Implementation of GATs outlives lint

compiler/rustc_infer/src/infer/mod.rs

@@ -1255,16 +1255,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         self.tainted_by_errors_flag.set(true)
     }
 
-    /// Process the region constraints and report any errors that
+    /// Process the region constraints and return any any errors that
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
-    pub fn resolve_regions_and_report_errors(
+    pub fn resolve_regions(
         &self,
         region_context: DefId,
         outlives_env: &OutlivesEnvironment<'tcx>,
         mode: RegionckMode,
-    ) {
+    ) -> Vec<RegionResolutionError<'tcx>> {
         let (var_infos, data) = {
             let mut inner = self.inner.borrow_mut();
             let inner = &mut *inner;
@@ -1290,6 +1290,21 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
         assert!(old_value.is_none());
 
+        errors
+    }
+
+    /// Process the region constraints and report any errors that
+    /// result. After this, no more unification operations should be
+    /// done -- or the compiler will panic -- but it is legal to use
+    /// `resolve_vars_if_possible` as well as `fully_resolve`.
+    pub fn resolve_regions_and_report_errors(
+        &self,
+        region_context: DefId,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+        mode: RegionckMode,
+    ) {
+        let errors = self.resolve_regions(region_context, outlives_env, mode);
+
         if !self.is_tainted_by_errors() {
             // As a heuristic, just skip reporting region errors
             // altogether if other errors have been reported while

compiler/rustc_typeck/src/check/regionck.rs

@@ -104,7 +104,7 @@ macro_rules! ignore_err {
     };
 }
 
-trait OutlivesEnvironmentExt<'tcx> {
+pub(crate) trait OutlivesEnvironmentExt<'tcx> {
     fn add_implied_bounds(
         &mut self,
         infcx: &InferCtxt<'a, 'tcx>,

compiler/rustc_typeck/src/lib.rs

@@ -69,6 +69,7 @@ This API is completely unstable and subject to change.
 #![feature(never_type)]
 #![feature(slice_partition_dedup)]
 #![feature(control_flow_enum)]
+#![feature(hash_drain_filter)]
 #![recursion_limit = "256"]
 
 #[macro_use]

src/test/ui/generic-associated-types/collections-project-default.rs

@@ -8,7 +8,7 @@
 // check that we don't normalize with trait defaults.
 
 trait Collection<T> {
-    type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter;
+    type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter, Self: 'iter;
     type Family: CollectionFamily;
     // Test associated type defaults with parameters
     type Sibling<U>: Collection<U> =

src/test/ui/generic-associated-types/collections.rs

@@ -8,7 +8,7 @@
 // run-pass
 
 trait Collection<T> {
-    type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter;
+    type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter, Self: 'iter;
     type Family: CollectionFamily;
     // Test associated type defaults with parameters
     type Sibling<U>: Collection<U> =

src/test/ui/generic-associated-types/generic-associated-type-bounds.rs

@@ -3,7 +3,7 @@
 #![feature(generic_associated_types)]
 
 pub trait X {
-    type Y<'a>;
+    type Y<'a> where Self: 'a;
     fn m(&self) -> Self::Y<'_>;
 }
 

src/test/ui/generic-associated-types/issue-70303.rs

@@ -3,7 +3,7 @@
 #![feature(generic_associated_types)]
 
 trait Document {
-    type Cursor<'a>: DocCursor<'a>;
+    type Cursor<'a>: DocCursor<'a> where Self: 'a;
 
     fn cursor(&self) -> Self::Cursor<'_>;
 }

src/test/ui/generic-associated-types/issue-76535.rs

@@ -3,7 +3,7 @@
 pub trait SubTrait {}
 
 pub trait SuperTrait {
-    type SubType<'a>: SubTrait;
+    type SubType<'a>: SubTrait where Self: 'a;
 
     fn get_sub<'a>(&'a mut self) -> Self::SubType<'a>;
 }

src/test/ui/generic-associated-types/issue-76535.stderr

@@ -7,7 +7,7 @@ LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruc
 note: associated type defined here, with 1 lifetime parameter: `'a`
   --> $DIR/issue-76535.rs:6:10
    |
-LL |     type SubType<'a>: SubTrait;
+LL |     type SubType<'a>: SubTrait where Self: 'a;
    |          ^^^^^^^ --
 help: add missing lifetime argument
    |
@@ -25,7 +25,7 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
    |
 LL | pub trait SuperTrait {
    |           ---------- this trait cannot be made into an object...
-LL |     type SubType<'a>: SubTrait;
+LL |     type SubType<'a>: SubTrait where Self: 'a;
    |          ^^^^^^^ ...because it contains the generic associated type `SubType`
    = help: consider moving `SubType` to another trait
 
