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.

Author: nnethercote

compiler/rustc_expand/messages.ftl

@@ -50,7 +50,7 @@ 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

@@ -4,7 +4,6 @@ use rustc_session::Limit;
 use rustc_span::edition::Edition;
 use rustc_span::symbol::{Ident, MacroRulesNormalizedIdent};
 use rustc_span::{Span, Symbol};
-use std::borrow::Cow;
 
 #[derive(Diagnostic)]
 #[diag(expand_expr_repeat_no_syntax_vars)]
@@ -299,7 +298,7 @@ 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

@@ -25,7 +25,8 @@ use rustc_data_structures::sync::Lrc;
 use rustc_errors::PResult;
 use rustc_feature::Features;
 use rustc_parse::parser::{
-    AttemptLocalParseRecovery, CommaRecoveryMode, ForceCollect, Parser, RecoverColon, RecoverComma,
+    token_descr, AttemptLocalParseRecovery, CommaRecoveryMode, ForceCollect, Parser, RecoverColon,
+    RecoverComma,
 };
 use rustc_parse::validate_attr;
 use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
@@ -943,7 +944,7 @@ pub 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());
 
@@ -957,7 +958,7 @@ pub fn ensure_complete_parse<'a>(
 
         parser.sess.emit_err(IncompleteParse {
             span: def_site_span,
-            token,
+            descr,
             label_span: span,
             macro_path,
             kind_name,

compiler/rustc_parse/src/parser/mod.rs

@@ -370,7 +370,10 @@ impl TokenDescription {
     }
 }
 
-pub(super) fn token_descr(token: &Token) -> String {
+/// Provide a description of a token for error messages. In most cases the
+/// result is the same as pretty-printing it, but for a few token kinds we can
+/// do better.
+pub fn token_descr(token: &Token) -> String {
     use TokenDescription::*;
 
     let s = pprust::token_to_string(token).to_string();

tests/ui/issues/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/issues/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

tests/ui/macros/macro-context.rs

@@ -1,9 +1,9 @@
 // (typeof used because it's surprisingly hard to find an unparsed token after a stmt)
 macro_rules! m {
     () => ( i ; typeof );   //~ ERROR expected expression, found reserved keyword `typeof`
-                            //~| ERROR macro expansion ignores token `typeof`
-                            //~| ERROR macro expansion ignores token `;`
-                            //~| ERROR macro expansion ignores token `;`
+                            //~| ERROR macro expansion ignores reserved keyword `typeof`
+                            //~| ERROR macro expansion ignores `;`
+                            //~| ERROR macro expansion ignores `;`
                             //~| ERROR cannot find type `i` in this scope
                             //~| ERROR cannot find value `i` in this scope
                             //~| WARN trailing semicolon in macro

tests/ui/macros/macro-context.stderr

@@ -1,4 +1,4 @@
-error: macro expansion ignores token `;` and any following
+error: macro expansion ignores `;` and any tokens following
   --> $DIR/macro-context.rs:3:15
    |
 LL |     () => ( i ; typeof );
@@ -9,7 +9,7 @@ LL |     let a: m!();
    |
    = note: the usage of `m!` is likely invalid in type context
 
-error: macro expansion ignores token `typeof` and any following
+error: macro expansion ignores reserved keyword `typeof` and any tokens following
   --> $DIR/macro-context.rs:3:17
    |
 LL |     () => ( i ; typeof );
@@ -20,7 +20,7 @@ LL |     let i = m!();
    |
    = note: the usage of `m!` is likely invalid in expression context
 
-error: macro expansion ignores token `;` and any following
+error: macro expansion ignores `;` and any tokens following
   --> $DIR/macro-context.rs:3:15
    |
 LL |     () => ( i ; typeof );