Remove NtMeta.

Note: there was an existing code path involving `Interpolated` in
`MetaItem::from_tokens` that was dead. This commit transfers that to the
new form, but puts an `unreachable!` call inside it.

Author: nnethercote

compiler/rustc_ast/src/ast_traits.rs

@@ -202,7 +202,6 @@ impl HasTokens for Nonterminal {
             Nonterminal::NtItem(item) => item.tokens(),
             Nonterminal::NtStmt(stmt) => stmt.tokens(),
             Nonterminal::NtExpr(expr) | Nonterminal::NtLiteral(expr) => expr.tokens(),
-            Nonterminal::NtMeta(attr_item) => attr_item.tokens(),
             Nonterminal::NtPath(path) => path.tokens(),
             Nonterminal::NtBlock(block) => block.tokens(),
         }
@@ -212,7 +211,6 @@ impl HasTokens for Nonterminal {
             Nonterminal::NtItem(item) => item.tokens_mut(),
             Nonterminal::NtStmt(stmt) => stmt.tokens_mut(),
             Nonterminal::NtExpr(expr) | Nonterminal::NtLiteral(expr) => expr.tokens_mut(),
-            Nonterminal::NtMeta(attr_item) => attr_item.tokens_mut(),
             Nonterminal::NtPath(path) => path.tokens_mut(),
             Nonterminal::NtBlock(block) => block.tokens_mut(),
         }

compiler/rustc_ast/src/attr/mod.rs

@@ -14,7 +14,7 @@ use crate::ast::{
     PathSegment, Safety,
 };
 use crate::ptr::P;
-use crate::token::{self, CommentKind, Delimiter, Token};
+use crate::token::{self, CommentKind, Delimiter, InvisibleOrigin, MetaVarKind, Token};
 use crate::tokenstream::{
     DelimSpan, LazyAttrTokenStream, Spacing, TokenStream, TokenStreamIter, TokenTree,
 };
@@ -406,10 +406,18 @@ impl MetaItem {
                 Path { span, segments, tokens: None }
             }
             Some(TokenTree::Token(Token { kind: token::Interpolated(nt), .. }, _)) => match &**nt {
-                token::Nonterminal::NtMeta(item) => return item.meta(item.path.span),
                 token::Nonterminal::NtPath(path) => (**path).clone(),
                 _ => return None,
             },
+            Some(TokenTree::Delimited(
+                _span,
+                _spacing,
+                Delimiter::Invisible(InvisibleOrigin::MetaVar(MetaVarKind::Meta { .. })),
+                _stream,
+            )) => {
+                // This path is currently unreachable in the test suite.
+                unreachable!()
+            }
             Some(TokenTree::Token(
                 Token { kind: token::OpenDelim(_) | token::CloseDelim(_), .. },
                 _,

compiler/rustc_ast/src/mut_visit.rs

@@ -907,12 +907,6 @@ fn visit_nonterminal<T: MutVisitor>(vis: &mut T, nt: &mut token::Nonterminal) {
         }),
         token::NtExpr(expr) => vis.visit_expr(expr),
         token::NtLiteral(expr) => vis.visit_expr(expr),
-        token::NtMeta(item) => {
-            let AttrItem { unsafety: _, path, args, tokens } = item.deref_mut();
-            vis.visit_path(path);
-            visit_attr_args(vis, args);
-            visit_lazy_tts(vis, tokens);
-        }
         token::NtPath(path) => vis.visit_path(path),
     }
 }