@@ -40,7 +40,7 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
    |
 LL | pub trait SuperTrait {
    |           ---------- this trait cannot be made into an object...
-LL |     type SubType<'a>: SubTrait;
+LL |     type SubType<'a>: SubTrait where Self: 'a;
    |          ^^^^^^^ ...because it contains the generic associated type `SubType`
    = help: consider moving `SubType` to another trait
    = note: required because of the requirements on the impl of `CoerceUnsized<Box<dyn SuperTrait<SubType = SubStruct<'_>>>>` for `Box<SuperStruct>`

src/test/ui/generic-associated-types/issue-79422.rs

@@ -17,12 +17,12 @@ impl<'a, T> RefCont<'a, T> for Box<T> {
 }
 
 trait MapLike<K, V> {
-    type VRefCont<'a>: RefCont<'a, V>;
+    type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
     fn get<'a>(&'a self, key: &K) -> Option<Self::VRefCont<'a>>;
 }
 
 impl<K: Ord, V: 'static> MapLike<K, V> for std::collections::BTreeMap<K, V> {
-    type VRefCont<'a> = &'a V;
+    type VRefCont<'a> where Self: 'a = &'a V;
     fn get<'a>(&'a self, key: &K) -> Option<&'a V> {
         std::collections::BTreeMap::get(self, key)
     }

src/test/ui/generic-associated-types/issue-79422.stderr

@@ -7,7 +7,7 @@ LL |         as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
 note: associated type defined here, with 1 lifetime parameter: `'a`
   --> $DIR/issue-79422.rs:20:10
    |
-LL |     type VRefCont<'a>: RefCont<'a, V>;
+LL |     type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
    |          ^^^^^^^^ --
 help: add missing lifetime argument
    |
@@ -25,7 +25,7 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
    |
 LL | trait MapLike<K, V> {
    |       ------- this trait cannot be made into an object...
-LL |     type VRefCont<'a>: RefCont<'a, V>;
+LL |     type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
    |          ^^^^^^^^ ...because it contains the generic associated type `VRefCont`
    = help: consider moving `VRefCont` to another trait
 
@@ -40,7 +40,7 @@ note: for a trait to be "object safe" it needs to allow building a vtable to all
    |
 LL | trait MapLike<K, V> {
    |       ------- this trait cannot be made into an object...
-LL |     type VRefCont<'a>: RefCont<'a, V>;
+LL |     type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
    |          ^^^^^^^^ ...because it contains the generic associated type `VRefCont`
    = help: consider moving `VRefCont` to another trait
    = note: required because of the requirements on the impl of `CoerceUnsized<Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>>` for `Box<BTreeMap<u8, u8>>`

src/test/ui/generic-associated-types/issue-86787.rs

@@ -9,6 +9,7 @@ enum Either<L, R> {
 pub trait HasChildrenOf {
     type T;
     type TRef<'a>;
+    //~^ Missing required bounds
 
     fn ref_children<'a>(&'a self) -> Vec<Self::TRef<'a>>;
     fn take_children(self) -> Vec<Self::T>;
@@ -20,9 +21,9 @@ where
     Right: HasChildrenOf,
 {
     type T = Either<Left::T, Right::T>;
+    // We used to error below because the where clause doesn't match the trait.
+    // Now, we error early on the trait itself.
     type TRef<'a>
-    //~^ `impl` associated type signature
-    //~^^ `impl` associated type signature
     where
     <Left as HasChildrenOf>::T: 'a,
     <Right as HasChildrenOf>::T: 'a

src/test/ui/generic-associated-types/issue-86787.stderr

@@ -1,32 +1,10 @@
-error: `impl` associated type signature for `TRef` doesn't match `trait` associated type signature
-  --> $DIR/issue-86787.rs:23:5
+error: Missing required bounds on TRef
+  --> $DIR/issue-86787.rs:11:5
    |
-LL |       type TRef<'a>;
-   |       -------------- expected
-...
-LL | /     type TRef<'a>
-LL | |
-LL | |
-LL | |     where
-LL | |     <Left as HasChildrenOf>::T: 'a,
-LL | |     <Right as HasChildrenOf>::T: 'a
-LL | |     = Either<&'a Left::T, &'a Right::T>;
-   | |________________________________________^ found
+LL |     type TRef<'a>;
+   |     ^^^^^^^^^^^^^-
+   |                  |
+   |                  help: add the required where clauses: `where Self: 'a`
 
