From 5965af701090591edad308e9877d72bbe2221b48 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Le=C3=B3n=20Orell=20Valerian=20Liehr?=
 <liehr.exchange@gmx.net>
Date: Wed, 2 Nov 2022 15:10:36 +0100
Subject: [PATCH] rustdoc: render late-bound lifetimes in generic parameter
 list of cross-crate functions and methods

---
 src/librustdoc/clean/inline.rs   | 16 ++++++++++++++--
 src/librustdoc/clean/mod.rs      | 20 ++++++++++++++++++--
 src/librustdoc/clean/simplify.rs |  5 ++---
 src/test/rustdoc/issue-20727.rs  |  2 +-
 4 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 841c4f9d530..bfbe143c202 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -243,10 +243,22 @@ pub(crate) fn build_external_trait(cx: &mut DocContext<'_>, did: DefId) -> clean
 fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> Box<clean::Function> {
     let sig = cx.tcx.fn_sig(did);
 
-    let predicates = cx.tcx.predicates_of(did);
+    let late_bound_regions = sig.bound_vars().into_iter().filter_map(|var| match var {
+        ty::BoundVariableKind::Region(ty::BrNamed(_, name)) if name != kw::UnderscoreLifetime => {
+            Some(clean::GenericParamDef {
+                name,
+                kind: clean::GenericParamDefKind::Lifetime { outlives: Vec::new() },
+            })
+        }
+        _ => None,
+    });
+
+    let predicates = cx.tcx.explicit_predicates_of(did);
     let (generics, decl) = clean::enter_impl_trait(cx, |cx| {
         // NOTE: generics need to be cleaned before the decl!
-        let generics = clean_ty_generics(cx, cx.tcx.generics_of(did), predicates);
+        let mut generics = clean_ty_generics(cx, cx.tcx.generics_of(did), predicates);
+        // FIXME: This does not place parameters in source order (late-bound ones come last)
+        generics.params.extend(late_bound_regions);
         let decl = clean_fn_decl_from_did_and_sig(cx, Some(did), sig);
         (generics, decl)
     });
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 8d38f2df0d8..a179bd3c39f 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1144,12 +1144,28 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
             }
         }
         ty::AssocKind::Fn => {
-            let generics = clean_ty_generics(
+            let sig = tcx.fn_sig(assoc_item.def_id);
+
+            let late_bound_regions = sig.bound_vars().into_iter().filter_map(|var| match var {
+                ty::BoundVariableKind::Region(ty::BrNamed(_, name))
+                    if name != kw::UnderscoreLifetime =>
+                {
+                    Some(GenericParamDef {
+                        name,
+                        kind: GenericParamDefKind::Lifetime { outlives: Vec::new() },
+                    })
+                }
+                _ => None,
+            });
+
+            let mut generics = clean_ty_generics(
                 cx,
                 tcx.generics_of(assoc_item.def_id),
                 tcx.explicit_predicates_of(assoc_item.def_id),
             );
-            let sig = tcx.fn_sig(assoc_item.def_id);
+            // FIXME: This does not place parameters in source order (late-bound ones come last)
+            generics.params.extend(late_bound_regions);
+
             let mut decl = clean_fn_decl_from_did_and_sig(cx, Some(assoc_item.def_id), sig);
 
             if assoc_item.fn_has_self_parameter {
diff --git a/src/librustdoc/clean/simplify.rs b/src/librustdoc/clean/simplify.rs
index 1c184f9b269..cd9dab1b1d5 100644
--- a/src/librustdoc/clean/simplify.rs
+++ b/src/librustdoc/clean/simplify.rs
@@ -99,9 +99,8 @@ pub(crate) fn merge_bounds(
         let last = trait_ref.trait_.segments.last_mut().expect("segments were empty");
 
         trait_ref.generic_params.append(&mut bound_params);
-        // Since the parameters (probably) originate from `tcx.collect_*_late_bound_regions` which
-        // returns a hash set, sort them alphabetically to guarantee a stable and deterministic
-        // output (and to fully deduplicate them).
+        // Sort parameters (likely) originating from a hashset alphabetically to
+        // produce predictable output (and to allow for full deduplication).
         trait_ref.generic_params.sort_unstable_by(|p, q| p.name.as_str().cmp(q.name.as_str()));
         trait_ref.generic_params.dedup_by_key(|p| p.name);
 
diff --git a/src/test/rustdoc/issue-20727.rs b/src/test/rustdoc/issue-20727.rs
index f7acffcb4e5..c1a98cd57da 100644
--- a/src/test/rustdoc/issue-20727.rs
+++ b/src/test/rustdoc/issue-20727.rs
@@ -19,6 +19,6 @@ pub mod reexport {
     // @has - '//*[@class="rust trait"]' 'trait Deref {'
     // @has - '//*[@class="rust trait"]' 'type Target: ?Sized;'
     // @has - '//*[@class="rust trait"]' \
-    //      "fn deref(&'a self) -> &'a Self::Target;"
+    //      "fn deref<'a>(&'a self) -> &'a Self::Target;"
     pub use issue_20727::Deref;
 }