Rollup merge of #124607 - nnethercote:rustc_expand-cleanups, r=compiler-errors

`rustc_expand` cleanups

Some cleanups I made while looking through this code. Nothing that requires any real domain-specific knowledge about this crate.

r? ````@michaelwoerister````

compiler/rustc_expand/src/base.rs

@@ -21,7 +21,7 @@
 use rustc_session::{parse::ParseSess, Limit, Session};
 use rustc_span::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
+use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId, MacroKind};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{FileName, Span, DUMMY_SP};
@@ -32,8 +32,6 @@
 use std::rc::Rc;
 use thin_vec::ThinVec;
 
-pub(crate) use rustc_span::hygiene::MacroKind;
-
 // When adding new variants, make sure to
 // adjust the `visit_*` / `flat_map_*` calls in `InvocationCollector`
 // to use `assign_id!`
@@ -573,35 +571,6 @@ pub fn raw_expr(sp: Span, guar: Option<ErrorGuaranteed>) -> P<ast::Expr> {
             tokens: None,
         })
     }
-
-    /// A plain dummy pattern.
-    pub fn raw_pat(sp: Span) -> ast::Pat {
-        ast::Pat { id: ast::DUMMY_NODE_ID, kind: PatKind::Wild, span: sp, tokens: None }
-    }
-
-    /// A plain dummy type.
-    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
-        // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
-        // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
-        // support, so we use an empty tuple instead.
-        P(ast::Ty {
-            id: ast::DUMMY_NODE_ID,
-            kind: ast::TyKind::Tup(ThinVec::new()),
-            span: sp,
-            tokens: None,
-        })
-    }
-
-    /// A plain dummy crate.
-    pub fn raw_crate() -> ast::Crate {
-        ast::Crate {
-            attrs: Default::default(),
-            items: Default::default(),
-            spans: Default::default(),
-            id: ast::DUMMY_NODE_ID,
-            is_placeholder: Default::default(),
-        }
-    }
 }
 
 impl MacResult for DummyResult {
@@ -610,7 +579,12 @@ fn make_expr(self: Box<DummyResult>) -> Option<P<ast::Expr>> {
     }
 
     fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
-        Some(P(DummyResult::raw_pat(self.span)))
+        Some(P(ast::Pat {
+            id: ast::DUMMY_NODE_ID,
+            kind: PatKind::Wild,
+            span: self.span,
+            tokens: None,
+        }))
     }
 
     fn make_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
@@ -638,7 +612,15 @@ fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
     }
 
     fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
-        Some(DummyResult::raw_ty(self.span))
+        // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
+        // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
+        // support, so we use an empty tuple instead.
+        Some(P(ast::Ty {
+            id: ast::DUMMY_NODE_ID,
+            kind: ast::TyKind::Tup(ThinVec::new()),
+            span: self.span,
+            tokens: None,
+        }))
     }
 
     fn make_arms(self: Box<DummyResult>) -> Option<SmallVec<[ast::Arm; 1]>> {
@@ -670,7 +652,13 @@ fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
     }
 
     fn make_crate(self: Box<DummyResult>) -> Option<ast::Crate> {
-        Some(DummyResult::raw_crate())
+        Some(ast::Crate {
+            attrs: Default::default(),
+            items: Default::default(),
+            spans: Default::default(),
+            id: ast::DUMMY_NODE_ID,
+            is_placeholder: Default::default(),
+        })
     }
 }
 

compiler/rustc_expand/src/build.rs

@@ -175,20 +175,6 @@ pub fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt {
         ast::Stmt { id: ast::DUMMY_NODE_ID, span: expr.span, kind: ast::StmtKind::Expr(expr) }
     }
 
-    pub fn stmt_let_pat(&self, sp: Span, pat: P<ast::Pat>, ex: P<ast::Expr>) -> ast::Stmt {
-        let local = P(ast::Local {
-            pat,
-            ty: None,
-            id: ast::DUMMY_NODE_ID,
-            kind: LocalKind::Init(ex),
-            span: sp,
-            colon_sp: None,
-            attrs: AttrVec::new(),
-            tokens: None,
-        });
-        self.stmt_local(local, sp)
-    }
-
     pub fn stmt_let(&self, sp: Span, mutbl: bool, ident: Ident, ex: P<ast::Expr>) -> ast::Stmt {
         self.stmt_let_ty(sp, mutbl, ident, None, ex)
     }
@@ -278,10 +264,6 @@ pub fn expr_self(&self, span: Span) -> P<ast::Expr> {
         self.expr_ident(span, Ident::with_dummy_span(kw::SelfLower))
     }
 