-error: `impl` associated type signature for `TRef` doesn't match `trait` associated type signature
-  --> $DIR/issue-86787.rs:23:5
-   |
-LL |       type TRef<'a>;
-   |       -------------- expected
-...
-LL | /     type TRef<'a>
-LL | |
-LL | |
-LL | |     where
-LL | |     <Left as HasChildrenOf>::T: 'a,
-LL | |     <Right as HasChildrenOf>::T: 'a
-LL | |     = Either<&'a Left::T, &'a Right::T>;
-   | |________________________________________^ found
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 

src/test/ui/generic-associated-types/issue-88287.rs

@@ -13,7 +13,8 @@ trait SearchableResource<Criteria> {
 trait SearchableResourceExt<Criteria>: SearchableResource<Criteria> {
     type Future<'f, A: 'f + ?Sized, B: 'f>: Future<Output = Result<Vec<A::SearchResult>, ()>> + 'f
     where
-        A: SearchableResource<B>;
+        A: SearchableResource<B>,
+        Self: 'f;
 
     fn search<'c>(&'c self, client: &'c ()) -> Self::Future<'c, Self, Criteria>;
 }
@@ -29,6 +30,7 @@ where
     type Future<'f, A, B: 'f>
     where
         A: SearchableResource<B> + ?Sized + 'f,
+        Self: 'f,
     = SearchFutureTy<'f, A, B>;
 
     fn search<'c>(&'c self, _client: &'c ()) -> Self::Future<'c, Self, Criteria> {

src/test/ui/generic-associated-types/issue-88360.rs

@@ -1,13 +1,14 @@
 #![feature(generic_associated_types)]
 
 trait GatTrait {
-    type Gat<'a>;
+    type Gat<'a> where Self: 'a;
 
     fn test(&self) -> Self::Gat<'_>;
 }
 
 trait SuperTrait<T>
 where
+    Self: 'static,
     for<'a> Self: GatTrait<Gat<'a> = &'a T>,
 {
     fn copy(&self) -> Self::Gat<'_> where T: Copy {

src/test/ui/generic-associated-types/issue-88360.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/issue-88360.rs:14:9
+  --> $DIR/issue-88360.rs:15:9
    |
 LL | trait SuperTrait<T>
    |                  - this type parameter

src/test/ui/generic-associated-types/projection-type-lifetime-mismatch.rs

@@ -1,7 +1,7 @@
 #![feature(generic_associated_types)]
 
 pub trait X {
-    type Y<'a>;
+    type Y<'a> where Self: 'a;
     fn m(&self) -> Self::Y<'_>;
 }
 

