Print variadic argument pattern in HIR pretty printer

compiler/rustc_ast_lowering/src/lib.rs

@@ -1737,14 +1737,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
-        // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
-        // as they are not explicit in HIR/Ty function signatures.
-        // (instead, the `c_variadic` flag is set to `true`)
-        let mut inputs = &decl.inputs[..];
-        if decl.c_variadic() {
-            inputs = &inputs[..inputs.len() - 1];
-        }
-        self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
+        self.arena.alloc_from_iter(decl.inputs.iter().map(|param| match param.pat.kind {
             PatKind::Ident(_, ident, _) => self.lower_ident(ident),
             _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
         }))

compiler/rustc_hir_pretty/src/lib.rs

@@ -502,13 +502,13 @@ impl<'a> State<'a> {
                 self.word(";");
                 self.end(); // end the outer cbox
             }
-            hir::ItemKind::Fn(ref sig, param_names, body) => {
+            hir::ItemKind::Fn(ref sig, generics, body) => {
                 self.head("");
                 self.print_fn(
                     sig.decl,
                     sig.header,
                     Some(item.ident.name),
-                    param_names,
+                    generics,
                     &[],
                     Some(body),
                 );
@@ -1948,11 +1948,10 @@ impl<'a> State<'a> {
         self.print_generic_params(generics.params);
 
         self.popen();
-        let mut i = 0;
         // Make sure we aren't supplied *both* `arg_names` and `body_id`.
         assert!(arg_names.is_empty() || body_id.is_none());
-        self.commasep(Inconsistent, decl.inputs, |s, ty| {
-            s.ibox(INDENT_UNIT);
+        let mut i = 0;
+        let mut print_arg = |s: &mut Self| {
             if let Some(arg_name) = arg_names.get(i) {
                 s.word(arg_name.to_string());
                 s.word(":");
@@ -1963,11 +1962,17 @@ impl<'a> State<'a> {
                 s.space();
             }
             i += 1;
+        };
+        self.commasep(Inconsistent, decl.inputs, |s, ty| {
+            s.ibox(INDENT_UNIT);
+            print_arg(s);
             s.print_type(ty);
-            s.end()
+            s.end();
         });
         if decl.c_variadic {
-            self.word(", ...");
+            self.word(", ");
+            print_arg(self);
+            self.word("...");
         }
         self.pclose();
 

tests/pretty/hir-fn-variadic.pp

@@ -0,0 +1,15 @@
+// pretty-compare-only
+// pretty-mode:hir
+// pp-exact:hir-fn-variadic.pp
+
+#![feature(c_variadic)]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+
+extern "C" {
+    fn foo(x: i32, va1: ...);
+}
+
+unsafe extern "C" fn bar(_: i32, mut va2: ...) -> usize { va2.arg::<usize>() }

tests/pretty/hir-fn-variadic.rs

@@ -0,0 +1,13 @@
+// pretty-compare-only
+// pretty-mode:hir
+// pp-exact:hir-fn-variadic.pp
+
+#![feature(c_variadic)]
+
+extern "C" {
+    pub fn foo(x: i32, va1: ...);
+}
+
+pub unsafe extern "C" fn bar(_: i32, mut va2: ...) -> usize {
+    va2.arg::<usize>()
+}