Remove NtVis.

We now use invisible delimiters for expanded `vis` fragments, instead of
`Token::Interpolated`.

Author: nnethercote

compiler/rustc_ast/src/ast_traits.rs

@@ -206,7 +206,6 @@ impl HasTokens for Nonterminal {
             Nonterminal::NtTy(ty) => ty.tokens(),
             Nonterminal::NtMeta(attr_item) => attr_item.tokens(),
             Nonterminal::NtPath(path) => path.tokens(),
-            Nonterminal::NtVis(vis) => vis.tokens(),
             Nonterminal::NtBlock(block) => block.tokens(),
         }
     }
@@ -219,7 +218,6 @@ impl HasTokens for Nonterminal {
             Nonterminal::NtTy(ty) => ty.tokens_mut(),
             Nonterminal::NtMeta(attr_item) => attr_item.tokens_mut(),
             Nonterminal::NtPath(path) => path.tokens_mut(),
-            Nonterminal::NtVis(vis) => vis.tokens_mut(),
             Nonterminal::NtBlock(block) => block.tokens_mut(),
         }
     }

compiler/rustc_ast/src/mut_visit.rs

@@ -824,7 +824,6 @@ fn visit_nonterminal<T: MutVisitor>(vis: &mut T, nt: &mut token::Nonterminal) {
             visit_lazy_tts(vis, tokens);
         }
         token::NtPath(path) => vis.visit_path(path),
-        token::NtVis(visib) => vis.visit_vis(visib),
     }
 }
 

compiler/rustc_ast/src/token.rs

@@ -963,6 +963,15 @@ impl Token {
         }
     }
 
+    /// Is this an invisible open delimiter at the start of a token sequence
+    /// from an expanded metavar?
+    pub fn is_metavar_seq(&self) -> Option<MetaVarKind> {
+        match self.kind {
+            OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(kind))) => Some(kind),
+            _ => None,
+        }
+    }
+
     pub fn glue(&self, joint: &Token) -> Option<Token> {
         let kind = match self.kind {
             Eq => match joint.kind {
@@ -1066,7 +1075,6 @@ pub enum Nonterminal {
     /// Stuff inside brackets for attributes
     NtMeta(P<ast::AttrItem>),
     NtPath(P<ast::Path>),
-    NtVis(P<ast::Visibility>),
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Encodable, Decodable, Hash, HashStable_Generic)]
@@ -1163,7 +1171,6 @@ impl Nonterminal {
             NtTy(ty) => ty.span,
             NtMeta(attr_item) => attr_item.span(),
             NtPath(path) => path.span,
-            NtVis(vis) => vis.span,
         }
     }
 
@@ -1178,7 +1185,6 @@ impl Nonterminal {
             NtTy(..) => "type",
             NtMeta(..) => "attribute",
             NtPath(..) => "path",
-            NtVis(..) => "visibility",
         }
     }
 }
@@ -1205,7 +1211,6 @@ impl fmt::Debug for Nonterminal {
             NtLiteral(..) => f.pad("NtLiteral(..)"),
             NtMeta(..) => f.pad("NtMeta(..)"),
             NtPath(..) => f.pad("NtPath(..)"),
-            NtVis(..) => f.pad("NtVis(..)"),
         }
     }
 }

compiler/rustc_ast/src/tokenstream.rs

@@ -472,7 +472,6 @@ impl TokenStream {
             Nonterminal::NtTy(ty) => TokenStream::from_ast(ty),
             Nonterminal::NtMeta(attr) => TokenStream::from_ast(attr),
             Nonterminal::NtPath(path) => TokenStream::from_ast(path),
-            Nonterminal::NtVis(vis) => TokenStream::from_ast(vis),
             Nonterminal::NtExpr(expr) | Nonterminal::NtLiteral(expr) => TokenStream::from_ast(expr),
         }
     }

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -2,7 +2,10 @@ use std::mem;
 
 use rustc_ast::ExprKind;
 use rustc_ast::mut_visit::{self, MutVisitor};
-use rustc_ast::token::{self, Delimiter, IdentIsRaw, Lit, LitKind, Nonterminal, Token, TokenKind};
+use rustc_ast::token::{
+    self, Delimiter, IdentIsRaw, InvisibleOrigin, Lit, LitKind, MetaVarKind, Nonterminal, Token,
+    TokenKind,
+};
 use rustc_ast::tokenstream::{DelimSpacing, DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{Diag, DiagCtxtHandle, PResult, pluralize};
@@ -252,7 +255,6 @@ pub(super) fn transcribe<'a>(
                 }
             }
 
