std::fmt: prepare to convert the formatting traits to methods, and work

around the lack of UFCS.

The further work is pending a snapshot, to avoid putting #[cfg(stage0)]
attributes on all the traits and duplicating them.

Author: huonw

src/libstd/fmt/mod.rs

@@ -606,6 +606,41 @@ pub trait LowerExp { fn fmt(&Self, &mut Formatter); }
 #[allow(missing_doc)]
 pub trait UpperExp { fn fmt(&Self, &mut Formatter); }
 
+// FIXME #11938 - UFCS would make us able call the above methods
+// directly Show::show(x, fmt).
+
+// FIXME(huonw's WIP): this is a intermediate state waiting for a
+// snapshot (at the time of writing we're at 2014-01-20 b6400f9), to
+// be able to make the `fmt` functions into normal methods and have
+// `format!()` still work.
+macro_rules! uniform_fn_call_workaround {
+    ($( $name: ident, $trait_: ident; )*) => {
+        $(
+            #[doc(hidden)]
+            pub fn $name<T: $trait_>(x: &T, fmt: &mut Formatter) {
+                $trait_::fmt(x, fmt)
+            }
+            )*
+    }
+}
+uniform_fn_call_workaround! {
+    secret_show, Show;
+    secret_bool, Bool;
+    secret_char, Char;
+    secret_signed, Signed;
+    secret_unsigned, Unsigned;
+    secret_octal, Octal;
+    secret_binary, Binary;
+    secret_lower_hex, LowerHex;
+    secret_upper_hex, UpperHex;
+    secret_string, String;
+    secret_poly, Poly;
+    secret_pointer, Pointer;
+    secret_float, Float;
+    secret_lower_exp, LowerExp;
+    secret_upper_exp, UpperExp;
+}
+
 /// The `write` function takes an output stream, a precompiled format string,
 /// and a list of arguments. The arguments will be formatted according to the
 /// specified format string into the output stream provided.

src/libsyntax/ext/format.rs

@@ -702,7 +702,7 @@ impl<'a> Context<'a> {
             Named(ref s) => self.name_types.get(s)
         };
 
-        let fmt_trait = match *ty {
+        let fmt_fn = match *ty {
             Known(ref tyname) => {
                 match tyname.as_slice() {
                     ""  => "secret_show",
@@ -721,10 +721,9 @@ impl<'a> Context<'a> {
                     "x" => "secret_lower_hex",
                     "X" => "secret_upper_hex",
                     _ => {
-                        self.ecx.span_err(sp,
-                                          format!("unknown format trait `{}`",
-                                                  *tyname));
-                        "Dummy"
+                        self.ecx.span_err(sp, format!("unknown format trait `{}`",
+                                                      *tyname));
+                        "dummy"
                     }
                 }
             }
@@ -747,8 +746,7 @@ impl<'a> Context<'a> {
         let format_fn = self.ecx.path_global(sp, ~[
                 self.ecx.ident_of("std"),
                 self.ecx.ident_of("fmt"),
-                self.ecx.ident_of(fmt_trait),
-                self.ecx.ident_of("fmt"),
+                self.ecx.ident_of(fmt_fn),
             ]);
         self.ecx.expr_call_global(sp, ~[
                 self.ecx.ident_of("std"),