 
-mod indirect {
-    type Foo = impl PartialEq<(Foo, i32)>;
-
-    struct Bar;
-
-    impl PartialEq<(Bar, i32)> for Bar {
-        fn eq(&self, _other: &(Bar, i32)) -> bool {
-            true
-        }
-    }
-
-    fn foo() -> Foo {
-        Bar
-    }
+fn foo() -> Foo {
+    Bar
 }
 
 fn main() {}

src/test/ui/impl-trait/trait_resolution.rs

@@ -0,0 +1,30 @@
+// check-pass
+
+use std::fmt::Debug;
+
+pub struct EventStream<S> {
+    stream: S,
+}
+
+impl<S: Debug> EventStream<S> {
+    fn into_stream(self) -> impl Debug {
+        unimplemented!()
+    }
+
+    pub fn into_reader(self) -> impl Debug {
+        ReaderStream::from(self.into_stream())
+    }
+}
+
+#[derive(Debug)]
+pub struct ReaderStream<S> {
+    stream: S,
+}
+
+impl<S> From<S> for ReaderStream<S> {
+    fn from(stream: S) -> Self {
+        ReaderStream { stream }
+    }
+}
+
+fn main() {}