-            // Replace the meta-var with the matched token tree from the invocation.
             mbe::TokenTree::MetaVar(mut sp, mut original_ident) => {
                 // Find the matched nonterminal from the macro invocation, and use it to replace
                 // the meta-var.
@@ -272,6 +274,33 @@ pub(super) fn transcribe<'a>(
                 // some of the unnecessary whitespace.
                 let ident = MacroRulesNormalizedIdent::new(original_ident);
                 if let Some(cur_matched) = lookup_cur_matched(ident, interp, &repeats) {
+                    // We wrap the tokens in invisible delimiters, unless they are already wrapped
+                    // in invisible delimiters with the same `MetaVarKind`. Because there is no
+                    // point in having multiple layers of invisible delimiters of the same
+                    // `MetaVarKind`. Indeed, some proc macros can't handle them.
+                    let mut mk_delimited = |mv_kind, mut stream: TokenStream| {
+                        if stream.len() == 1 {
+                            let tree = stream.trees().next().unwrap();
+                            if let TokenTree::Delimited(_, _, delim, inner) = tree
+                                && let Delimiter::Invisible(InvisibleOrigin::MetaVar(mvk)) = delim
+                                && mv_kind == *mvk
+                            {
+                                stream = inner.clone();
+                            }
+                        }
+
+                        // Emit as a token stream within `Delimiter::Invisible` to maintain
+                        // parsing priorities.
+                        marker.visit_span(&mut sp);
+                        // Both the open delim and close delim get the same span, which covers the
+                        // `$foo` in the decl macro RHS.
+                        TokenTree::Delimited(
+                            DelimSpan::from_single(sp),
+                            DelimSpacing::new(Spacing::Alone, Spacing::Alone),
+                            Delimiter::Invisible(InvisibleOrigin::MetaVar(mv_kind)),
+                            stream,
+                        )
+                    };
                     let tt = match cur_matched {
                         MatchedSingle(ParseNtResult::Tt(tt)) => {
                             // `tt`s are emitted into the output stream directly as "raw tokens",
@@ -288,6 +317,9 @@ pub(super) fn transcribe<'a>(
                             let kind = token::NtLifetime(*ident, *is_raw);
                             TokenTree::token_alone(kind, sp)
                         }
+                        MatchedSingle(ParseNtResult::Vis(vis)) => {
+                            mk_delimited(MetaVarKind::Vis, TokenStream::from_ast(vis))
+                        }
                         MatchedSingle(ParseNtResult::Nt(nt)) => {
                             // Other variables are emitted into the output stream as groups with
                             // `Delimiter::Invisible` to maintain parsing priorities.

compiler/rustc_parse/src/parser/mod.rs

@@ -721,6 +721,43 @@ impl<'a> Parser<'a> {
         if !self.eat_keyword(kw) { self.unexpected() } else { Ok(()) }
     }
 
+    /// Consume a sequence produced by a metavar expansion, if present.
+    fn eat_metavar_seq<T>(
+        &mut self,
+        mv_kind: MetaVarKind,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> Option<T> {
+        self.eat_metavar_seq_with_matcher(|mvk| mvk == mv_kind, f)
+    }
+
+    /// A slightly more general form of `eat_metavar_seq`, for use with the
+    /// `MetaVarKind` variants that have parameters, where an exact match isn't
+    /// desired.
+    fn eat_metavar_seq_with_matcher<T>(
+        &mut self,
+        match_mv_kind: impl Fn(MetaVarKind) -> bool,
+        mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> Option<T> {
+        if let token::OpenDelim(delim) = self.token.kind
+            && let Delimiter::Invisible(token::InvisibleOrigin::MetaVar(mv_kind)) = delim
+            && match_mv_kind(mv_kind)
+        {
+            self.bump();
+            let res = f(self).expect("failed to reparse {mv_kind:?}");
+            if let token::CloseDelim(delim) = self.token.kind
+                && let Delimiter::Invisible(token::InvisibleOrigin::MetaVar(mv_kind)) = delim
+                && match_mv_kind(mv_kind)
+            {
+                self.bump();
+                Some(res)
+            } else {
+                panic!("no close delim when reparsing {mv_kind:?}");
+            }
+        } else {
+            None
+        }
+    }
+
     /// Is the given keyword `kw` followed by a non-reserved identifier?
     fn is_kw_followed_by_ident(&self, kw: Symbol) -> bool {
         self.token.is_keyword(kw) && self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
@@ -1462,7 +1499,11 @@ impl<'a> Parser<'a> {
     /// so emit a proper diagnostic.
     // Public for rustfmt usage.
     pub fn parse_visibility(&mut self, fbt: FollowedByType) -> PResult<'a, Visibility> {
-        maybe_whole!(self, NtVis, |vis| vis.into_inner());
+        if let Some(vis) = self
+            .eat_metavar_seq(MetaVarKind::Vis, |this| this.parse_visibility(FollowedByType::Yes))
+        {
+            return Ok(vis);
+        }
 
