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

@@ -200,15 +200,13 @@ impl HasTokens for Nonterminal {
     fn tokens(&self) -> Option<&LazyAttrTokenStream> {
         match self {
             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(),
         }
     }
     fn tokens_mut(&mut self) -> Option<&mut Option<LazyAttrTokenStream>> {
         match self {
             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

@@ -15,7 +15,7 @@ use crate::ast::{
     NormalAttr, Path, 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, TokenTree};
 use crate::util::comments;
 use crate::util::literal::escape_string_symbol;
@@ -365,10 +365,18 @@ 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

@@ -803,12 +803,6 @@ fn visit_nonterminal<T: MutVisitor>(vis: &mut T, nt: &mut token::Nonterminal) {
         token::NtBlock(block) => vis.visit_block(block),
         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

@@ -657,7 +657,6 @@ impl Token {
                 matches!(&**nt,
                     | NtExpr(..)
                     | NtLiteral(..)
-                    | NtMeta(..)
                     | NtPath(..)
                 ),
             OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(
@@ -860,6 +859,7 @@ impl Token {
     /// Is this a pre-parsed expression dropped into the token stream
     /// (which happens while parsing the result of macro expansion)?
     pub fn is_whole_expr(&self) -> bool {
+        #[allow(irrefutable_let_patterns)] // FIXME: temporary
         if let Interpolated(nt) = &self.kind
             && let NtExpr(_) | NtLiteral(_) | NtPath(_) | NtBlock(_) = &**nt
         {
@@ -1066,8 +1066,6 @@ pub enum Nonterminal {
     NtBlock(P<ast::Block>),
     NtExpr(P<ast::Expr>),
     NtLiteral(P<ast::Expr>),
-    /// Stuff inside brackets for attributes
-    NtMeta(P<ast::AttrItem>),
     NtPath(P<ast::Path>),
 }
 
@@ -1159,7 +1157,6 @@ impl Nonterminal {
         match self {
             NtBlock(block) => block.span,
             NtExpr(expr) | NtLiteral(expr) => expr.span,
-            NtMeta(attr_item) => attr_item.span(),
             NtPath(path) => path.span,
         }
     }
@@ -1169,7 +1166,6 @@ impl Nonterminal {
             NtBlock(..) => "block",
             NtExpr(..) => "expression",
             NtLiteral(..) => "literal",
-            NtMeta(..) => "attribute",
             NtPath(..) => "path",
         }
     }
@@ -1191,7 +1187,6 @@ impl fmt::Debug for Nonterminal {
             NtBlock(..) => f.pad("NtBlock(..)"),
             NtExpr(..) => f.pad("NtExpr(..)"),
             NtLiteral(..) => f.pad("NtLiteral(..)"),
-            NtMeta(..) => f.pad("NtMeta(..)"),
             NtPath(..) => f.pad("NtPath(..)"),
         }
     }

compiler/rustc_ast/src/tokenstream.rs

@@ -462,7 +462,6 @@ impl TokenStream {
     pub fn from_nonterminal_ast(nt: &Nonterminal) -> TokenStream {
         match nt {
             Nonterminal::NtBlock(block) => TokenStream::from_ast(block),
-            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_expand/src/mbe/transcribe.rs

@@ -335,6 +335,9 @@ pub(super) fn transcribe<'a>(
                         MatchedSingle(ParseNtResult::Ty(ty)) => {
                             mk_delimited(MetaVarKind::Ty, TokenStream::from_ast(ty))
                         }
+                        MatchedSingle(ParseNtResult::Meta(meta)) => {
+                            mk_delimited(MetaVarKind::Meta, TokenStream::from_ast(meta))
+                        }
                         MatchedSingle(ParseNtResult::Vis(vis)) => {
                             mk_delimited(MetaVarKind::Vis, TokenStream::from_ast(vis))
                         }

compiler/rustc_parse/messages.ftl

@@ -415,7 +415,7 @@ 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

@@ -1,6 +1,6 @@
 use rustc_ast as ast;
 use rustc_ast::attr;
-use rustc_ast::token::{self, Delimiter};
+use rustc_ast::token::{self, Delimiter, MetaVarKind};
 use rustc_errors::codes::*;
 use rustc_errors::{Diag, PResult};
 use rustc_span::symbol::kw;
@@ -12,7 +12,7 @@ use super::{
     AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, ParserRange, PathStyle, Trailing,
     UsePreAttrPos,
 };
-use crate::{errors, fluent_generated as fluent, maybe_whole};
+use crate::{errors, fluent_generated as fluent};
 
 // Public for rustfmt usage
 #[derive(Debug)]
@@ -272,7 +272,11 @@ 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(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| {
@@ -397,18 +401,18 @@ 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
+        // Snapshot the parser so we can backtrack in the case where `attr_item.meta()` fails.
+        let mut snapshot = self.create_snapshot_for_diagnostic();
+        if let Some(attr_item) = snapshot
+            .eat_metavar_seq(MetaVarKind::Meta, |this| this.parse_attr_item(ForceCollect::No))
         {
-            match attr_item.meta(attr_item.path.span) {
+            return match attr_item.meta(attr_item.path.span) {
                 Some(meta) => {
-                    self.bump();
-                    return Ok(meta);
+                    self.restore_snapshot(snapshot);
+                    Ok(meta)
                 }
-                None => self.unexpected()?,
-            }
+                None => self.unexpected_any(),
+            };
         }
 
         let lo = self.token.span;
@@ -465,7 +469,7 @@ 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,
         };
 

compiler/rustc_parse/src/parser/expr.rs

@@ -1399,7 +1399,6 @@ impl<'a> Parser<'a> {
                     self.bump();
                     return Ok(self.mk_expr(self.prev_token.span, ExprKind::Block(block, None)));
                 }
-                _ => {}
             };
         }