Auto merge of #44892 - GuillaumeGomez:fnty-args-rustdoc, r=eddyb

Fnty args rustdoc

Fixes #44570.

cc @QuietMisdreavus
cc @rust-lang/dev-tools

Considering the impact on the `hir` libs, I'll put @eddyb as reviewer.

r? @eddyb

src/librustc/hir/lowering.rs

@@ -673,6 +673,7 @@ impl<'a> LoweringContext<'a> {
                     unsafety: self.lower_unsafety(f.unsafety),
                     abi: f.abi,
                     decl: self.lower_fn_decl(&f.decl),
+                    arg_names: self.lower_fn_args_to_names(&f.decl),
                 }))
             }
             TyKind::Never => hir::TyNever,

src/librustc/hir/mod.rs

@@ -1418,6 +1418,7 @@ pub struct BareFnTy {
     pub abi: Abi,
     pub lifetimes: HirVec<LifetimeDef>,
     pub decl: P<FnDecl>,
+    pub arg_names: HirVec<Spanned<Name>>,
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]

src/librustc/hir/print.rs

@@ -399,7 +399,8 @@ impl<'a> State<'a> {
                     },
                     span: syntax_pos::DUMMY_SP,
                 };
-                self.print_ty_fn(f.abi, f.unsafety, &f.decl, None, &generics)?;
+                self.print_ty_fn(f.abi, f.unsafety, &f.decl, None, &generics,
+                                 &f.arg_names[..])?;
             }
             hir::TyPath(ref qpath) => {
                 self.print_qpath(qpath, false)?
@@ -2140,7 +2141,8 @@ impl<'a> State<'a> {
                        unsafety: hir::Unsafety,
                        decl: &hir::FnDecl,
                        name: Option<ast::Name>,
-                       generics: &hir::Generics)
+                       generics: &hir::Generics,
+                       arg_names: &[Spanned<ast::Name>])
                        -> io::Result<()> {
         self.ibox(indent_unit)?;
         if !generics.lifetimes.is_empty() || !generics.ty_params.is_empty() {
@@ -2163,7 +2165,7 @@ impl<'a> State<'a> {
                       name,
                       &generics,
                       &hir::Inherited,
-                      &[],
+                      arg_names,
                       None)?;
         self.end()
     }

src/librustc/ich/impls_hir.rs

@@ -274,7 +274,8 @@ impl_stable_hash_for!(struct hir::BareFnTy {
     unsafety,
     abi,
     lifetimes,
-    decl
+    decl,
+    arg_names
 });
 
 impl_stable_hash_for!(enum hir::Ty_ {

src/librustdoc/clean/mod.rs

@@ -2491,7 +2491,7 @@ impl Clean<BareFunctionDecl> for hir::BareFnTy {
                 type_params: Vec::new(),
                 where_predicates: Vec::new()
             },
-            decl: (&*self.decl, &[][..]).clean(cx),
+            decl: (&*self.decl, &self.arg_names[..]).clean(cx),
             abi: self.abi,
         }
     }

src/test/rustdoc/fn-pointer-arg-name.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![crate_name = "foo"]
+
+// @has foo/fn.f.html
+// @has - '//*[@class="rust fn"]' 'pub fn f(callback: fn(len: usize, foo: u32))'
+pub fn f(callback: fn(len: usize, foo: u32)) {}