Restructure debug builders to minimize codegen

Switching from generic bounds to trait objects and having un-inlined
inner methods should cut down on the size of Debug impls, since we care
about the speed of a Debug implementation way less than binary bloat.

Author: sfackler

src/libcore/fmt/builders.rs

@@ -63,8 +63,13 @@ pub fn debug_struct_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str)
 impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
     /// Adds a new field to the generated struct output.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn field<S>(mut self, name: &str, value: &S) -> DebugStruct<'a, 'b>
-            where S: fmt::Debug {
+    #[inline]
+    pub fn field(mut self, name: &str, value: &fmt::Debug) -> DebugStruct<'a, 'b> {
+        self.field_inner(name, value);
+        self
+    }
+
+    fn field_inner(&mut self, name: &str, value: &fmt::Debug) {
         self.result = self.result.and_then(|_| {
             let prefix = if self.has_fields {
                 ","
@@ -81,13 +86,18 @@ impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
         });
 
         self.has_fields = true;
-        self
     }
 
     /// Consumes the `DebugStruct`, finishing output and returning any error
     /// encountered.
     #[unstable(feature = "core", reason = "method was just created")]
+    #[inline]
     pub fn finish(mut self) -> fmt::Result {
+        self.finish_inner();
+        self.result
+    }
+
+    fn finish_inner(&mut self) {
         if self.has_fields {
             self.result = self.result.and_then(|_| {
                 if self.is_pretty() {
@@ -97,7 +107,6 @@ impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
                 }
             });
         }
-        self.result
     }
 
     fn is_pretty(&self) -> bool {
@@ -127,7 +136,13 @@ pub fn debug_tuple_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> D
 impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
     /// Adds a new field to the generated tuple struct output.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn field<S>(mut self, value: &S) -> DebugTuple<'a, 'b> where S: fmt::Debug {
+    #[inline]
+    pub fn field(mut self, value: &fmt::Debug) -> DebugTuple<'a, 'b> {
+        self.field_inner(value);
+        self
+    }
+
+    fn field_inner(&mut self, value: &fmt::Debug) {
         self.result = self.result.and_then(|_| {
             let (prefix, space) = if self.has_fields {
                 (",", " ")
@@ -144,13 +159,18 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
         });
 
         self.has_fields = true;
-        self
     }
 
     /// Consumes the `DebugTuple`, finishing output and returning any error
     /// encountered.
     #[unstable(feature = "core", reason = "method was just created")]
+    #[inline]
     pub fn finish(mut self) -> fmt::Result {
+        self.finish_inner();
+        self.result
+    }
+
+    fn finish_inner(&mut self) {
         if self.has_fields {
             self.result = self.result.and_then(|_| {
                 if self.is_pretty() {
@@ -160,7 +180,6 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
                 }
             });
         }
-        self.result
     }
 
     fn is_pretty(&self) -> bool {
@@ -190,7 +209,13 @@ pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> Deb
 impl<'a, 'b: 'a> DebugSet<'a, 'b> {
     /// Adds a new entry to the set output.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn entry<S>(mut self, entry: &S) -> DebugSet<'a, 'b> where S: fmt::Debug {
+    #[inline]
+    pub fn entry(mut self, entry: &fmt::Debug) -> DebugSet<'a, 'b> {
+        self.entry_inner(entry);
+        self
+    }
+
+    fn entry_inner(&mut self, entry: &fmt::Debug) {
         self.result = self.result.and_then(|_| {
             let prefix = if self.has_fields {
                 ","
@@ -207,21 +232,26 @@ impl<'a, 'b: 'a> DebugSet<'a, 'b> {
         });
 
         self.has_fields = true;
-        self
     }
 
     /// Consumes the `DebugSet`, finishing output and returning any error
     /// encountered.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn finish(self) -> fmt::Result {
-        self.result.and_then(|_| {
+    #[inline]
+    pub fn finish(mut self) -> fmt::Result {
+        self.finish_inner();
+        self.result
+    }
+
+    fn finish_inner(&mut self) {
+        self.result = self.result.and_then(|_| {
             let end = match (self.has_fields, self.is_pretty()) {
                 (false, _) => "}",
                 (true, false) => " }",
                 (true, true) => "\n}",
             };
             self.fmt.write_str(end)
-        })
+        });
     }
 
     fn is_pretty(&self) -> bool {
@@ -251,8 +281,13 @@ pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> Deb
 impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     /// Adds a new entry to the map output.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn entry<K, V>(mut self, key: &K, value: &V) -> DebugMap<'a, 'b>
-            where K: fmt::Debug, V: fmt::Debug {
+    #[inline]
+    pub fn entry(mut self, key: &fmt::Debug, value: &fmt::Debug) -> DebugMap<'a, 'b> {
+        self.entry_inner(key, value);
+        self
+    }
+
+    fn entry_inner(&mut self, key: &fmt::Debug, value: &fmt::Debug) {
         self.result = self.result.and_then(|_| {
             let prefix = if self.has_fields {
                 ","
@@ -269,21 +304,26 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
         });
 
         self.has_fields = true;
-        self
     }
 
     /// Consumes the `DebugMap`, finishing output and returning any error
     /// encountered.
     #[unstable(feature = "core", reason = "method was just created")]
-    pub fn finish(self) -> fmt::Result {
-        self.result.and_then(|_| {
+    #[inline]
+    pub fn finish(mut self) -> fmt::Result {
+        self.finish_inner();
+        self.result
+    }
+
+    fn finish_inner(&mut self) {
+        self.result = self.result.and_then(|_| {
             let end = match (self.has_fields, self.is_pretty()) {
                 (false, _) => "}",
                 (true, false) => " }",
                 (true, true) => "\n}",
             };
             self.fmt.write_str(end)
-        })
+        });
     }
 
     fn is_pretty(&self) -> bool {