lint: Allow trailing underscores in camel case idents

src/rustc/middle/lint.rs

@@ -452,10 +452,21 @@ fn check_item_path_statement(cx: ty::ctxt, it: @ast::item) {
 fn check_item_non_camel_case_types(cx: ty::ctxt, it: @ast::item) {
     fn is_camel_case(ident: ast::ident) -> bool {
         assert ident.is_not_empty();
-        char::is_uppercase(str::char_at(*ident, 0)) &&
+        let ident = ident_without_trailing_underscores(ident);
+        char::is_uppercase(str::char_at(ident, 0)) &&
             !ident.contains_char('_')
     }
 
+    fn ident_without_trailing_underscores(ident: ast::ident) -> ~str {
+        match str::rfind(*ident, |c| c != '_') {
+          some(idx) => (*ident).slice(0, idx + 1),
+          none => {
+            // all underscores
+            *ident
+          }
+        }
+    }
+
     fn check_case(cx: ty::ctxt, ident: ast::ident,
                   expr_id: ast::node_id, item_id: ast::node_id,
                   span: span) {

src/test/run-pass/lint-non-camel-case-with-trailing-underscores.rs

@@ -0,0 +1,6 @@
+// This is ok because we often use the trailing underscore to mean 'prime'
+
+#[forbid(non_camel_case_types)]
+type Foo_ = int;
+
+fn main() { }