Remap impl-trait lifetimes on HIR instead of AST lowering.

compiler/rustc_middle/src/query/mod.rs

@@ -1781,6 +1781,23 @@ rustc_queries! {
         -> &'tcx SortedMap<ItemLocalId, Vec<ty::BoundVariableKind>> {
         desc { |tcx| "looking up late bound vars inside `{}`", tcx.def_path_str(owner_id) }
     }
+    /// For an opaque type, return the list of (captured lifetime, inner generic param).
+    /// ```ignore (illustrative)
+    /// fn foo<'a: 'a, 'b, T>(&'b u8) -> impl Into<Self> + 'b { ... }
+    /// ```
+    ///
+    /// We would return `[('a, '_a), ('b, '_b)]`, with `'a` early-bound and `'b` late-bound.
+    ///
+    /// After hir_ty_lowering, we get:
+    /// ```ignore (pseudo-code)
+    /// opaque foo::<'a>::opaque<'_a, '_b>: Into<Foo<'_a>> + '_b;
+    ///                          ^^^^^^^^ inner generic params
+    /// fn foo<'a>: for<'b> fn(&'b u8) -> foo::<'a>::opaque::<'a, 'b>
+    ///                                                       ^^^^^^ captured lifetimes
+    /// ```
+    query opaque_captured_lifetimes(def_id: LocalDefId) -> &'tcx [(ResolvedArg, LocalDefId)] {
+        desc { |tcx| "listing captured lifetimes for opaque `{}`", tcx.def_path_str(def_id) }
+    }
 
     /// Computes the visibility of the provided `def_id`.
     ///