Auto merge of rust-lang#80417 - Mark-Simulacrum:beta-next, r=Mark-Sim…

…ulacrum

[beta] backports

This backports the following to 1.49:

*  Revert change to trait evaluation order rust-lang#80132
*  Don't allow `const` to begin a nonterminal rust-lang#80135
*  Prevent caching normalization results with a cycle rust-lang#80246

r? `@Mark-Simulacrum`

compiler/rustc_infer/src/traits/project.rs

@@ -90,6 +90,7 @@ impl ProjectionCacheKey<'tcx> {
 pub enum ProjectionCacheEntry<'tcx> {
     InProgress,
     Ambiguous,
+    Recur,
     Error,
     NormalizedTy(NormalizedTy<'tcx>),
 }
@@ -143,7 +144,12 @@ impl<'tcx> ProjectionCache<'_, 'tcx> {
             "ProjectionCacheEntry::insert_ty: adding cache entry: key={:?}, value={:?}",
             key, value
         );
-        let fresh_key = self.map().insert(key, ProjectionCacheEntry::NormalizedTy(value));
+        let mut map = self.map();
+        if let Some(ProjectionCacheEntry::Recur) = map.get(&key) {
+            debug!("Not overwriting Recur");
+            return;
+        }
+        let fresh_key = map.insert(key, ProjectionCacheEntry::NormalizedTy(value));
         assert!(!fresh_key, "never started projecting `{:?}`", key);
     }
 
@@ -197,6 +203,14 @@ impl<'tcx> ProjectionCache<'_, 'tcx> {
         assert!(!fresh, "never started projecting `{:?}`", key);
     }
 
+    /// Indicates that while trying to normalize `key`, `key` was required to
+    /// be normalized again. Selection or evaluation should eventually report
+    /// an error here.
+    pub fn recur(&mut self, key: ProjectionCacheKey<'tcx>) {
+        let fresh = self.map().insert(key, ProjectionCacheEntry::Recur);
+        assert!(!fresh, "never started projecting `{:?}`", key);
+    }
+
     /// Indicates that trying to normalize `key` resulted in
     /// error.
     pub fn error(&mut self, key: ProjectionCacheKey<'tcx>) {

compiler/rustc_parse/src/parser/nonterminal.rs

@@ -27,6 +27,8 @@ impl<'a> Parser<'a> {
                 token.can_begin_expr()
                 // This exception is here for backwards compatibility.
                 && !token.is_keyword(kw::Let)
+                // This exception is here for backwards compatibility.
+                && !token.is_keyword(kw::Const)
             }
             NonterminalKind::Ty => token.can_begin_type(),
             NonterminalKind::Ident => get_macro_ident(token).is_some(),

compiler/rustc_trait_selection/src/traits/project.rs

@@ -496,12 +496,6 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             return Ok(None);
         }
         Err(ProjectionCacheEntry::InProgress) => {
-            // If while normalized A::B, we are asked to normalize
-            // A::B, just return A::B itself. This is a conservative
-            // answer, in the sense that A::B *is* clearly equivalent
-            // to A::B, though there may be a better value we can
-            // find.
-
             // Under lazy normalization, this can arise when
             // bootstrapping.  That is, imagine an environment with a
             // where-clause like `A::B == u32`. Now, if we are asked
@@ -512,6 +506,14 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
 
             debug!("found cache entry: in-progress");
 
+            // Cache that normalizing this projection resulted in a cycle. This
+            // should ensure that, unless this happens within a snapshot that's
+            // rolled back, fulfillment or evaluation will notice the cycle.
+
+            infcx.inner.borrow_mut().projection_cache().recur(cache_key);
+            return Err(InProgress);
+        }
+        Err(ProjectionCacheEntry::Recur) => {
             return Err(InProgress);
         }
         Err(ProjectionCacheEntry::NormalizedTy(ty)) => {
@@ -734,7 +736,14 @@ fn project_type<'cx, 'tcx>(
 
     if !selcx.tcx().sess.recursion_limit().value_within_limit(obligation.recursion_depth) {
         debug!("project: overflow!");
-        return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
+        match selcx.query_mode() {
+            super::TraitQueryMode::Standard => {
+                selcx.infcx().report_overflow_error(&obligation, true);
+            }
+            super::TraitQueryMode::Canonical => {
+                return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
+            }
+        }
     }
 
     let obligation_trait_ref = &obligation.predicate.trait_ref(selcx.tcx());

