Auto merge of rust-lang#97039 - cjgillot:no-rpit-hrtb, r=jackh726

bors · bors · commit b36be12d979d · 2022-05-14T15:47:22.000Z
Forbid nested opaque types to reference HRTB from opaque types. Avoids rust-lang#96194 Alternative to rust-lang#96970 r? `@oli-obk`
diff --git a/compiler/rustc_resolve/src/late/lifetimes.rs b/compiler/rustc_resolve/src/late/lifetimes.rs
@@ -1025,6 +1025,20 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                         }
                         self.uninsert_lifetime_on_error(lifetime, def.unwrap());
                     }
+                    if let hir::Node::Item(hir::Item {
+                        kind: hir::ItemKind::OpaqueTy { .. }, ..
+                    }) = self.tcx.hir().get(parent_id)
+                    {
+                        if !self.trait_definition_only {
+                            let mut err = self.tcx.sess.struct_span_err(
+                                lifetime.span,
+                                "higher kinded lifetime bounds on nested opaque types are not supported yet",
+                            );
+                            err.span_note(self.tcx.def_span(def_id), "lifetime declared here");
+                            err.emit();
+                        }
+                        self.uninsert_lifetime_on_error(lifetime, def.unwrap());
+                    }
                 }
 
                 // We want to start our early-bound indices at the end of the parent scope,
diff --git a/src/test/ui/impl-trait/issues/issue-54895.rs b/src/test/ui/impl-trait/issues/issue-54895.rs
@@ -1,5 +1,3 @@
-// check-pass
-
 trait Trait<'a> {
     type Out;
     fn call(&'a self) -> Self::Out;
@@ -15,6 +13,7 @@ impl<'a> Trait<'a> for X {
 }
 
 fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
+    //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
     X(())
 }
 
diff --git a/src/test/ui/impl-trait/issues/issue-54895.stderr b/src/test/ui/impl-trait/issues/issue-54895.stderr
@@ -0,0 +1,14 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-54895.rs:15:53
+   |
+LL | fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
+   |                                                     ^^
+   |
+note: lifetime declared here
+  --> $DIR/issue-54895.rs:15:20
+   |
+LL | fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {
+   |                    ^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/impl-trait/issues/issue-67830.nll.stderr b/src/test/ui/impl-trait/issues/issue-67830.nll.stderr
diff --git a/src/test/ui/impl-trait/issues/issue-67830.rs b/src/test/ui/impl-trait/issues/issue-67830.rs
@@ -19,7 +19,7 @@ where
 
 struct A;
 fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
-    //~^ ERROR implementation of `FnOnce` is not general enough
+    //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
     Wrap(|a| Some(a).into_iter())
 }
 
diff --git a/src/test/ui/impl-trait/issues/issue-67830.stderr b/src/test/ui/impl-trait/issues/issue-67830.stderr
@@ -1,11 +1,14 @@
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-67830.rs:21:14
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-67830.rs:21:62
    |
 LL | fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
+   |                                                              ^^
    |
-   = note: closure with signature `fn(&'2 A) -> std::option::IntoIter<&A>` must implement `FnOnce<(&'1 A,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 A,)>`, for some specific lifetime `'2`
+note: lifetime declared here
+  --> $DIR/issue-67830.rs:21:23
+   |
+LL | fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {
+   |                       ^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr b/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr
diff --git a/src/test/ui/impl-trait/issues/issue-88236-2.rs b/src/test/ui/impl-trait/issues/issue-88236-2.rs
@@ -13,11 +13,16 @@ impl<'a> Hrtb<'a> for &'a () {
 }
 
 fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+
 fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
-    &() //~^ ERROR implementation of `Hrtb` is not general enough
+    //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+    &()
 }
+
 fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
-    x //~^ ERROR implementation of `Hrtb` is not general enough
+    //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+    x
 }
 