-    pub fn expr_field(&self, span: Span, expr: P<Expr>, field: Ident) -> P<ast::Expr> {
-        self.expr(span, ast::ExprKind::Field(expr, field))
-    }
-
     pub fn expr_macro_call(&self, span: Span, call: P<ast::MacCall>) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::MacCall(call))
     }
@@ -394,11 +376,6 @@ pub fn expr_str(&self, span: Span, s: Symbol) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_char(&self, span: Span, ch: char) -> P<ast::Expr> {
-        let lit = token::Lit::new(token::Char, literal::escape_char_symbol(ch), None);
-        self.expr(span, ast::ExprKind::Lit(lit))
-    }
-
     pub fn expr_byte_str(&self, span: Span, bytes: Vec<u8>) -> P<ast::Expr> {
         let lit = token::Lit::new(token::ByteStr, literal::escape_byte_str_symbol(&bytes), None);
         self.expr(span, ast::ExprKind::Lit(lit))
@@ -414,10 +391,6 @@ pub fn expr_array_ref(&self, sp: Span, exprs: ThinVec<P<ast::Expr>>) -> P<ast::E
         self.expr_addr_of(sp, self.expr_array(sp, exprs))
     }
 
-    pub fn expr_cast(&self, sp: Span, expr: P<ast::Expr>, ty: P<ast::Ty>) -> P<ast::Expr> {
-        self.expr(sp, ast::ExprKind::Cast(expr, ty))
-    }
-
     pub fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
         let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         self.expr_call_global(sp, some, thin_vec![expr])

compiler/rustc_expand/src/config.rs

@@ -99,10 +99,11 @@ fn feature_list(attr: &Attribute) -> ThinVec<ast::NestedMetaItem> {
             // If the declared feature is unstable, record it.
             if let Some(f) = UNSTABLE_FEATURES.iter().find(|f| name == f.feature.name) {
                 (f.set_enabled)(&mut features);
-                // When the ICE comes from core, alloc or std (approximation of the standard library), there's a chance
+                // When the ICE comes from core, alloc or std (approximation of the standard
-                // that the person hitting the ICE may be using -Zbuild-std or similar with an untested target.
+                // library), there's a chance that the person hitting the ICE may be using
-                // The bug is probably in the standard library and not the compiler in that case, but that doesn't
+                // -Zbuild-std or similar with an untested target. The bug is probably in the
-                // really matter - we want a bug report.
+                // standard library and not the compiler in that case, but that doesn't really
+                // matter - we want a bug report.
                 if features.internal(name)
                     && ![sym::core, sym::alloc, sym::std].contains(&crate_name)
                 {

compiler/rustc_expand/src/expand.rs

@@ -4,7 +4,6 @@
     IncompleteParse, RecursionLimitReached, RemoveExprNotSupported, RemoveNodeNotSupported,
     UnsupportedKeyValue, WrongFragmentKind,
 };
-use crate::hygiene::SyntaxContext;
 use crate::mbe::diagnostics::annotate_err_with_kind;
 use crate::module::{mod_dir_path, parse_external_mod, DirOwnership, ParsedExternalMod};
 use crate::placeholders::{placeholder, PlaceholderExpander};
@@ -32,6 +31,7 @@
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::parse::feature_err;
 use rustc_session::{Limit, Session};
+use rustc_span::hygiene::SyntaxContext;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{ErrorGuaranteed, FileName, LocalExpnId, Span};
 
@@ -87,7 +87,7 @@ fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
         }
 
         impl AstFragment {
-            pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
+            fn add_placeholders(&mut self, placeholders: &[NodeId]) {
                 if placeholders.is_empty() {
                     return;
                 }
@@ -100,14 +100,14 @@ pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
                 }
             }
 
-            pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
+            pub(crate) fn make_opt_expr(self) -> Option<P<ast::Expr>> {
                 match self {
                     AstFragment::OptExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
                 }
             }
 