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

@@ -335,7 +335,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn vtable_impl(
         &mut self,
         impl_def_id: DefId,
-        mut substs: Normalized<'tcx, SubstsRef<'tcx>>,
+        substs: Normalized<'tcx, SubstsRef<'tcx>>,
         cause: ObligationCause<'tcx>,
         recursion_depth: usize,
         param_env: ty::ParamEnv<'tcx>,
@@ -357,9 +357,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // relying on projections in the impl-trait-ref.
         //
         // e.g., `impl<U: Tr, V: Iterator<Item=U>> Foo<<U as Tr>::T> for V`
-        substs.obligations.append(&mut impl_obligations);
+        impl_obligations.extend(substs.obligations);
 
-        ImplSourceUserDefinedData { impl_def_id, substs: substs.value, nested: substs.obligations }
+        ImplSourceUserDefinedData { impl_def_id, substs: substs.value, nested: impl_obligations }
     }
 
     fn confirm_object_candidate(

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

@@ -290,6 +290,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         self.infcx.tcx
     }
 
+    pub(super) fn query_mode(&self) -> TraitQueryMode {
+        self.query_mode
+    }
+
     ///////////////////////////////////////////////////////////////////////////
     // Selection
     //

src/test/ui/associated-types/defaults-cyclic-fail-1.rs

@@ -24,13 +24,13 @@ impl Tr for u32 {
 // ...but not in an impl that redefines one of the types.
 impl Tr for bool {
     type A = Box<Self::B>;
-    //~^ ERROR type mismatch resolving `<bool as Tr>::B == _`
+    //~^ ERROR overflow evaluating the requirement `<bool as Tr>::B == _`
 }
 // (the error is shown twice for some reason)
 
 impl Tr for usize {
     type B = &'static Self::A;
-    //~^ ERROR type mismatch resolving `<usize as Tr>::A == _`
+    //~^ ERROR overflow evaluating the requirement `<usize as Tr>::A == _`
 }
 
 fn main() {

src/test/ui/associated-types/defaults-cyclic-fail-1.stderr

@@ -1,15 +1,15 @@
-error[E0271]: type mismatch resolving `<bool as Tr>::B == _`
+error[E0275]: overflow evaluating the requirement `<bool as Tr>::B == _`
   --> $DIR/defaults-cyclic-fail-1.rs:26:5
    |
 LL |     type A = Box<Self::B>;
-   |     ^^^^^^^^^^^^^^^^^^^^^^ cyclic type of infinite size
+   |     ^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0271]: type mismatch resolving `<usize as Tr>::A == _`
+error[E0275]: overflow evaluating the requirement `<usize as Tr>::A == _`
   --> $DIR/defaults-cyclic-fail-1.rs:32:5
    |
 LL |     type B = &'static Self::A;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ cyclic type of infinite size
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0275`.

src/test/ui/associated-types/defaults-cyclic-fail-2.rs

@@ -25,13 +25,13 @@ impl Tr for u32 {
 
 impl Tr for bool {
     type A = Box<Self::B>;
-    //~^ ERROR type mismatch resolving `<bool as Tr>::B == _`
+    //~^ ERROR overflow evaluating the requirement `<bool as Tr>::B == _`
 }
 // (the error is shown twice for some reason)
 
 impl Tr for usize {
     type B = &'static Self::A;
-    //~^ ERROR type mismatch resolving `<usize as Tr>::A == _`
+    //~^ ERROR overflow evaluating the requirement `<usize as Tr>::A == _`
 }
 
 fn main() {

src/test/ui/associated-types/defaults-cyclic-fail-2.stderr

@@ -1,15 +1,15 @@
-error[E0271]: type mismatch resolving `<bool as Tr>::B == _`
+error[E0275]: overflow evaluating the requirement `<bool as Tr>::B == _`
   --> $DIR/defaults-cyclic-fail-2.rs:27:5
    |
 LL |     type A = Box<Self::B>;
-   |     ^^^^^^^^^^^^^^^^^^^^^^ cyclic type of infinite size
+   |     ^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0271]: type mismatch resolving `<usize as Tr>::A == _`
+error[E0275]: overflow evaluating the requirement `<usize as Tr>::A == _`
   --> $DIR/defaults-cyclic-fail-2.rs:33:5
    |
 LL |     type B = &'static Self::A;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ cyclic type of infinite size
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0275`.

