Tweak chained comparison errors.

Lower case and give a more precise span: from operator to operator, not
just the last one.

Author: huonw

src/libsyntax/parse/parser.rs

@@ -2882,12 +2882,13 @@ impl<'a> Parser<'a> {
         debug_assert!(ast_util::is_comparison_binop(outer_op));
         match lhs.node {
             ExprBinary(op, _, _) if ast_util::is_comparison_binop(op.node) => {
-                let op_span = self.span;
+                // respan to include both operators
+                let op_span = mk_sp(op.span.lo, self.span.hi);
                 self.span_err(op_span,
-                    "Chained comparison operators require parentheses");
+                    "chained comparison operators require parentheses");
                 if op.node == BiLt && outer_op == BiGt {
                     self.span_help(op_span,
-                        "use ::< instead of < if you meant to specify type arguments");
+                        "use `::<...>` instead of `<...>` if you meant to specify type arguments");
                 }
             }
             _ => {}

src/test/compile-fail/require-parens-for-chained-comparison.rs

@@ -12,12 +12,12 @@ fn f<T>() {}
 
 fn main() {
     false == false == false;
-    //~^ ERROR: Chained comparison operators require parentheses
+    //~^ ERROR: chained comparison operators require parentheses
 
     false == 0 < 2;
-    //~^ ERROR: Chained comparison operators require parentheses
+    //~^ ERROR: chained comparison operators require parentheses
 
     f<X>();
-    //~^ ERROR: Chained comparison operators require parentheses
-    //~^^ HELP: use ::< instead of < if you meant to specify type arguments
+    //~^ ERROR: chained comparison operators require parentheses
+    //~^^ HELP: use `::<...>` instead of `<...>`
 }

src/test/compile-fail/unsized2.rs

@@ -15,6 +15,6 @@ fn f<X>() {}
 pub fn main() {
     f<type>();
     //~^ ERROR expected identifier, found keyword `type`
-    //~^^ ERROR: Chained comparison operators require parentheses
-    //~^^^ HELP: use ::< instead of < if you meant to specify type arguments
+    //~^^ ERROR: chained comparison
+    //~^^^ HELP: use `::<
 }