-            pub fn make_method_receiver_expr(self) -> P<ast::Expr> {
+            pub(crate) fn make_method_receiver_expr(self) -> P<ast::Expr> {
                 match self {
                     AstFragment::MethodReceiverExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
@@ -125,7 +125,7 @@ fn make_ast<T: InvocationCollectorNode>(self) -> T::OutputTy {
                 T::fragment_to_output(self)
             }
 
-            pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
+            pub(crate) fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
                 match self {
                     AstFragment::OptExpr(opt_expr) => {
                         visit_clobber(opt_expr, |opt_expr| {
@@ -372,6 +372,14 @@ pub fn span(&self) -> Span {
             InvocationKind::Derive { path, .. } => path.span,
         }
     }
+
+    fn span_mut(&mut self) -> &mut Span {
+        match &mut self.kind {
+            InvocationKind::Bang { span, .. } => span,
+            InvocationKind::Attr { attr, .. } => &mut attr.span,
+            InvocationKind::Derive { path, .. } => &mut path.span,
+        }
+    }
 }
 
 pub struct MacroExpander<'a, 'b> {
@@ -432,7 +440,8 @@ pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragm
                     break;
                 }
                 invocations = mem::take(&mut undetermined_invocations);
-                force = !mem::replace(&mut progress, false);
+                force = !progress;
+                progress = false;
                 if force && self.monotonic {
                     self.cx.dcx().span_delayed_bug(
                         invocations.last().unwrap().0.span(),
@@ -471,7 +480,7 @@ pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragm
             self.cx.force_mode = force;
 
             let fragment_kind = invoc.fragment_kind;
-            let (expanded_fragment, new_invocations) = match self.expand_invoc(invoc, &ext.kind) {
+            match self.expand_invoc(invoc, &ext.kind) {
                 ExpandResult::Ready(fragment) => {
                     let mut derive_invocations = Vec::new();
                     let derive_placeholders = self
@@ -503,12 +512,19 @@ pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragm
                         })
                         .unwrap_or_default();
 
-                    let (fragment, collected_invocations) =
+                    let (expanded_fragment, collected_invocations) =
                         self.collect_invocations(fragment, &derive_placeholders);
-                    // We choose to expand any derive invocations associated with this macro invocation
+                    // We choose to expand any derive invocations associated with this macro
-                    // *before* any macro invocations collected from the output fragment
+                    // invocation *before* any macro invocations collected from the output
+                    // fragment.
                     derive_invocations.extend(collected_invocations);
-                    (fragment, derive_invocations)
+
+                    progress = true;
+                    if expanded_fragments.len() < depth {
+                        expanded_fragments.push(Vec::new());
+                    }
+                    expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
+                    invocations.extend(derive_invocations.into_iter().rev());
                 }
                 ExpandResult::Retry(invoc) => {
                     if force {
@@ -519,17 +535,9 @@ pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragm
                     } else {
                         // Cannot expand, will retry this invocation later.
                         undetermined_invocations.push((invoc, Some(ext)));
-                        continue;
                     }
                 }
-            };
-
-            progress = true;
-            if expanded_fragments.len() < depth {
-                expanded_fragments.push(Vec::new());
             }
-            expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
-            invocations.extend(new_invocations.into_iter().rev());
         }
 
         self.cx.current_expansion = orig_expansion_data;
@@ -590,11 +598,7 @@ fn collect_invocations(
                 for (invoc, _) in invocations.iter_mut() {
                     let expn_id = invoc.expansion_data.id;
                     let parent_def = self.cx.resolver.invocation_parent(expn_id);
-                    let span = match &mut invoc.kind {
+                    let span = invoc.span_mut();
-                        InvocationKind::Bang { span, .. } => span,
-                        InvocationKind::Attr { attr, .. } => &mut attr.span,
-                        InvocationKind::Derive { path, .. } => &mut path.span,
-                    };
                     *span = span.with_parent(Some(parent_def));
                 }
             }
@@ -957,7 +961,7 @@ pub fn parse_ast_fragment<'a>(
     })
 }
 
