syntax: Extra diagnostics for _ used in an identifier position

src/libsyntax/parse/parser.rs

@@ -574,9 +574,12 @@ impl<'a> Parser<'a> {
                 self.bug("ident interpolation not converted to real token");
             }
             _ => {
-                let token_str = self.this_token_to_string();
-                Err(self.fatal(&format!("expected ident, found `{}`",
-                                    token_str)))
+                let mut err = self.fatal(&format!("expected identifier, found `{}`",
+                                                  self.this_token_to_string()));
+                if self.token == token::Underscore {
+                    err.fileline_note(self.span, "`_` is a wildcard pattern, not an identifier");
+                }
+                Err(err)
             }
         }
     }
@@ -3782,12 +3785,6 @@ impl<'a> Parser<'a> {
     fn parse_pat_ident(&mut self,
                        binding_mode: ast::BindingMode)
                        -> PResult<'a, PatKind> {
-        if !self.token.is_plain_ident() {
-            let span = self.span;
-            let tok_str = self.this_token_to_string();
-            return Err(self.span_fatal(span,
-                            &format!("expected identifier, found `{}`", tok_str)))
-        }
         let ident = self.parse_ident()?;
         let last_span = self.last_span;
         let name = codemap::Spanned{span: last_span, node: ident};
@@ -3847,9 +3844,6 @@ impl<'a> Parser<'a> {
             Visibility::Inherited => self.span.lo,
             Visibility::Public => self.last_span.lo,
         };
-        if !self.token.is_plain_ident() {
-            return Err(self.fatal("expected ident"));
-        }
         let name = self.parse_ident()?;
         self.expect(&token::Colon)?;
         let ty = self.parse_ty_sum()?;

src/test/compile-fail/cfg-empty-codemap.rs

@@ -12,7 +12,7 @@
 
 // compile-flags: --cfg ""
 
-// error-pattern: expected ident, found
+// error-pattern: expected identifier, found
 
 pub fn main() {
 }

src/test/compile-fail/issue-20616-8.rs

@@ -40,7 +40,7 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_7 = Box<(),,>; // error: expected type, found `,`
 
 
-type Type_8<'a,,> = &'a (); //~ error: expected ident, found `,`
+type Type_8<'a,,> = &'a (); //~ error: expected identifier, found `,`
 
 
-//type Type_9<T,,> = Box<T>; // error: expected ident, found `,`
+//type Type_9<T,,> = Box<T>; // error: expected identifier, found `,`

src/test/compile-fail/issue-20616-9.rs

@@ -40,7 +40,7 @@ type Type_5_<'a> = Type_1_<'a, ()>;
 //type Type_7 = Box<(),,>; // error: expected type, found `,`
 
 
-//type Type_8<'a,,> = &'a (); // error: expected ident, found `,`
+//type Type_8<'a,,> = &'a (); // error: expected identifier, found `,`
 
 
-type Type_9<T,,> = Box<T>; //~ error: expected ident, found `,`
+type Type_9<T,,> = Box<T>; //~ error: expected identifier, found `,`

src/test/parse-fail/issue-32501.rs

@@ -0,0 +1,21 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+fn main() {
+    let a = 0;
+    let _b = 0;
+    let _ = 0;
+    let mut b = 0;
+    let mut _b = 0;
+    let mut _ = 0; //~ ERROR expected identifier, found `_`
+    //~^ NOTE `_` is a wildcard pattern, not an identifier
+}

src/test/parse-fail/paamayim-nekudotayim.rs

@@ -13,5 +13,5 @@
 // http://phpsadness.com/sad/1
 
 fn main() {
-    ::; //~ ERROR expected ident, found `;`
+    ::; //~ ERROR expected identifier, found `;`
 }

src/test/parse-fail/unboxed-closure-sugar-used-on-struct-3.rs

@@ -24,7 +24,7 @@ fn bar() {
     let b = Box::Bar::<isize,usize>::new(); // OK
 
     let b = Box::Bar::()::new();
-    //~^ ERROR expected ident, found `(`
+    //~^ ERROR expected identifier, found `(`
 }
 
 fn main() { }