Rollup merge of #90750 - camelid:rm-tuple-impls-1, r=jyn514

rustdoc: Replace where-bounded Clean impl with simple function

This is the first step in removing the Clean impls for tuples. Either way, this
significantly simplifies the code since it reduces the amount of "trait magic".

(To clarify, I'm referring to impls like `impl Clean for (A, B)`, not Clean impls
that work on tuples in the user's program.)

cc ``@jyn514``

2 files changed, 33 insertions, 18 deletions

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 4a8a3160379..8f21fc5ba7f 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -229,6 +229,7 @@ fn build_external_function(cx: &mut DocContext<'_>, did: DefId) -> clean::Functi
     let asyncness = cx.tcx.asyncness(did);
     let predicates = cx.tcx.predicates_of(did);
     let (generics, decl) = clean::enter_impl_trait(cx, |cx| {
+        // NOTE: generics need to be cleaned before the decl!
         ((cx.tcx.generics_of(did), predicates).clean(cx), (did, sig).clean(cx))
     });
     clean::Function {
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 70401065689..5ca532198f4 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -109,7 +109,10 @@ impl Clean<GenericBound> for hir::GenericBound<'_> {
                 };
 
                 GenericBound::TraitBound(
-                    PolyTrait { trait_: (trait_ref, &*bindings).clean(cx), generic_params: vec![] },
+                    PolyTrait {
+                        trait_: (trait_ref, &bindings[..]).clean(cx),
+                        generic_params: vec![],
+                    },
                     hir::TraitBoundModifier::None,
                 )
             }
@@ -761,8 +764,13 @@ fn clean_fn_or_proc_macro(
 
 impl<'a> Clean<Function> for (&'a hir::FnSig<'a>, &'a hir::Generics<'a>, hir::BodyId) {
     fn clean(&self, cx: &mut DocContext<'_>) -> Function {
-        let (generics, decl) =
-            enter_impl_trait(cx, |cx| (self.1.clean(cx), (&*self.0.decl, self.2).clean(cx)));
+        let (generics, decl) = enter_impl_trait(cx, |cx| {
+            // NOTE: generics must be cleaned before args
+            let generics = self.1.clean(cx);
+            let args = (self.0.decl.inputs, self.2).clean(cx);
+            let decl = clean_fn_decl_with_args(cx, self.0.decl, args);
+            (generics, decl)
+        });
         Function { decl, generics, header: self.0.header }
     }
 }
@@ -804,17 +812,12 @@ impl<'a> Clean<Arguments> for (&'a [hir::Ty<'a>], hir::BodyId) {
     }
 }
 
-impl<'a, A: Copy> Clean<FnDecl> for (&'a hir::FnDecl<'a>, A)
-where
-    (&'a [hir::Ty<'a>], A): Clean<Arguments>,
-{
-    fn clean(&self, cx: &mut DocContext<'_>) -> FnDecl {
-        FnDecl {
-            inputs: (self.0.inputs, self.1).clean(cx),
-            output: self.0.output.clean(cx),
-            c_variadic: self.0.c_variadic,
-        }
-    }
+fn clean_fn_decl_with_args(
+    cx: &mut DocContext<'_>,
+    decl: &hir::FnDecl<'_>,
+    args: Arguments,
+) -> FnDecl {
+    FnDecl { inputs: args, output: decl.output.clean(cx), c_variadic: decl.c_variadic }
 }
 
 impl<'tcx> Clean<FnDecl> for (DefId, ty::PolyFnSig<'tcx>) {
@@ -894,7 +897,11 @@ impl Clean<Item> for hir::TraitItem<'_> {
                 }
                 hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(names)) => {
                     let (generics, decl) = enter_impl_trait(cx, |cx| {
-                        (self.generics.clean(cx), (sig.decl, names).clean(cx))
+                        // NOTE: generics must be cleaned before args
+                        let generics = self.generics.clean(cx);
+                        let args = (sig.decl.inputs, names).clean(cx);
+                        let decl = clean_fn_decl_with_args(cx, sig.decl, args);
+                        (generics, decl)
                     });
                     let mut t = Function { header: sig.header, decl, generics };
                     if t.header.constness == hir::Constness::Const
@@ -1727,8 +1734,10 @@ impl Clean<PathSegment> for hir::PathSegment<'_> {
 impl Clean<BareFunctionDecl> for hir::BareFnTy<'_> {
     fn clean(&self, cx: &mut DocContext<'_>) -> BareFunctionDecl {
         let (generic_params, decl) = enter_impl_trait(cx, |cx| {
+            // NOTE: generics must be cleaned before args
             let generic_params = self.generic_params.iter().map(|x| x.clean(cx)).collect();
-            let decl = (self.decl, self.param_names).clean(cx);
+            let args = (self.decl.inputs, self.param_names).clean(cx);
+            let decl = clean_fn_decl_with_args(cx, self.decl, args);
             (generic_params, decl)
         });
         BareFunctionDecl { unsafety: self.unsafety, abi: self.abi, decl, generic_params }
@@ -2029,8 +2038,13 @@ impl Clean<Item> for (&hir::ForeignItem<'_>, Option<Symbol>) {
             let kind = match item.kind {
                 hir::ForeignItemKind::Fn(decl, names, ref generics) => {
                     let abi = cx.tcx.hir().get_foreign_abi(item.hir_id());
-                    let (generics, decl) =
-                        enter_impl_trait(cx, |cx| (generics.clean(cx), (decl, names).clean(cx)));
+                    let (generics, decl) = enter_impl_trait(cx, |cx| {
+                        // NOTE: generics must be cleaned before args
+                        let generics = generics.clean(cx);
+                        let args = (decl.inputs, names).clean(cx);
+                        let decl = clean_fn_decl_with_args(cx, decl, args);
+                        (generics, decl)
+                    });
                     ForeignFunctionItem(Function {
                         decl,
                         generics,