-pub fn ensure_complete_parse<'a>(
+pub(crate) fn ensure_complete_parse<'a>(
     parser: &Parser<'a>,
     macro_path: &ast::Path,
     kind_name: &str,

compiler/rustc_expand/src/lib.rs

@@ -1,43 +1,39 @@
+// tidy-alphabetical-start
+#![allow(internal_features)]
+#![allow(rustc::diagnostic_outside_of_impl)]
 #![doc(rust_logo)]
-#![feature(rustdoc_internals)]
 #![feature(array_windows)]
 #![feature(associated_type_defaults)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
-#![feature(lint_reasons)]
 #![feature(macro_metavar_expr)]
 #![feature(map_try_insert)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]
-#![feature(proc_macro_span)]
+#![feature(rustdoc_internals)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
-#![allow(rustc::diagnostic_outside_of_impl)]
+// tidy-alphabetical-end
-#![allow(internal_features)]
 
 extern crate proc_macro as pm;
 
+mod build;
+mod errors;
+// FIXME(Nilstrieb) Translate macro_rules diagnostics
+#[allow(rustc::untranslatable_diagnostic)]
+mod mbe;
 mod placeholders;
 mod proc_macro_server;
 
 pub use mbe::macro_rules::compile_declarative_macro;
-pub(crate) use rustc_span::hygiene;
 pub mod base;
-pub mod build;
-#[macro_use]
 pub mod config;
-pub mod errors;
 pub mod expand;
 pub mod module;
-
 // FIXME(Nilstrieb) Translate proc_macro diagnostics
 #[allow(rustc::untranslatable_diagnostic)]
 pub mod proc_macro;
 
-// FIXME(Nilstrieb) Translate macro_rules diagnostics
-#[allow(rustc::untranslatable_diagnostic)]
-pub(crate) mod mbe;
-
 // HACK(Centril, #64197): These shouldn't really be here.
 // Rather, they should be with their respective modules which are defined in other crates.
 // However, since for now constructing a `ParseSess` sorta requires `config` from this crate,

compiler/rustc_expand/src/mbe.rs

@@ -4,12 +4,13 @@
 //! official terminology: "declarative macros".
 
 pub(crate) mod diagnostics;
-pub(crate) mod macro_check;
-pub(crate) mod macro_parser;
 pub(crate) mod macro_rules;
-pub(crate) mod metavar_expr;
+
-pub(crate) mod quoted;
+mod macro_check;
-pub(crate) mod transcribe;
+mod macro_parser;
+mod metavar_expr;
+mod quoted;
+mod transcribe;
 
 use metavar_expr::MetaVarExpr;
 use rustc_ast::token::{Delimiter, NonterminalKind, Token, TokenKind};

compiler/rustc_expand/src/mbe/diagnostics.rs

@@ -28,7 +28,8 @@ pub(super) fn failed_to_match_macro<'cx>(
 ) -> Box<dyn MacResult + 'cx> {
     let psess = &cx.sess.psess;
 
-    // An error occurred, try the expansion again, tracking the expansion closely for better diagnostics.
+    // An error occurred, try the expansion again, tracking the expansion closely for better
+    // diagnostics.
     let mut tracker = CollectTrackerAndEmitter::new(cx, sp);
 
     let try_success_result = try_match_macro(psess, name, &arg, lhses, &mut tracker);

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -157,8 +157,8 @@ pub(super) trait Tracker<'matcher> {
     /// This is called before trying to match next MatcherLoc on the current token.
     fn before_match_loc(&mut self, _parser: &TtParser, _matcher: &'matcher MatcherLoc) {}
 
-    /// This is called after an arm has been parsed, either successfully or unsuccessfully. When this is called,
+    /// This is called after an arm has been parsed, either successfully or unsuccessfully. When
-    /// `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
+    /// this is called, `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
     fn after_arm(&mut self, _result: &NamedParseResult<Self::Failure>) {}
 
     /// For tracing.
@@ -169,7 +169,8 @@ fn recovery() -> Recovery {
     }
 }
 
-/// A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to monomorphization.
+/// A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to
+/// monomorphization.
 pub(super) struct NoopTracker;
 
 impl<'matcher> Tracker<'matcher> for NoopTracker {
@@ -492,7 +493,7 @@ pub fn compile_declarative_macro(
                     .pop()
                     .unwrap();
                     // We don't handle errors here, the driver will abort
-                    // after parsing/expansion. we can report every error in every macro this way.
+                    // after parsing/expansion. We can report every error in every macro this way.
                     check_emission(check_lhs_nt_follows(sess, def, &tt));
                     return tt;
                 }
@@ -528,7 +529,7 @@ pub fn compile_declarative_macro(
         check_emission(check_rhs(sess, rhs));
     }
 