         if !self.eat_keyword(kw::Pub) {
             // We need a span for our `Spanned<VisibilityKind>`, but there's inherently no
@@ -1700,7 +1741,8 @@ pub enum ParseNtResult {
     Tt(TokenTree),
     Ident(Ident, IdentIsRaw),
     Lifetime(Ident, IdentIsRaw),
+    Vis(P<ast::Visibility>),
 
-    /// This case will eventually be removed, along with `Token::Interpolate`.
+    /// This variant will eventually be removed, along with `Token::Interpolate`.
     Nt(Lrc<Nonterminal>),
 }

compiler/rustc_parse/src/parser/nonterminal.rs

@@ -56,9 +56,7 @@ impl<'a> Parser<'a> {
                 | NtMeta(_)
                 | NtPath(_) => true,
 
-                NtItem(_)
-                | NtBlock(_)
-                | NtVis(_) => false,
+                NtItem(_) | NtBlock(_) => false,
             }
         }
 
@@ -88,7 +86,7 @@ impl<'a> Parser<'a> {
             NonterminalKind::Ident => get_macro_ident(token).is_some(),
             NonterminalKind::Literal => token.can_begin_literal_maybe_minus(),
             NonterminalKind::Vis => match token.kind {
-                // The follow-set of :vis + "priv" keyword + interpolated
+                // The follow-set of :vis + "priv" keyword + interpolated/metavar-expansion.
                 token::Comma
                 | token::Ident(..)
                 | token::NtIdent(..)
@@ -102,7 +100,7 @@ impl<'a> Parser<'a> {
                 token::NtLifetime(..) => true,
                 token::Interpolated(nt) => match &**nt {
                     NtBlock(_) | NtStmt(_) | NtExpr(_) | NtLiteral(_) => true,
-                    NtItem(_) | NtPat(_) | NtTy(_) | NtMeta(_) | NtPath(_) | NtVis(_) => false,
+                    NtItem(_) | NtPat(_) | NtTy(_) | NtMeta(_) | NtPath(_) => false,
                 },
                 token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(k))) => match k {
                     MetaVarKind::Block
@@ -208,8 +206,9 @@ impl<'a> Parser<'a> {
             }
             NonterminalKind::Meta => NtMeta(P(self.parse_attr_item(ForceCollect::Yes)?)),
             NonterminalKind::Vis => {
-                NtVis(P(self
-                    .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?))
+                return Ok(ParseNtResult::Vis(P(self.collect_tokens_no_attrs(|this| {
+                    this.parse_visibility(FollowedByType::Yes)
+                })?)));
             }
             NonterminalKind::Lifetime => {
                 // We want to keep `'keyword` parsing, just like `keyword` is still

tests/ui/macros/block-to-expr-metavar.rs

@@ -0,0 +1,17 @@
+//@ check-pass
+//
+// A test case where a `block` fragment specifier is interpreted as an `expr`
+// fragment specifier. It's an interesting case for the handling of invisible
+// delimiters.
+
+macro_rules! m_expr {
+    ($e:expr) => { const _CURRENT: u32 = $e; };
+}
+
+macro_rules! m_block {
+    ($b:block) => ( m_expr!($b); );
+}
+
+fn main() {
+    m_block!({ 1 });
+}