compiler/rustc_ast/src/token.rs

@@ -90,7 +90,10 @@ pub enum MetaVarKind {
     Ident,
     Lifetime,
     Literal,
-    Meta,
+    Meta {
+        /// Will `AttrItem::meta` succeed on this, if reparsed?
+        has_meta_form: bool,
+    },
     Path,
     Vis,
     TT,
@@ -110,7 +113,7 @@ impl fmt::Display for MetaVarKind {
             MetaVarKind::Ident => sym::ident,
             MetaVarKind::Lifetime => sym::lifetime,
             MetaVarKind::Literal => sym::literal,
-            MetaVarKind::Meta => sym::meta,
+            MetaVarKind::Meta { .. } => sym::meta,
             MetaVarKind::Path => sym::path,
             MetaVarKind::Vis => sym::vis,
             MetaVarKind::TT => sym::tt,
@@ -658,13 +661,12 @@ impl Token {
                 matches!(&**nt,
                     | NtExpr(..)
                     | NtLiteral(..)
-                    | NtMeta(..)
                     | NtPath(..)
                 ),
             OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(
                 MetaVarKind::Expr { .. } |
                 MetaVarKind::Literal |
-                MetaVarKind::Meta |
+                MetaVarKind::Meta { .. } |
                 MetaVarKind::Pat(_) |
                 MetaVarKind::Path |
                 MetaVarKind::Ty { .. }
@@ -1076,8 +1078,6 @@ pub enum Nonterminal {
     NtStmt(P<ast::Stmt>),
     NtExpr(P<ast::Expr>),
     NtLiteral(P<ast::Expr>),
-    /// Stuff inside brackets for attributes
-    NtMeta(P<ast::AttrItem>),
     NtPath(P<ast::Path>),
 }
 
@@ -1171,7 +1171,6 @@ impl Nonterminal {
             NtBlock(block) => block.span,
             NtStmt(stmt) => stmt.span,
             NtExpr(expr) | NtLiteral(expr) => expr.span,
-            NtMeta(attr_item) => attr_item.span(),
             NtPath(path) => path.span,
         }
     }
@@ -1183,7 +1182,6 @@ impl Nonterminal {
             NtStmt(..) => "statement",
             NtExpr(..) => "expression",
             NtLiteral(..) => "literal",
-            NtMeta(..) => "attribute",
             NtPath(..) => "path",
         }
     }
@@ -1207,7 +1205,6 @@ impl fmt::Debug for Nonterminal {
             NtStmt(..) => f.pad("NtStmt(..)"),
             NtExpr(..) => f.pad("NtExpr(..)"),
             NtLiteral(..) => f.pad("NtLiteral(..)"),
-            NtMeta(..) => f.pad("NtMeta(..)"),
             NtPath(..) => f.pad("NtPath(..)"),
         }
     }

compiler/rustc_ast/src/tokenstream.rs

@@ -468,7 +468,6 @@ impl TokenStream {
                 TokenStream::token_alone(token::Semi, stmt.span)
             }
             Nonterminal::NtStmt(stmt) => TokenStream::from_ast(stmt),
-            Nonterminal::NtMeta(attr) => TokenStream::from_ast(attr),
             Nonterminal::NtPath(path) => TokenStream::from_ast(path),
             Nonterminal::NtExpr(expr) | Nonterminal::NtLiteral(expr) => TokenStream::from_ast(expr),
         }

compiler/rustc_attr_parsing/src/parser.rs

@@ -481,15 +481,6 @@ impl<'a> MetaItemListParserContext<'a> {
                 self.inside_delimiters.peek()
             {
                 match &**nt {
-                    // or maybe a full nt meta including the path but we return immediately
-                    token::Nonterminal::NtMeta(item) => {
-                        self.inside_delimiters.next();
-
-                        return Some(MetaItemOrLitParser::MetaItemParser(MetaItemParser {
-                            path: PathParser::Ast(&item.path),
-                            args: ArgParser::from_attr_args(&item.args, self.dcx),
-                        }));
-                    }
                     // an already interpolated path from a macro expansion is a path, no need to parse
                     // one from tokens
                     token::Nonterminal::NtPath(path) => {

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -336,6 +336,14 @@ pub(super) fn transcribe<'a>(
                                 TokenStream::from_ast(ty),
                             )
                         }
+                        MatchedSingle(ParseNtResult::Meta(attr_item)) => {
+                            let has_meta_form = attr_item.meta_kind().is_some();
+                            mk_delimited(
+                                attr_item.span(),
+                                MetaVarKind::Meta { has_meta_form },
+                                TokenStream::from_ast(attr_item),
+                            )
+                        }
                         MatchedSingle(ParseNtResult::Vis(vis)) => {
                             mk_delimited(vis.span, MetaVarKind::Vis, TokenStream::from_ast(vis))
                         }

compiler/rustc_parse/messages.ftl

@@ -424,7 +424,7 @@ parse_invalid_logical_operator = `{$incorrect}` is not a logical operator
     .use_amp_amp_for_conjunction = use `&&` to perform logical conjunction
     .use_pipe_pipe_for_disjunction = use `||` to perform logical disjunction
 