src/test/ui/generic-associated-types/self-outlives-lint.rs

@@ -0,0 +1,173 @@
+#![feature(generic_associated_types)]
+
+// check-fail
+
+use std::fmt::Debug;
+
+// We have a `&'a self`, so we need a `Self: 'a`
+trait Iterable {
+    type Item<'x>;
+    //~^ Missing required bounds
+    fn iter<'a>(&'a self) -> Self::Item<'a>;
+}
+
+/*
+impl<T> Iterable for T {
+    type Item<'a> = &'a T;
+    fn iter<'a>(&'a self) -> Self::Item<'a> {
+        self
+    }
+}
+*/
+
+// We have a `&'a T`, so we need a `T: 'x`
+trait Deserializer<T> {
+    type Out<'x>;
+    //~^ Missing required bounds
+    fn deserialize<'a>(&self, input: &'a T) -> Self::Out<'a>;
+}
+
+/*
+impl<T> Deserializer<T> for () {
+    type Out<'a> = &'a T;
+    fn deserialize<'a>(&self, input: &'a T) -> Self::Out<'a> { input }
+}
+*/
+
+// We have a `&'b T` and a `'b: 'a`, so it is implied that `T: 'a`. Therefore, we need a `T: 'x`
+trait Deserializer2<T> {
+    type Out<'x>;
+    //~^ Missing required bounds
+    fn deserialize2<'a, 'b: 'a>(&self, input1: &'b T) -> Self::Out<'a>;
+}
+
+// We have a `&'a T` and a `&'b U`, so we need a `T: 'x` and a `U: 'y`
+trait Deserializer3<T, U> {
+    type Out<'x, 'y>;
+    //~^ Missing required bounds
+    fn deserialize2<'a, 'b>(&self, input: &'a T, input2: &'b U) -> Self::Out<'a, 'b>;
+}
+
+// `T` is a param on the function, so it can't be named by the associated type
+trait Deserializer4 {
+    type Out<'x>;
+    fn deserialize<'a, T>(&self, input: &'a T) -> Self::Out<'a>;
+}
+
+struct Wrap<T>(T);
+
+// We pass `Wrap<T>` and we see `&'z Wrap<T>`, so we require `D: 'x`
+trait Des {
+    type Out<'x, D>;
+    //~^ Missing required bounds
+    fn des<'z, T>(&self, data: &'z Wrap<T>) -> Self::Out<'z, Wrap<T>>;
+}
+/*
+impl Des for () {
+    type Out<'x, D> = &'x D; // Not okay
+    fn des<'a, T>(&self, data: &'a Wrap<T>) -> Self::Out<'a, Wrap<T>> {
+        data
+    }
+}
+*/
+
+// We have `T` and `'z` as GAT substs. Because of `&'z Wrap<T>`, there is an
+// implied bound that `T: 'z`, so we require `D: 'x`
+trait Des2 {
+    type Out<'x, D>;
+    //~^ Missing required bounds
+    fn des<'z, T>(&self, data: &'z Wrap<T>) -> Self::Out<'z, T>;
+}
+/*
+impl Des2 for () {
+    type Out<'x, D> = &'x D;
+    fn des<'a, T>(&self, data: &'a Wrap<T>) -> Self::Out<'a, T> {
+        &data.0
+    }
+}
+*/
+
+// We see `&'z T`, so we require `D: 'x`
+trait Des3 {
+    type Out<'x, D>;
+    //~^ Missing required bounds
+    fn des<'z, T>(&self, data: &'z T) -> Self::Out<'z, T>;
+}
+/*
+impl Des3 for () {
+    type Out<'x, D> = &'x D;
+    fn des<'a, T>(&self, data: &'a T) -> Self::Out<'a, T> {
+          data
+    }
+}
+*/
+
+// Similar case to before, except with GAT.
+trait NoGat<'a> {
+    type Bar;
+    fn method(&'a self) -> Self::Bar;
+}
+
+// Lifetime is not on function; except `Self: 'a`
+// FIXME: we require two bounds (`where Self: 'a, Self: 'b`) when we should only require one
+trait TraitLifetime<'a> {
+    type Bar<'b>;
+    //~^ Missing required bounds
+    fn method(&'a self) -> Self::Bar<'a>;
+}
+
+// Like above, but we have a where clause that can prove what we want
+// FIXME: we require two bounds (`where Self: 'a, Self: 'b`) when we should only require one
+trait TraitLifetimeWhere<'a> where Self: 'a {
+    type Bar<'b>;
+    //~^ Missing required bounds
+    fn method(&'a self) -> Self::Bar<'a>;
+}
+
+// Explicit bound instead of implicit; we want to still error
+trait ExplicitBound {
+    type Bar<'b>;
+    //~^ Missing required bounds
+    fn method<'b>(&self, token: &'b ()) -> Self::Bar<'b> where Self: 'b;
+}
+
+// The use of the GAT here is not in the return, we don't want to error
+trait NotInReturn {
+    type Bar<'b>;
+    fn method<'b>(&'b self) where Self::Bar<'b>: Debug;
+}
+
+// We obviously error for `Iterator`, but we should also error for `Item`
+trait IterableTwo {
+    type Item<'a>;
+    type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
+    //~^ Missing required bounds
+    fn iter<'a>(&'a self) -> Self::Iterator<'a>;
+}
+
+// We also should report region outlives clauses
+trait RegionOutlives {
+    type Bar<'a, 'b>;
+    //~^ Missing required bounds
+    fn foo<'x, 'y>(&self, input: &'x &'y ()) -> Self::Bar<'x, 'y>;
+}
+
+/*
+impl Foo for () {
+    type Bar<'a, 'b> = &'a &'b ();
+    fn foo<'x, 'y>(&self, input: &'x &'y ()) -> Self::Bar<'x, 'y> {
+        input
+    }
+}
+*/
+
+// If there are multiple methods that return the GAT, require a set of clauses
+// that can be satisfied by *all* methods
+trait MultipleMethods {
+    type Bar<'me>;
+
+    fn gimme<'a>(&'a self) -> Self::Bar<'a>;
+    fn gimme_default(&self) -> Self::Bar<'static>;
+}
+
+fn main() {}

