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

@@ -232,15 +232,13 @@ 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

@@ -5,7 +5,7 @@ use crate::ast::{DelimArgs, Expr, ExprKind, LitKind, MetaItemLit};
 use crate::ast::{MetaItem, MetaItemKind, NestedMetaItem, NormalAttr};
 use crate::ast::{Path, PathSegment, DUMMY_NODE_ID};
 use crate::ptr::P;
-use crate::token::{self, CommentKind, Delimiter, Token};
+use crate::token::{self, CommentKind, Delimiter, InvisibleOrigin, NonterminalKind, Token};
 use crate::tokenstream::{DelimSpan, Spacing, TokenTree};
 use crate::tokenstream::{LazyAttrTokenStream, TokenStream};
 use crate::util::comments;
@@ -347,10 +347,18 @@ 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(NonterminalKind::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

@@ -825,12 +825,6 @@ fn visit_nonterminal<T: MutVisitor>(nt: &mut token::Nonterminal, vis: &mut T) {
         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 { path, args, tokens } = item.deref_mut();
-            vis.visit_path(path);
-            visit_attr_args(args, vis);
-            visit_lazy_tts(tokens, vis);
-        }
         token::NtPath(path) => vis.visit_path(path),
     }
 }

compiler/rustc_ast/src/token.rs

@@ -736,6 +736,7 @@ impl Token {
     /// That is, 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)] // njn: temp
         if let Interpolated(nt) = &self.kind
             && let NtExpr(_) | NtLiteral(_) | NtPath(_) | NtBlock(_) = &**nt
         {
@@ -921,8 +922,6 @@ 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>),
 }
 
@@ -1009,7 +1008,6 @@ impl Nonterminal {
         match self {
             NtBlock(block) => block.span,
             NtExpr(expr) | NtLiteral(expr) => expr.span,
-            NtMeta(attr_item) => attr_item.span(),
             NtPath(path) => path.span,
         }
     }
@@ -1019,7 +1017,6 @@ impl Nonterminal {
             NtBlock(..) => "block",
             NtExpr(..) => "expression",
             NtLiteral(..) => "literal",
-            NtMeta(..) => "attribute",
             NtPath(..) => "path",
         }
     }
@@ -1041,7 +1038,6 @@ 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

@@ -477,7 +477,6 @@ 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_ast_pretty/src/pprust/state.rs

@@ -854,7 +854,6 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
     fn nonterminal_to_string(&self, nt: &Nonterminal) -> String {
         match nt {
             token::NtExpr(e) => self.expr_to_string(e),
-            token::NtMeta(e) => self.attr_item_to_string(e),
             token::NtPath(e) => self.path_to_string(e),
             token::NtBlock(e) => self.block_to_string(e),
             token::NtLiteral(e) => self.expr_to_string(e),

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -306,6 +306,9 @@ pub(super) fn transcribe<'a>(
                         MatchedSingle(ParseNtResult::Ty(ref ty)) => {
                             mk_delimited(NonterminalKind::Ty, TokenStream::from_ast(ty))
                         }
+                        MatchedSingle(ParseNtResult::Meta(ref meta)) => {
+                            mk_delimited(NonterminalKind::Meta, TokenStream::from_ast(meta))
+                        }
                         MatchedSingle(ParseNtResult::Vis(ref vis)) => {
                             mk_delimited(NonterminalKind::Vis, TokenStream::from_ast(vis))
                         }

compiler/rustc_parse/messages.ftl

@@ -406,7 +406,7 @@ 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

@@ -977,7 +977,7 @@ 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

@@ -1,11 +1,11 @@
 use crate::errors;
 use crate::fluent_generated as fluent;
-use crate::maybe_whole;
+use crate::maybe_reparse_metavar_seq;
 
-use super::{AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle};
+use super::{AttrWrapper, Capturing, FnParseMode, ForceCollect, ParseNtResult, Parser, PathStyle};
 use rustc_ast as ast;
 use rustc_ast::attr;
-use rustc_ast::token::{self, Delimiter};
+use rustc_ast::token::{self, Delimiter, NonterminalKind};
 use rustc_errors::{codes::*, Diag, PResult};
 use rustc_span::{sym, BytePos, Span};
 use thin_vec::ThinVec;
@@ -249,7 +249,15 @@ 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, capture_tokens: bool) -> PResult<'a, ast::AttrItem> {
-        maybe_whole!(self, NtMeta, |attr| attr.into_inner());
+        if let Some(item) = maybe_reparse_metavar_seq!(
+            self,
+            NonterminalKind::Meta,
+            NonterminalKind::Meta,
+            ParseNtResult::Meta(item),
+            item
+        ) {
+            return Ok(item.into_inner());
+        }
 
         let do_parse = |this: &mut Self| {
             let path = this.parse_path(PathStyle::Mod)?;
@@ -360,18 +368,22 @@ impl<'a> Parser<'a> {
     /// MetaSeq = MetaItemInner (',' MetaItemInner)* ','? ;
     /// ```
     pub fn parse_meta_item(&mut self) -> 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) {
+        // Clone the parser so we can backtrack in the case where `attr_item.meta()` fails.
+        let mut parser = self.clone();
+        if let Some(attr_item) = maybe_reparse_metavar_seq!(
+            parser,
+            NonterminalKind::Meta,
+            NonterminalKind::Meta,
+            ParseNtResult::Meta(attr_item),
+            attr_item
+        ) {
+            return match attr_item.meta(attr_item.path.span) {
                 Some(meta) => {
-                    self.bump();
-                    return Ok(meta);
+                    *self = parser;
+                    Ok(meta)
                 }
-                None => self.unexpected()?,
-            }
+                None => self.unexpected_any(),
+            };
         }
 
         let lo = self.token.span;
@@ -410,7 +422,7 @@ 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,
         };