-    // don't abort iteration early, so that errors for multiple lhses can be reported
+    // Don't abort iteration early, so that errors for multiple lhses can be reported.
     for lhs in &lhses {
         check_emission(check_lhs_no_empty_seq(sess, slice::from_ref(lhs)));
     }

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -39,26 +39,32 @@ fn visit_span(&mut self, span: &mut Span) {
 }
 
 /// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
-enum Frame<'a> {
+struct Frame<'a> {
-    Delimited {
+    tts: &'a [mbe::TokenTree],
-        tts: &'a [mbe::TokenTree],
+    idx: usize,
-        idx: usize,
+    kind: FrameKind,
-        delim: Delimiter,
+}
-        span: DelimSpan,
+
-        spacing: DelimSpacing,
+enum FrameKind {
-    },
+    Delimited { delim: Delimiter, span: DelimSpan, spacing: DelimSpacing },
-    Sequence {
+    Sequence { sep: Option<Token>, kleene_op: KleeneOp },
-        tts: &'a [mbe::TokenTree],
-        idx: usize,
-        sep: Option<Token>,
-        kleene_op: KleeneOp,
-    },
 }
 
 impl<'a> Frame<'a> {
-    /// Construct a new frame around the delimited set of tokens.
+    fn new_delimited(src: &'a mbe::Delimited, span: DelimSpan, spacing: DelimSpacing) -> Frame<'a> {
-    fn new(src: &'a mbe::Delimited, span: DelimSpan, spacing: DelimSpacing) -> Frame<'a> {
+        Frame {
-        Frame::Delimited { tts: &src.tts, idx: 0, delim: src.delim, span, spacing }
+            tts: &src.tts,
+            idx: 0,
+            kind: FrameKind::Delimited { delim: src.delim, span, spacing },
+        }
+    }
+
+    fn new_sequence(
+        src: &'a mbe::SequenceRepetition,
+        sep: Option<Token>,
+        kleene_op: KleeneOp,
+    ) -> Frame<'a> {
+        Frame { tts: &src.tts, idx: 0, kind: FrameKind::Sequence { sep, kleene_op } }
     }
 }
 
@@ -66,13 +72,9 @@ impl<'a> Iterator for Frame<'a> {
     type Item = &'a mbe::TokenTree;
 
     fn next(&mut self) -> Option<&'a mbe::TokenTree> {
-        match self {
+        let res = self.tts.get(self.idx);
-            Frame::Delimited { tts, idx, .. } | Frame::Sequence { tts, idx, .. } => {
+        self.idx += 1;
-                let res = tts.get(*idx);
+        res
-                *idx += 1;
-                res
-            }
-        }
     }
 }
 
@@ -111,13 +113,16 @@ pub(super) fn transcribe<'a>(
     // We descend into the RHS (`src`), expanding things as we go. This stack contains the things
     // we have yet to expand/are still expanding. We start the stack off with the whole RHS. The
     // choice of spacing values doesn't matter.
-    let mut stack: SmallVec<[Frame<'_>; 1]> =
+    let mut stack: SmallVec<[Frame<'_>; 1]> = smallvec![Frame::new_delimited(
-        smallvec![Frame::new(src, src_span, DelimSpacing::new(Spacing::Alone, Spacing::Alone))];
+        src,
+        src_span,
+        DelimSpacing::new(Spacing::Alone, Spacing::Alone)
+    )];
 
     // As we descend in the RHS, we will need to be able to match nested sequences of matchers.
     // `repeats` keeps track of where we are in matching at each level, with the last element being
     // the most deeply nested sequence. This is used as a stack.
-    let mut repeats = Vec::new();
+    let mut repeats: Vec<(usize, usize)> = Vec::new();
 
     // `result` contains resulting token stream from the TokenTree we just finished processing. At
     // the end, this will contain the full result of transcription, but at arbitrary points during
@@ -142,11 +147,12 @@ pub(super) fn transcribe<'a>(
 
