mbe: Refine error message for attribute argument delimiters

Author: joshtriplett

compiler/rustc_expand/messages.ftl

@@ -70,7 +70,7 @@ expand_invalid_fragment_specifier =
     invalid fragment specifier `{$fragment}`
     .help = {$help}
 
-expand_macro_args_bad_delim = macro argument matchers require parentheses
+expand_macro_args_bad_delim = macro attribute argument matchers require parentheses
 expand_macro_args_bad_delim_sugg = the delimiters should be `(` and `)`
 
 expand_macro_body_stability =

tests/ui/parser/macro/macro-attr-bad.rs

@@ -14,10 +14,10 @@ macro_rules! attr_incomplete_4 { attr() {} => }
 //~^ ERROR macro definition ended unexpectedly
 
 macro_rules! attr_noparens_1 { attr{} {} => {} }
-//~^ ERROR macro argument matchers require parentheses
+//~^ ERROR macro attribute argument matchers require parentheses
 
 macro_rules! attr_noparens_2 { attr[] {} => {} }
-//~^ ERROR macro argument matchers require parentheses
+//~^ ERROR macro attribute argument matchers require parentheses
 
 macro_rules! attr_noparens_3 { attr _ {} => {} }
 //~^ ERROR invalid macro matcher

tests/ui/parser/macro/macro-attr-bad.stderr

@@ -22,7 +22,7 @@ error: macro definition ended unexpectedly
 LL | macro_rules! attr_incomplete_4 { attr() {} => }
    |                                              ^ expected right-hand side of macro rule
 
-error: macro argument matchers require parentheses
+error: macro attribute argument matchers require parentheses
   --> $DIR/macro-attr-bad.rs:16:36
    |
 LL | macro_rules! attr_noparens_1 { attr{} {} => {} }
@@ -34,7 +34,7 @@ LL - macro_rules! attr_noparens_1 { attr{} {} => {} }
 LL + macro_rules! attr_noparens_1 { attr() {} => {} }
    |
 
-error: macro argument matchers require parentheses
+error: macro attribute argument matchers require parentheses
   --> $DIR/macro-attr-bad.rs:19:36
    |
 LL | macro_rules! attr_noparens_2 { attr[] {} => {} }