auto merge of #9535 : alexcrichton/rust/no-format-default, r=thestinger

As mentioned in #9456, the format! syntax extension would previously consider an
empty format as a 'Unknown' format which could then also get coerced into a
different style of format on another argument.

This is unusual behavior because `{}` is a very common format and if you have
`{0} {0:?}` you wouldn't expect them both to be coereced to the `Poly`
formatter. This commit removes this coercion, but still retains the requirement
that each argument has exactly one format specified for it (an empty format now
counts as well).

Perhaps at a later date we can add support for multiple formats of one argument,
but this puts us in at least a backwards-compatible situation if we decide to do
that.

src/librustdoc/html/render.rs

@@ -1159,11 +1159,12 @@ impl<'self> fmt::Default for Sidebar<'self> {
                 write!(w, "<a class='{ty} {class}' href='{curty, select,
                                 mod{../}
                                 other{}
-                           }{ty, select,
+                           }{tysel, select,
                                 mod{{name}/index.html}
                                 other{#.{name}.html}
                            }'>{name}</a><br/>",
                        ty = short,
+                       tysel = short,
                        class = class,
                        curty = shortty(cur),
                        name = item.as_slice());

src/libsyntax/ext/format.rs

@@ -22,7 +22,6 @@ use std::vec;
 
 #[deriving(Eq)]
 enum ArgumentType {
-    Unknown,
     Known(@str),
     Unsigned,
     String,
@@ -153,14 +152,13 @@ impl Context {
                     parse::ArgumentIs(i) => Left(i),
                     parse::ArgumentNamed(s) => Right(s.to_managed()),
                 };
-                let ty = if arg.format.ty == "" {
-                    Unknown
-                } else { Known(arg.format.ty.to_managed()) };
-                self.verify_arg_type(pos, ty);
 
                 // and finally the method being applied
                 match arg.method {
-                    None => {}
+                    None => {
+                        let ty = Known(arg.format.ty.to_managed());
+                        self.verify_arg_type(pos, ty);
+                    }
                     Some(ref method) => { self.verify_method(pos, *method); }
                 }
             }
@@ -253,7 +251,7 @@ impl Context {
                     return;
                 }
                 self.verify_same(self.args[arg].span, ty, self.arg_types[arg]);
-                if ty != Unknown || self.arg_types[arg].is_none() {
+                if self.arg_types[arg].is_none() {
                     self.arg_types[arg] = Some(ty);
                 }
             }
@@ -269,7 +267,7 @@ impl Context {
                 };
                 self.verify_same(span, ty,
                                  self.name_types.find(&name).map(|&x| *x));
-                if ty != Unknown || !self.name_types.contains_key(&name) {
+                if !self.name_types.contains_key(&name) {
                     self.name_types.insert(name, ty);
                 }
                 // Assign this named argument a slot in the arguments array if
@@ -292,9 +290,8 @@ impl Context {
     /// that: `Some(None) == Some(Some(x))`
     fn verify_same(&self, sp: Span, ty: ArgumentType,
                    before: Option<ArgumentType>) {
-        if ty == Unknown { return }
         let cur = match before {
-            Some(Unknown) | None => return,
+            None => return,
             Some(t) => t,
         };
         if ty == cur { return }
@@ -649,9 +646,9 @@ impl Context {
         };
 
         let fmt_trait = match ty {
-            Unknown => "Default",
             Known(tyname) => {
                 match tyname.as_slice() {
+                    ""  => "Default",
                     "?" => "Poly",
                     "b" => "Bool",
                     "c" => "Char",

src/test/compile-fail/ifmt-bad-arg.rs

@@ -65,8 +65,8 @@ fn main() {
     // format strings because otherwise the "internal pointer of which argument
     // is next" would be invalidated if different cases had different numbers of
     // arguments.
-    format!("{0, select, other{{}}}", "a"); //~ ERROR: cannot use implicit
-    format!("{0, plural, other{{}}}", 1); //~ ERROR: cannot use implicit
+    format!("{1, select, other{{}}}", 1, "a"); //~ ERROR: cannot use implicit
+    format!("{1, plural, other{{}}}", 1, 1); //~ ERROR: cannot use implicit
     format!("{0, plural, other{{1:.*d}}}", 1, 2); //~ ERROR: cannot use implicit
 
     format!("foo } bar"); //~ ERROR: unmatched `}` found

src/test/run-pass/ifmt.rs

@@ -85,7 +85,6 @@ pub fn main() {
     t!(format!("{1} {0}", 0, 1), "1 0");
     t!(format!("{foo} {bar}", foo=0, bar=1), "0 1");
     t!(format!("{foo} {1} {bar} {0}", 0, 1, foo=2, bar=3), "2 1 3 0");
-    t!(format!("{} {0:s}", "a"), "a a");
     t!(format!("{} {0}", "a"), "a a");
     t!(format!("{foo_bar}", foo_bar=1), "1");
 
@@ -98,8 +97,8 @@ pub fn main() {
     t!(format!("{0, select, a{a#} b{b#} c{c#} other{d#}}", "b"), "bb");
     t!(format!("{0, select, a{a#} b{b#} c{c#} other{d#}}", "c"), "cc");
     t!(format!("{0, select, a{a#} b{b#} c{c#} other{d#}}", "d"), "dd");
-    t!(format!("{1, select, a{#{0:s}} other{#{1}}}", "b", "a"), "ab");
-    t!(format!("{1, select, a{#{0}} other{#{1}}}", "c", "b"), "bb");
+    t!(format!("{1, select, a{#{0:s}} other{#}}", "b", "a"), "ab");
+    t!(format!("{1, select, a{#{0}} other{#}}", "c", "b"), "b");
 
     // Formatting strings and their arguments
     t!(format!("{:s}", "a"), "a");