-parse_invalid_meta_item = expected unsuffixed literal, found `{$token}`
+parse_invalid_meta_item = expected unsuffixed literal, found {$descr}
     .quote_ident_sugg = surround the identifier with quotation marks to make it into a string literal
 
 parse_invalid_offset_of = offset_of expects dot-separated field and variant names

compiler/rustc_parse/src/errors.rs

@@ -1024,7 +1024,7 @@ pub(crate) struct SuffixedLiteralInAttribute {
 pub(crate) struct InvalidMetaItem {
     #[primary_span]
     pub span: Span,
-    pub token: Token,
+    pub descr: String,
     #[subdiagnostic]
     pub quote_ident_sugg: Option<InvalidMetaItemQuoteIdentSugg>,
 }

compiler/rustc_parse/src/parser/attr.rs

@@ -1,4 +1,6 @@
-use rustc_ast::{self as ast, Attribute, attr, token};
+use rustc_ast as ast;
+use rustc_ast::token::{self, MetaVarKind};
+use rustc_ast::{Attribute, attr};
 use rustc_errors::codes::*;
 use rustc_errors::{Diag, PResult};
 use rustc_span::{BytePos, Span};
@@ -9,7 +11,7 @@ use super::{
     AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, ParserRange, PathStyle, Trailing,
     UsePreAttrPos,
 };
-use crate::{errors, exp, fluent_generated as fluent, maybe_whole};
+use crate::{errors, exp, fluent_generated as fluent};
 
 // Public for rustfmt usage
 #[derive(Debug)]
@@ -269,7 +271,12 @@ impl<'a> Parser<'a> {
     ///     PATH `=` UNSUFFIXED_LIT
     /// The delimiters or `=` are still put into the resulting token stream.
     pub fn parse_attr_item(&mut self, force_collect: ForceCollect) -> PResult<'a, ast::AttrItem> {
-        maybe_whole!(self, NtMeta, |attr| attr.into_inner());
+        if let Some(item) = self.eat_metavar_seq_with_matcher(
+            |mv_kind| matches!(mv_kind, MetaVarKind::Meta { .. }),
+            |this| this.parse_attr_item(force_collect),
+        ) {
+            return Ok(item);
+        }
 
         // Attr items don't have attributes.
         self.collect_tokens(None, AttrWrapper::empty(), force_collect, |this, _empty_attrs| {
@@ -396,18 +403,17 @@ impl<'a> Parser<'a> {
         &mut self,
         unsafe_allowed: AllowLeadingUnsafe,
     ) -> PResult<'a, ast::MetaItem> {
-        // We can't use `maybe_whole` here because it would bump in the `None`
-        // case, which we don't want.
-        if let token::Interpolated(nt) = &self.token.kind
-            && let token::NtMeta(attr_item) = &**nt
-        {
-            match attr_item.meta(attr_item.path.span) {
-                Some(meta) => {
-                    self.bump();
-                    return Ok(meta);
-                }
-                None => self.unexpected()?,
-            }
+        if let Some(MetaVarKind::Meta { has_meta_form }) = self.token.is_metavar_seq() {
+            return if has_meta_form {
+                let attr_item = self
+                    .eat_metavar_seq(MetaVarKind::Meta { has_meta_form: true }, |this| {
+                        this.parse_attr_item(ForceCollect::No)
+                    })
+                    .unwrap();
+                Ok(attr_item.meta(attr_item.path.span).unwrap())
+            } else {
+                self.unexpected_any()
+            };
         }
 
         let lo = self.token.span;
@@ -464,7 +470,7 @@ impl<'a> Parser<'a> {
 
         let mut err = errors::InvalidMetaItem {
             span: self.token.span,
-            token: self.token.clone(),
+            descr: super::token_descr(&self.token),
             quote_ident_sugg: None,
         };