lint: Improve camel case suggestion when empty.

src/librustc/lint/builtin.rs

@@ -768,9 +768,13 @@ impl LintPass for NonCamelCaseTypes {
             let s = token::get_ident(ident);
 
             if !is_camel_case(ident) {
-                cx.span_lint(NON_CAMEL_CASE_TYPES, span,
-                    format!("{} `{}` should have a camel case name such as `{}`",
-                            sort, s, to_camel_case(s.get())).as_slice());
+                let c = to_camel_case(s.get());
+                let m = if c.is_empty() {
+                    format!("{} `{}` should have a camel case name such as `CamelCase`", sort, s)
+                } else {
+                    format!("{} `{}` should have a camel case name such as `{}`", sort, s, c)
+                };
+                cx.span_lint(NON_CAMEL_CASE_TYPES, span, m.as_slice());
             }
         }
 

src/test/compile-fail/lint-non-camel-case-types.rs

@@ -37,6 +37,6 @@ struct foo7 {
     bar: int,
 }
 
-type __ = int; //~ ERROR type `__` should have a camel case name such as ``
+type __ = int; //~ ERROR type `__` should have a camel case name such as `CamelCase`
 
 fn main() { }