src/test/ui/associated-types/impl-wf-cycle-1.rs

@@ -0,0 +1,29 @@
+// Regression test for #79714
+
+trait Baz {}
+impl Baz for () {}
+impl<T> Baz for (T,) {}
+
+trait Fiz {}
+impl Fiz for bool {}
+
+trait Grault {
+    type A;
+    type B;
+}
+
+impl<T: Grault> Grault for (T,)
+where
+    Self::A: Baz,
+    Self::B: Fiz,
+{
+    type A = ();
+    //~^ ERROR overflow evaluating the requirement `<(T,) as Grault>::A == _`
+    type B = bool;
+    //~^ ERROR overflow evaluating the requirement `<(T,) as Grault>::A == _`
+}
+//~^^^^^^^^^^ ERROR overflow evaluating the requirement `<(T,) as Grault>::A == _`
+
+fn main() {
+    let x: <(_,) as Grault>::A = ();
+}

src/test/ui/associated-types/impl-wf-cycle-1.stderr

@@ -0,0 +1,36 @@
+error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
+  --> $DIR/impl-wf-cycle-1.rs:15:1
+   |
+LL | / impl<T: Grault> Grault for (T,)
+LL | | where
+LL | |     Self::A: Baz,
+LL | |     Self::B: Fiz,
+...  |
+LL | |
+LL | | }
+   | |_^
+   |
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+
+error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
+  --> $DIR/impl-wf-cycle-1.rs:20:5
+   |
+LL |     type A = ();
+   |     ^^^^^^^^^^^^
+   |
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+
+error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
+  --> $DIR/impl-wf-cycle-1.rs:22:5
+   |
+LL |     type B = bool;
+   |     ^^^^^^^^^^^^^^
+   |
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0275`.

src/test/ui/associated-types/impl-wf-cycle-2.rs

@@ -0,0 +1,16 @@
+// Regression test for #79714
+
+trait Grault {
+    type A;
+}
+
+impl<T: Grault> Grault for (T,)
+where
+    Self::A: Copy,
+{
+    type A = ();
+    //~^ ERROR overflow evaluating the requirement `<(T,) as Grault>::A == _`
+}
+//~^^^^^^^ ERROR overflow evaluating the requirement `<(T,) as Grault>::A == _`
+
+fn main() {}

src/test/ui/associated-types/impl-wf-cycle-2.stderr

@@ -0,0 +1,25 @@
+error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
+  --> $DIR/impl-wf-cycle-2.rs:7:1
+   |
+LL | / impl<T: Grault> Grault for (T,)
+LL | | where
+LL | |     Self::A: Copy,
+LL | | {
+LL | |     type A = ();
+LL | |
+LL | | }
+   | |_^
+   |
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+
+error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
+  --> $DIR/impl-wf-cycle-2.rs:11:5
+   |
+LL |     type A = ();
+   |     ^^^^^^^^^^^^
+   |
+   = note: required because of the requirements on the impl of `Grault` for `(T,)`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0275`.

src/test/ui/inline-const/macro-with-const.rs

@@ -0,0 +1,20 @@
+// check-pass
+
+macro_rules! exp {
+    (const $n:expr) => {
+        $n
+    };
+}
+
+macro_rules! stmt {
+    (exp $e:expr) => {
+        $e
+    };
+    (exp $($t:tt)+) => {
+        exp!($($t)+)
+    };
+}
+
+fn main() {
+    stmt!(exp const 1);
+}

src/test/ui/issues/issue-23122-2.stderr

@@ -1,11 +1,10 @@
-error[E0275]: overflow evaluating the requirement `<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<T as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next: Sized`
+error[E0275]: overflow evaluating the requirement `<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<T as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next`
   --> $DIR/issue-23122-2.rs:9:5
    |
 LL |     type Next = <GetNext<T::Next> as Next>::Next;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`issue_23122_2`)
-   = note: required because of the requirements on the impl of `Next` for `GetNext<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<T as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next as Next>::Next>`
 
 error: aborting due to previous error
 

src/test/ui/traits/impl-evaluation-order.rs

@@ -0,0 +1,39 @@
+// Regression test for #79902
+
+// Check that evaluation (which is used to determine whether to copy a type in
+// MIR building) evaluates bounds from normalizing an impl after evaluating
+// any bounds on the impl.
+
+// check-pass
+
+trait A {
+    type B;
+}
+trait M {}
+
+struct G<T, U>(*const T, *const U);
+
+impl<T, U> Clone for G<T, U> {
+    fn clone(&self) -> Self {
+        G { ..*self }
+    }
+}
+
+impl<T, U> Copy for G<T, U::B>
+where
+    T: A<B = U>,
+    U: A,
+{
+}
+
+impl A for () {
+    type B = ();
+}
+
+fn is_m<T: M>(_: T) {}
+
+fn main() {
+    let x = G(&(), &());
+    drop(x);
+    drop(x);
+}