From 3c442b92ae2dc684e02f9668eb8c54aad55f1d9d Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <japaricious@gmail.com>
Date: Fri, 7 Nov 2014 17:16:59 -0500
Subject: [PATCH] syntax: Use UFCS in the expansion of
 `#[deriving(PartialOrd)]`

---
 src/libsyntax/ext/deriving/cmp/ord.rs | 29 +++++++++++++++++++++++----
 src/test/run-pass/issue-18738.rs      | 25 +++++++++++++++++++++++
 2 files changed, 50 insertions(+), 4 deletions(-)
 create mode 100644 src/test/run-pass/issue-18738.rs

diff --git a/src/libsyntax/ext/deriving/cmp/ord.rs b/src/libsyntax/ext/deriving/cmp/ord.rs
index 7cb61d295c0..8f3b1edb59f 100644
--- a/src/libsyntax/ext/deriving/cmp/ord.rs
+++ b/src/libsyntax/ext/deriving/cmp/ord.rs
@@ -107,12 +107,19 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt, span: Span,
     let ordering = cx.expr_path(ordering);
     let equals_expr = cx.expr_some(span, ordering);
 
+    let partial_cmp_path = vec![
+        cx.ident_of("std"),
+        cx.ident_of("cmp"),
+        cx.ident_of("PartialOrd"),
+        cx.ident_of("partial_cmp"),
+    ];
+
     /*
     Builds:
 
-    let __test = self_field1.partial_cmp(&other_field2);
+    let __test = ::std::cmp::PartialOrd::partial_cmp(&self_field1, &other_field1);
     if __test == ::std::option::Some(::std::cmp::Equal) {
-        let __test = self_field2.partial_cmp(&other_field2);
+        let __test = ::std::cmp::PartialOrd::partial_cmp(&self_field2, &other_field2);
         if __test == ::std::option::Some(::std::cmp::Equal) {
             ...
         } else {
@@ -124,11 +131,11 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt, span: Span,
 
     FIXME #6449: These `if`s could/should be `match`es.
     */
-    cs_same_method_fold(
+    cs_fold(
         // foldr nests the if-elses correctly, leaving the first field
         // as the outermost one, and the last as the innermost.
         false,
-        |cx, span, old, new| {
+        |cx, span, old, self_f, other_fs| {
             // let __test = new;
             // if __test == Some(::std::cmp::Equal) {
             //    old
@@ -136,6 +143,20 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt, span: Span,
             //    __test
             // }
 
+            let new = {
+                let other_f = match other_fs {
+                    [ref o_f] => o_f,
+                    _ => cx.span_bug(span, "not exactly 2 arguments in `deriving(Ord)`"),
+                };
+
+                let args = vec![
+                    cx.expr_addr_of(span, self_f),
+                    cx.expr_addr_of(span, other_f.clone()),
+                ];
+
+                cx.expr_call_global(span, partial_cmp_path.clone(), args)
+            };
+
             let assign = cx.stmt_let(span, false, test_id, new);
 
             let cond = cx.expr_binary(span, ast::BiEq,
diff --git a/src/test/run-pass/issue-18738.rs b/src/test/run-pass/issue-18738.rs
new file mode 100644
index 00000000000..7958b9ec117
--- /dev/null
+++ b/src/test/run-pass/issue-18738.rs
@@ -0,0 +1,25 @@
+// Copyright 2014 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.
+
+#[deriving(PartialEq, PartialOrd)]
+enum Test<'a> {
+    Int(&'a int),
+    Slice(&'a [u8]),
+}
+
+#[deriving(PartialEq, PartialOrd)]
+struct Version {
+    vendor_info: &'static str
+}
+
+#[deriving(PartialEq, PartialOrd)]
+struct Foo(&'static str);
+
+fn main() {}