Do not propose suggestions for idents without case

src/librustc/lint/builtin.rs

@@ -938,10 +938,9 @@ pub struct NonSnakeCase;
 
 impl NonSnakeCase {
     fn check_snake_case(&self, cx: &Context, sort: &str, ident: ast::Ident, span: Span) {
-        fn is_snake_case(ident: ast::Ident) -> bool {
-            let ident = token::get_ident(ident);
-            if ident.get().is_empty() { return true; }
-            let ident = ident.get().trim_left_matches('\'');
+        fn is_snake_case(ident: &str) -> bool {
+            if ident.is_empty() { return true; }
+            let ident = ident.trim_left_matches('\'');
             let ident = ident.trim_matches('_');
 
             let mut allow_underscore = true;
@@ -978,10 +977,16 @@ impl NonSnakeCase {
 
         let s = token::get_ident(ident);
 
-        if !is_snake_case(ident) {
-            cx.span_lint(NON_SNAKE_CASE, span,
-                &format!("{} `{}` should have a snake case name such as `{}`",
-                        sort, s, to_snake_case(s.get()))[]);
+        if !is_snake_case(s.get()) {
+            let snaked = to_snake_case(s.get());
+            if is_snake_case(&*snaked) {
+                cx.span_lint(NON_SNAKE_CASE, span,
+                             &format!("{} `{}` should have a snake case name such as `{}`",
+                                      sort, s, snaked)[]);
+            } else {
+                cx.span_lint(NON_SNAKE_CASE, span,
+                             &format!("{} `{}` should have a snake case name", sort, s)[]);
+            }
         }
     }
 }

src/test/compile-fail/lint-non-snake-case-functions.rs

@@ -10,6 +10,7 @@
 
 #![deny(non_snake_case)]
 #![allow(dead_code)]
+#![feature(non_ascii_idents)]
 
 struct Foo;
 
@@ -26,6 +27,9 @@ impl Foo {
 
     fn render_HTML() {}
     //~^ ERROR method `render_HTML` should have a snake case name such as `render_html`
+
+    fn を() {}
+    //~^ ERROR method `を` should have a snake case name
 }
 
 trait X {
@@ -37,6 +41,9 @@ trait X {
 
     fn something__else(&mut self);
     //~^ ERROR trait method `something__else` should have a snake case name such as `something_else`
+
+    fn あ() {}
+    //~^ ERROR method `あ` should have a snake case name
 }
 
 impl X for Foo {
@@ -51,4 +58,7 @@ fn Cookie() {}
 pub fn bi_S_Cuit() {}
 //~^ ERROR function `bi_S_Cuit` should have a snake case name such as `bi_s_cuit`
 
+pub fn お() {}
+//~^ ERROR function `お` should have a snake case name
+
 fn main() { }