Tweak expand_incomplete_parse warning.

By using `token_descr`, as is done for many other errors, we can get
slightly better descriptions in error messages, e.g.
"macro expansion ignores token `let` and any following" becomes
"macro expansion ignores keyword `let` and any tokens following".

This will be more important once invisible delimiters start being
mentioned in error messages -- without this commit, that leads to error
messages such as "error at ``" because invisible delimiters are
pretty printed as an empty string.

Author: nnethercote

compiler/rustc_expand/messages.ftl

@@ -74,7 +74,7 @@ expand_helper_attribute_name_invalid =
     `{$name}` cannot be a name of derive helper attribute
 
 expand_incomplete_parse =
-    macro expansion ignores token `{$token}` and any following
+    macro expansion ignores {$descr} and any tokens following
     .label = caused by the macro expansion here
     .note = the usage of `{$macro_path}!` is likely invalid in {$kind_name} context
     .suggestion_add_semi = you might be missing a semicolon here

compiler/rustc_expand/src/errors.rs

@@ -275,7 +275,7 @@ pub(crate) struct UnsupportedKeyValue {
 pub(crate) struct IncompleteParse<'a> {
     #[primary_span]
     pub span: Span,
-    pub token: Cow<'a, str>,
+    pub descr: String,
     #[label]
     pub label_span: Span,
     pub macro_path: &'a ast::Path,

compiler/rustc_expand/src/expand.rs

@@ -21,6 +21,7 @@ use rustc_errors::PResult;
 use rustc_feature::Features;
 use rustc_parse::parser::{
     AttemptLocalParseRecovery, CommaRecoveryMode, ForceCollect, Parser, RecoverColon, RecoverComma,
+    token_descr,
 };
 use rustc_parse::validate_attr;
 use rustc_session::lint::BuiltinLintDiag;
@@ -1013,7 +1014,7 @@ pub(crate) fn ensure_complete_parse<'a>(
     span: Span,
 ) {
     if parser.token != token::Eof {
-        let token = pprust::token_to_string(&parser.token);
+        let descr = token_descr(&parser.token);
         // Avoid emitting backtrace info twice.
         let def_site_span = parser.token.span.with_ctxt(SyntaxContext::root());
 
@@ -1029,7 +1030,7 @@ pub(crate) fn ensure_complete_parse<'a>(
 
         parser.dcx().emit_err(IncompleteParse {
             span: def_site_span,
-            token,
+            descr,
             label_span: span,
             macro_path,
             kind_name,

compiler/rustc_parse/src/parser/mod.rs

@@ -424,7 +424,7 @@ impl TokenDescription {
     }
 }
 
-pub(super) fn token_descr(token: &Token) -> String {
+pub fn token_descr(token: &Token) -> String {
     let name = pprust::token_to_string(token).to_string();
 
     let kind = match (TokenDescription::from_token(token), &token.kind) {

tests/ui/macros/issue-118786.rs

@@ -5,7 +5,7 @@
 macro_rules! make_macro {
     ($macro_name:tt) => {
         macro_rules! $macro_name {
-        //~^ ERROR macro expansion ignores token `{` and any following
+        //~^ ERROR macro expansion ignores `{` and any tokens following
         //~| ERROR cannot find macro `macro_rules` in this scope
         //~| put a macro name here
             () => {}

tests/ui/macros/issue-118786.stderr

@@ -13,7 +13,7 @@ help: add a semicolon
 LL |         macro_rules! $macro_name; {
    |                                 +
 
-error: macro expansion ignores token `{` and any following
+error: macro expansion ignores `{` and any tokens following
   --> $DIR/issue-118786.rs:7:34
    |
 LL |         macro_rules! $macro_name {

tests/ui/macros/issue-30007.rs

@@ -1,5 +1,5 @@
 macro_rules! t {
-    () => ( String ; );     //~ ERROR macro expansion ignores token `;`
+    () => ( String ; );     //~ ERROR macro expansion ignores `;`
 }
 
 fn main() {

tests/ui/macros/issue-30007.stderr

@@ -1,4 +1,4 @@
-error: macro expansion ignores token `;` and any following
+error: macro expansion ignores `;` and any tokens following
   --> $DIR/issue-30007.rs:2:20
    |
 LL |     () => ( String ; );

tests/ui/macros/issue-54441.rs

@@ -1,6 +1,6 @@
 macro_rules! m {
     () => {
-        let //~ ERROR macro expansion ignores token `let` and any following
+        let //~ ERROR macro expansion ignores keyword `let` and any tokens following
     };
 }
 

tests/ui/macros/issue-54441.stderr

@@ -1,4 +1,4 @@
-error: macro expansion ignores token `let` and any following
+error: macro expansion ignores keyword `let` and any tokens following
   --> $DIR/issue-54441.rs:3:9
    |
 LL |         let