From 199eacaa7d21ccc28d7afef552ed42df1895afac Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 11 Jul 2024 19:49:51 -0400
Subject: [PATCH] Add rustdoc support for use<> in (local) RPITs

---
 compiler/rustc_hir/src/hir.rs                 |  7 +++++++
 src/librustdoc/clean/mod.rs                   |  5 +++--
 src/librustdoc/clean/simplify.rs              |  2 +-
 src/librustdoc/clean/types.rs                 |  2 ++
 src/librustdoc/html/format.rs                 | 14 ++++++++++++++
 tests/rustdoc/impl-trait-precise-capturing.rs | 14 ++++++++++++++
 6 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 tests/rustdoc/impl-trait-precise-capturing.rs

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index d57fad6ba4c2d..4561f9d9b49df 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2708,6 +2708,13 @@ impl PreciseCapturingArg<'_> {
             PreciseCapturingArg::Param(param) => param.hir_id,
         }
     }
+
+    pub fn name(self) -> Symbol {
+        match self {
+            PreciseCapturingArg::Lifetime(lt) => lt.ident.name,
+            PreciseCapturingArg::Param(param) => param.ident.name,
+        }
+    }
 }
 
 /// We need to have a [`Node`] for the [`HirId`] that we attach the type/const param
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index aa596897fc42f..98ce268a77466 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -228,8 +228,9 @@ fn clean_generic_bound<'tcx>(
 
             GenericBound::TraitBound(clean_poly_trait_ref(t, cx), modifier)
         }
-        // FIXME(precise_capturing): Implement rustdoc support
-        hir::GenericBound::Use(..) => return None,
+        hir::GenericBound::Use(args, ..) => {
+            GenericBound::Use(args.iter().map(|arg| arg.name()).collect())
+        }
     })
 }
 
diff --git a/src/librustdoc/clean/simplify.rs b/src/librustdoc/clean/simplify.rs
index 58eef36677b23..1b7d84add1f85 100644
--- a/src/librustdoc/clean/simplify.rs
+++ b/src/librustdoc/clean/simplify.rs
@@ -79,7 +79,7 @@ pub(crate) fn merge_bounds(
     !bounds.iter_mut().any(|b| {
         let trait_ref = match *b {
             clean::GenericBound::TraitBound(ref mut tr, _) => tr,
-            clean::GenericBound::Outlives(..) => return false,
+            clean::GenericBound::Outlives(..) | clean::GenericBound::Use(_) => return false,
         };
         // If this QPath's trait `trait_did` is the same as, or a supertrait
         // of, the bound's trait `did` then we can keep going, otherwise
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index fe01d17b08a8c..a31adc9949a3f 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -1244,6 +1244,8 @@ impl Eq for Attributes {}
 pub(crate) enum GenericBound {
     TraitBound(PolyTrait, hir::TraitBoundModifier),
     Outlives(Lifetime),
+    /// `use<'a, T>` precise-capturing bound syntax
+    Use(Vec<Symbol>),
 }
 
 impl GenericBound {
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 4268fadd6c59c..e811e0bf537ad 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -412,6 +412,20 @@ impl clean::GenericBound {
                 })?;
                 ty.print(cx).fmt(f)
             }
+            clean::GenericBound::Use(args) => {
+                if f.alternate() {
+                    f.write_str("use&lt;")?;
+                } else {
+                    f.write_str("use<")?;
+                }
+                for (i, arg) in args.iter().enumerate() {
+                    if i > 0 {
+                        write!(f, ", ")?;
+                    }
+                    arg.fmt(f)?;
+                }
+                if f.alternate() { f.write_str("&gt;") } else { f.write_str(">") }
+            }
         })
     }
 }
diff --git a/tests/rustdoc/impl-trait-precise-capturing.rs b/tests/rustdoc/impl-trait-precise-capturing.rs
new file mode 100644
index 0000000000000..d1987a555c151
--- /dev/null
+++ b/tests/rustdoc/impl-trait-precise-capturing.rs
@@ -0,0 +1,14 @@
+#![crate_name = "foo"]
+#![feature(precise_capturing)]
+
+//@ has foo/fn.two.html '//section[@id="main-content"]//pre' "-> impl Sized + use<'b, 'a>"
+pub fn two<'a, 'b, 'c>() -> impl Sized + use<'b, 'a /* no 'c */> {}
+
+//@ has foo/fn.params.html '//section[@id="main-content"]//pre' "-> impl Sized + use<'a, T, N>"
+pub fn params<'a, T, const N: usize>() -> impl Sized + use<'a, T, N> {}
+
+//@ has foo/fn.none.html '//section[@id="main-content"]//pre' "-> impl Sized + use<>"
+pub fn none() -> impl Sized + use<> {}
+
+//@ has foo/fn.first.html '//section[@id="main-content"]//pre' "-> impl use<> + Sized"
+pub fn first() -> impl use<> + Sized {}