report unconstrained region in hidden types lazily

tests/ui/traits/next-solver/opaques/eventually-constrained-region.rs

@@ -0,0 +1,21 @@
+//@ check-pass
+//@ compile-flags: -Znext-solver
+
+// Regression test for trait-system-refactor-initiative#264.
+//
+// Some defining uses of opaque types can't constrain captured regions to universals.
+// Previouly, we eagerly report error in this case.
+// Now we report error only if there's no fully defining use from all bodies of the typeck root.
+
+struct Inv<'a>(*mut &'a ());
+
+fn mk_static() -> Inv<'static> { todo!() }
+
+fn guide_closure_sig<'a>(f: impl FnOnce() -> Inv<'a>) {}
+
+fn unconstrained_in_closure() -> impl Sized {
+    guide_closure_sig(|| unconstrained_in_closure());
+    mk_static()
+}
+
+fn main() {}

tests/ui/traits/next-solver/opaques/report-all-unexpected-hidden-errors.rs

@@ -0,0 +1,34 @@
+//@ compile-flags: -Znext-solver
+
+// Just for diagnostics completeness.
+// This is probably unimportant as we only report one error for such case in HIR typeck.
+
+#![feature(type_alias_impl_trait)]
+
+struct Invar<'a>(*mut &'a ());
+
+fn mk_invar<'a>(a: &'a i32) -> Invar<'a> {
+    todo!()
+}
+
+type MultiUse = impl Sized;
+
+#[define_opaque(MultiUse)]
+fn capture_different_universals_not_on_bounds<'a, 'b, 'c>(a: &'a i32, b: &'b i32, c: &'c i32)  {
+    let _ = || -> MultiUse {
+        //~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
+        mk_invar(a)
+    };
+    let _ = || -> MultiUse {
+        //~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
+        mk_invar(b)
+    };
+    let _ = || {
+        let _ = || -> MultiUse {
+            //~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
+            mk_invar(c)
+        };
+    };
+}
+
+fn main() {}

tests/ui/traits/next-solver/opaques/report-all-unexpected-hidden-errors.stderr

@@ -0,0 +1,36 @@
+error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
+  --> $DIR/report-all-unexpected-hidden-errors.rs:18:19
+   |
+LL | type MultiUse = impl Sized;
+   |                 ---------- opaque type defined here
+...
+LL |     let _ = || -> MultiUse {
+   |                   ^^^^^^^^
+   |
+   = note: hidden type `Invar<'_>` captures lifetime `'_`
+
+error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
+  --> $DIR/report-all-unexpected-hidden-errors.rs:22:19
+   |
+LL | type MultiUse = impl Sized;
+   |                 ---------- opaque type defined here
+...
+LL |     let _ = || -> MultiUse {
+   |                   ^^^^^^^^
+   |
+   = note: hidden type `Invar<'_>` captures lifetime `'_`
+
+error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
+  --> $DIR/report-all-unexpected-hidden-errors.rs:27:23
+   |
+LL | type MultiUse = impl Sized;
+   |                 ---------- opaque type defined here
+...
+LL |         let _ = || -> MultiUse {
+   |                       ^^^^^^^^
+   |
+   = note: hidden type `Invar<'_>` captures lifetime `'_`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0700`.