Rollup merge of #116039 - estebank:nested-tait, r=compiler-errors

Account for nested `impl Trait` in TAIT

Fix #116031.

r? `@compiler-errors`

2 files changed, 56 insertions, 0 deletions

diff --git a/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.rs b/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.rs
new file mode 100644
index 00000000000..fec0fdc46fb
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.rs
@@ -0,0 +1,9 @@
+#![feature(type_alias_impl_trait)]
+
+pub type Tait = impl Iterator<Item = (&'db Key, impl Iterator)>;
+//~^ ERROR use of undeclared lifetime name `'db`
+//~| ERROR cannot find type `Key` in this scope
+//~| ERROR unconstrained opaque type
+//~| ERROR unconstrained opaque type
+
+pub fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.stderr b/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.stderr
new file mode 100644
index 00000000000..d4aeace4ae7
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/nested-impl-trait-in-tait.stderr
@@ -0,0 +1,47 @@
+error[E0261]: use of undeclared lifetime name `'db`
+  --> $DIR/nested-impl-trait-in-tait.rs:3:40
+   |
+LL | pub type Tait = impl Iterator<Item = (&'db Key, impl Iterator)>;
+   |                                        ^^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'db` lifetime
+   |
+LL | pub type Tait = impl for<'db> Iterator<Item = (&'db Key, impl Iterator)>;
+   |                      ++++++++
+help: consider introducing lifetime `'db` here
+   |
+LL | pub type Tait<'db> = impl Iterator<Item = (&'db Key, impl Iterator)>;
+   |              +++++
+
+error[E0412]: cannot find type `Key` in this scope
+  --> $DIR/nested-impl-trait-in-tait.rs:3:44
+   |
+LL | pub type Tait = impl Iterator<Item = (&'db Key, impl Iterator)>;
+   |                                            ^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::thread::local_impl::Key;
+   |
+
+error: unconstrained opaque type
+  --> $DIR/nested-impl-trait-in-tait.rs:3:17
+   |
+LL | pub type Tait = impl Iterator<Item = (&'db Key, impl Iterator)>;
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `Tait` must be used in combination with a concrete type within the same module
+
+error: unconstrained opaque type
+  --> $DIR/nested-impl-trait-in-tait.rs:3:49
+   |
+LL | pub type Tait = impl Iterator<Item = (&'db Key, impl Iterator)>;
+   |                                                 ^^^^^^^^^^^^^
+   |
+   = note: `Tait` must be used in combination with a concrete type within the same module
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0261, E0412.
+For more information about an error, try `rustc --explain E0261`.