src/test/ui/generic-associated-types/self-outlives-lint.stderr

@@ -0,0 +1,98 @@
+error: Missing required bounds on Item
+  --> $DIR/self-outlives-lint.rs:9:5
+   |
+LL |     type Item<'x>;
+   |     ^^^^^^^^^^^^^-
+   |                  |
+   |                  help: add the required where clauses: `where Self: 'x`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:25:5
+   |
+LL |     type Out<'x>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clauses: `where T: 'x`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:39:5
+   |
+LL |     type Out<'x>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clauses: `where T: 'x`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:46:5
+   |
+LL |     type Out<'x, 'y>;
+   |     ^^^^^^^^^^^^^^^^-
+   |                     |
+   |                     help: add the required where clauses: `where T: 'x, U: 'y`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:61:5
+   |
+LL |     type Out<'x, D>;
+   |     ^^^^^^^^^^^^^^^-
+   |                    |
+   |                    help: add the required where clauses: `where D: 'x`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:77:5
+   |
+LL |     type Out<'x, D>;
+   |     ^^^^^^^^^^^^^^^-
+   |                    |
+   |                    help: add the required where clauses: `where D: 'x`
+
+error: Missing required bounds on Out
+  --> $DIR/self-outlives-lint.rs:92:5
+   |
+LL |     type Out<'x, D>;
+   |     ^^^^^^^^^^^^^^^-
+   |                    |
+   |                    help: add the required where clauses: `where D: 'x`
+
+error: Missing required bounds on Bar
+  --> $DIR/self-outlives-lint.rs:114:5
+   |
+LL |     type Bar<'b>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clauses: `where Self: 'a, Self: 'b`
+
+error: Missing required bounds on Bar
+  --> $DIR/self-outlives-lint.rs:122:5
+   |
+LL |     type Bar<'b>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clauses: `where Self: 'a, Self: 'b`
+
+error: Missing required bounds on Bar
+  --> $DIR/self-outlives-lint.rs:129:5
+   |
+LL |     type Bar<'b>;
+   |     ^^^^^^^^^^^^-
+   |                 |
+   |                 help: add the required where clauses: `where Self: 'b`
+
+error: Missing required bounds on Iterator
+  --> $DIR/self-outlives-lint.rs:143:5
+   |
+LL |     type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |                                                       |
+   |                                                       help: add the required where clauses: `where Self: 'a`
+
+error: Missing required bounds on Bar
+  --> $DIR/self-outlives-lint.rs:150:5
+   |
+LL |     type Bar<'a, 'b>;
+   |     ^^^^^^^^^^^^^^^^-
+   |                     |
+   |                     help: add the required where clauses: `where 'a: 'b`
+
+error: aborting due to 12 previous errors
+

src/test/ui/generic-associated-types/streaming_iterator.rs

@@ -5,12 +5,12 @@
 use std::fmt::Display;
 
 trait StreamingIterator {
-    type Item<'a>;
+    type Item<'a> where Self: 'a;
     // Applying the lifetime parameter `'a` to `Self::Item` inside the trait.
     fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>;
 }
 
-struct Foo<T: StreamingIterator> {
+struct Foo<T: StreamingIterator + 'static> {
     // Applying a concrete lifetime to the constructor outside the trait.
     bar: <T as StreamingIterator>::Item<'static>,
 }
@@ -30,7 +30,7 @@ struct StreamEnumerate<I> {
 }
 
 impl<I: StreamingIterator> StreamingIterator for StreamEnumerate<I> {
-    type Item<'a> = (usize, I::Item<'a>);
+    type Item<'a> where Self: 'a = (usize, I::Item<'a>);
     fn next<'a>(&'a mut self) -> Option<Self::Item<'a>> {
         match self.iter.next() {
             None => None,
@@ -44,7 +44,7 @@ impl<I: StreamingIterator> StreamingIterator for StreamEnumerate<I> {
 }
 
 impl<I: Iterator> StreamingIterator for I {
-    type Item<'a> = <I as Iterator>::Item;
+    type Item<'a> where Self: 'a = <I as Iterator>::Item;
     fn next(&mut self) -> Option<<I as StreamingIterator>::Item<'_>> {
         Iterator::next(self)
     }

src/test/ui/generic-associated-types/variance_constraints.rs

@@ -3,7 +3,7 @@
 #![feature(generic_associated_types)]
 
 trait A {
-    type B<'a>;
+    type B<'a> where Self: 'a;
 
     fn make_b<'a>(&'a self) -> Self::B<'a>;
 }