             // Otherwise, if we have just reached the end of a sequence and we can keep repeating,
             // go back to the beginning of the sequence.
-            if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
+            let frame = stack.last_mut().unwrap();
+            if let FrameKind::Sequence { sep, .. } = &frame.kind {
                 let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
                 *repeat_idx += 1;
                 if repeat_idx < repeat_len {
-                    *idx = 0;
+                    frame.idx = 0;
                     if let Some(sep) = sep {
                         result.push(TokenTree::Token(sep.clone(), Spacing::Alone));
                     }
@@ -157,16 +163,16 @@ pub(super) fn transcribe<'a>(
             // We are done with the top of the stack. Pop it. Depending on what it was, we do
             // different things. Note that the outermost item must be the delimited, wrapped RHS
             // that was passed in originally to `transcribe`.
-            match stack.pop().unwrap() {
+            match stack.pop().unwrap().kind {
                 // Done with a sequence. Pop from repeats.
-                Frame::Sequence { .. } => {
+                FrameKind::Sequence { .. } => {
                     repeats.pop();
                 }
 
                 // We are done processing a Delimited. If this is the top-level delimited, we are
                 // done. Otherwise, we unwind the result_stack to append what we have produced to
                 // any previous results.
-                Frame::Delimited { delim, span, mut spacing, .. } => {
+                FrameKind::Delimited { delim, span, mut spacing, .. } => {
                     // Hack to force-insert a space after `]` in certain case.
                     // See discussion of the `hex-literal` crate in #114571.
                     if delim == Delimiter::Bracket {
@@ -192,7 +198,7 @@ pub(super) fn transcribe<'a>(
             // We are descending into a sequence. We first make sure that the matchers in the RHS
             // and the matches in `interp` have the same shape. Otherwise, either the caller or the
             // macro writer has made a mistake.
-            seq @ mbe::TokenTree::Sequence(_, delimited) => {
+            seq @ mbe::TokenTree::Sequence(_, seq_rep) => {
                 match lockstep_iter_size(seq, interp, &repeats) {
                     LockstepIterSize::Unconstrained => {
                         return Err(cx
@@ -233,12 +239,11 @@ pub(super) fn transcribe<'a>(
                             // The first time we encounter the sequence we push it to the stack. It
                             // then gets reused (see the beginning of the loop) until we are done
                             // repeating.
-                            stack.push(Frame::Sequence {
+                            stack.push(Frame::new_sequence(
-                                idx: 0,
+                                seq_rep,
-                                sep: seq.separator.clone(),
+                                seq.separator.clone(),
-                                tts: &delimited.tts,
+                                seq.kleene.op,
-                                kleene_op: seq.kleene.op,
+                            ));
-                            });
                         }
                     }
                 }
@@ -294,13 +299,7 @@ pub(super) fn transcribe<'a>(
             // the previous results (from outside the Delimited).
             mbe::TokenTree::Delimited(mut span, spacing, delimited) => {
                 mut_visit::visit_delim_span(&mut span, &mut marker);
-                stack.push(Frame::Delimited {
+                stack.push(Frame::new_delimited(delimited, span, *spacing));
-                    tts: &delimited.tts,
-                    delim: delimited.delim,
-                    idx: 0,
-                    span,
-                    spacing: *spacing,
-                });
                 result_stack.push(mem::take(&mut result));
             }
 
@@ -358,10 +357,13 @@ fn maybe_use_metavar_location(
 ) -> TokenTree {
     let undelimited_seq = matches!(
         stack.last(),
-        Some(Frame::Sequence {
+        Some(Frame {
             tts: [_],
-            sep: None,
+            kind: FrameKind::Sequence {
-            kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
+                sep: None,
+                kleene_op: KleeneOp::ZeroOrMore | KleeneOp::OneOrMore,
+                ..
+            },
             ..
         })
     );

compiler/rustc_expand/src/placeholders.rs

@@ -9,7 +9,7 @@
 use smallvec::{smallvec, SmallVec};
 use thin_vec::ThinVec;
 
-pub fn placeholder(
+pub(crate) fn placeholder(
     kind: AstFragmentKind,
     id: ast::NodeId,
     vis: Option<ast::Visibility>,