 fn main() {}
diff --git a/src/test/ui/impl-trait/issues/issue-88236-2.stderr b/src/test/ui/impl-trait/issues/issue-88236-2.stderr
@@ -1,20 +1,38 @@
-error: implementation of `Hrtb` is not general enough
-  --> $DIR/issue-88236-2.rs:16:38
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:15:61
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                                                             ^^
+   |
+note: lifetime declared here
+  --> $DIR/issue-88236-2.rs:15:28
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                            ^^
+
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:18:80
    |
 LL | fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Hrtb` is not general enough
+   |                                                                                ^^
    |
-   = note: `Hrtb<'0>` would have to be implemented for the type `&()`, for any lifetime `'0`...
-   = note: ...but `Hrtb<'1>` is actually implemented for the type `&'1 ()`, for some specific lifetime `'1`
+note: lifetime declared here
+  --> $DIR/issue-88236-2.rs:18:47
+   |
+LL | fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
+   |                                               ^^
 
-error: implementation of `Hrtb` is not general enough
-  --> $DIR/issue-88236-2.rs:19:36
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236-2.rs:23:78
    |
 LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
-   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Hrtb` is not general enough
+   |                                                                              ^^
    |
-   = note: `Hrtb<'1>` would have to be implemented for the type `&()`, for any lifetime `'1`...
-   = note: ...but `Hrtb<'_>` is actually implemented for the type `&()`
+note: lifetime declared here
+  --> $DIR/issue-88236-2.rs:23:45
+   |
+LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {
+   |                                             ^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/impl-trait/issues/issue-88236.rs b/src/test/ui/impl-trait/issues/issue-88236.rs
@@ -1,5 +1,3 @@
-// check-pass
-
 // this used to cause stack overflows
 
 trait Hrtb<'a> {
@@ -15,5 +13,6 @@ impl<'a> Hrtb<'a> for &'a () {
 }
 
 fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
 
 fn main() {}
diff --git a/src/test/ui/impl-trait/issues/issue-88236.stderr b/src/test/ui/impl-trait/issues/issue-88236.stderr
@@ -0,0 +1,14 @@
+error: higher kinded lifetime bounds on nested opaque types are not supported yet
+  --> $DIR/issue-88236.rs:15:61
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                                                             ^^
+   |
+note: lifetime declared here
+  --> $DIR/issue-88236.rs:15:28
+   |
+LL | fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}
+   |                            ^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/impl-trait/nested-rpit-hrtb.rs b/src/test/ui/impl-trait/nested-rpit-hrtb.rs
@@ -0,0 +1,64 @@
+// Test the interaction between rested RPIT and HRTB.
+
+trait Foo<'a> {
+    type Assoc;
+}
+
+impl Foo<'_> for () {
+    type Assoc = ();
+}
+
+// Alternative version of `Foo` whose impl uses `'a`.
+trait Bar<'a> {
+    type Assoc;
+}
+
+impl<'a> Bar<'a> for () {
+    type Assoc = &'a ();
+}
+
+trait Qux<'a> {}
+
+impl Qux<'_> for () {}
+
+// This is not supported.
+fn one_hrtb_outlives() -> impl for<'a> Foo<'a, Assoc = impl Sized + 'a> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+
+// This is not supported.
+fn one_hrtb_trait_param() -> impl for<'a> Foo<'a, Assoc = impl Qux<'a>> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+
+fn one_hrtb_outlives_uses() -> impl for<'a> Bar<'a, Assoc = impl Sized + 'a> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+
+fn one_hrtb_trait_param_uses() -> impl for<'a> Bar<'a, Assoc = impl Qux<'a>> {}
+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet
+
+// This should pass.
+fn one_hrtb_mention_fn_trait_param<'b>() -> impl for<'a> Foo<'a, Assoc = impl Qux<'b>> {}
+
+// This should pass.
+fn one_hrtb_mention_fn_outlives<'b>() -> impl for<'a> Foo<'a, Assoc = impl Sized + 'b> {}
+
+// This should pass.
+fn one_hrtb_mention_fn_trait_param_uses<'b>() -> impl for<'a> Bar<'a, Assoc = impl Qux<'b>> {}
+
+// This should pass.
+fn one_hrtb_mention_fn_outlives_uses<'b>() -> impl for<'a> Bar<'a, Assoc = impl Sized + 'b> {}
+
+// This should pass.
+fn two_htrb_trait_param() -> impl for<'a> Foo<'a, Assoc = impl for<'b> Qux<'b>> {}
+
+// `'b` is not in scope for the outlives bound.
+fn two_htrb_outlives() -> impl for<'a> Foo<'a, Assoc = impl for<'b> Sized + 'b> {}
+//~^ ERROR use of undeclared lifetime name `'b` [E0261]
+
+// This should pass.
+fn two_htrb_trait_param_uses() -> impl for<'a> Bar<'a, Assoc = impl for<'b> Qux<'b>> {}
+
+// `'b` is not in scope for the outlives bound.
+fn two_htrb_outlives_uses() -> impl for<'a> Bar<'a, Assoc = impl for<'b> Sized + 'b> {}
+//~^ ERROR use of undeclared lifetime name `'b` [E0261]
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/nested-rpit-hrtb.stderr b/src/test/ui/impl-trait/nested-rpit-hrtb.stderr

