Auto merge of #27919 - Eljay:doc-varargs, r=alexcrichton

Fixes #27876.

src/librustdoc/clean/mod.rs

@@ -999,6 +999,7 @@ impl Clean<Method> for ast::MethodSig {
                 values: inputs.clean(cx),
             },
             output: self.decl.output.clean(cx),
+            variadic: false,
             attrs: Vec::new()
         };
         Method {
@@ -1032,6 +1033,7 @@ impl Clean<TyMethod> for ast::MethodSig {
                 values: inputs.clean(cx),
             },
             output: self.decl.output.clean(cx),
+            variadic: false,
             attrs: Vec::new()
         };
         TyMethod {
@@ -1098,6 +1100,7 @@ impl Clean<Item> for doctree::Function {
 pub struct FnDecl {
     pub inputs: Arguments,
     pub output: FunctionRetTy,
+    pub variadic: bool,
     pub attrs: Vec<Attribute>,
 }
 
@@ -1113,6 +1116,7 @@ impl Clean<FnDecl> for ast::FnDecl {
                 values: self.inputs.clean(cx),
             },
             output: self.output.clean(cx),
+            variadic: self.variadic,
             attrs: Vec::new()
         }
     }
@@ -1141,6 +1145,7 @@ impl<'a, 'tcx> Clean<FnDecl> for (ast::DefId, &'a ty::PolyFnSig<'tcx>) {
         FnDecl {
             output: Return(sig.0.output.clean(cx)),
             attrs: Vec::new(),
+            variadic: sig.0.variadic,
             inputs: Arguments {
                 values: sig.0.inputs.iter().map(|t| {
                     Argument {

src/librustdoc/html/format.rs

@@ -579,9 +579,13 @@ impl fmt::Display for clean::FunctionRetTy {
 
 impl fmt::Display for clean::FnDecl {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.variadic {
+            write!(f, "({args}, ...){arrow}", args = self.inputs, arrow = self.output)
+        } else {
             write!(f, "({args}){arrow}", args = self.inputs, arrow = self.output)
         }
     }
+}
 
 impl<'a> fmt::Display for Method<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

src/test/rustdoc/variadic.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+extern "C" {
+    // @has variadic/fn.foo.html //pre 'pub unsafe extern fn foo(x: i32, ...)'
+    pub fn foo(x: i32, ...);
+}