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,3 @@`
`1`		`-// check-pass`
`2`		`-`
`3`	`1`	`trait Trait<'a> {`
`4`	`2`	`type Out;`
`5`	`3`	`fn call(&'a self) -> Self::Out;`
`@@ -15,6 +13,7 @@ impl<'a> Trait<'a> for X {`
`15`	`13`	`}`
`16`	`14`
`17`	`15`	`fn f() -> impl for<'a> Trait<'a, Out = impl Sized + 'a> {`
	`16`	`+ //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
`18`	`17`	`X(())`
`19`	`18`	`}`
`20`	`19`
Original file line number	Diff line number	Diff line change
`@@ -19,7 +19,7 @@ where`
`19`	`19`
`20`	`20`	`struct A;`
`21`	`21`	`fn test() -> impl for<'a> MyFn<&'a A, Output=impl Iterator + 'a> {`
`22`		- //~^ ERROR implementation of `FnOnce` is not general enough
	`22`	`+ //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
`23`	`23`	`Wrap(\|a\| Some(a).into_iter())`
`24`	`24`	`}`
`25`	`25`
Original file line number	Diff line number	Diff line change
`@@ -13,11 +13,16 @@ impl<'a> Hrtb<'a> for &'a () {`
`13`	`13`	`}`
`14`	`14`
`15`	`15`	`fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}`
	`16`	`+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
	`17`	`+`
`16`	`18`	`fn make_weird_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {`
`17`		- &() //~^ ERROR implementation of `Hrtb` is not general enough
	`19`	`+ //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
	`20`	`+ &()`
`18`	`21`	`}`
	`22`	`+`
`19`	`23`	`fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {`
`20`		- x //~^ ERROR implementation of `Hrtb` is not general enough
	`24`	`+ //~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
	`25`	`+ x`
`21`	`26`	`}`
`22`	`27`
`23`	`28`	`fn main() {}`
Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,3 @@`
`1`		`-// check-pass`
`2`		`-`
`3`	`1`	`// this used to cause stack overflows`
`4`	`2`
`5`	`3`	`trait Hrtb<'a> {`
`@@ -15,5 +13,6 @@ impl<'a> Hrtb<'a> for &'a () {`
`15`	`13`	`}`
`16`	`14`
`17`	`15`	`fn make_impl() -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> {}`
	`16`	`+//~^ ERROR higher kinded lifetime bounds on nested opaque types are not supported yet`
`18`	`17`
`19`	`18`	`fn main() {}`