1 //! `hir_expand` deals with macro expansion.
3 //! Specifically, it implements a concept of `MacroFile` -- a file whose syntax
4 //! tree originates not from the text of some `FileId`, but from some macro
11 pub mod builtin_attr_macro;
12 pub mod builtin_derive_macro;
13 pub mod builtin_fn_macro;
18 use base_db::ProcMacroKind;
21 pub use mbe::{ExpandError, ExpandResult};
23 use std::{hash::Hash, iter, sync::Arc};
25 use base_db::{impl_intern_key, salsa, CrateId, FileId, FileRange};
27 algo::skip_trivia_token,
28 ast::{self, AstNode, HasAttrs},
29 Direction, SyntaxNode, SyntaxToken, TextRange,
33 ast_id_map::FileAstId,
34 builtin_attr_macro::BuiltinAttrExpander,
35 builtin_derive_macro::BuiltinDeriveExpander,
36 builtin_fn_macro::{BuiltinFnLikeExpander, EagerExpander},
38 proc_macro::ProcMacroExpander,
44 /// Input to the analyzer is a set of files, where each file is identified by
45 /// `FileId` and contains source code. However, another source of source code in
46 /// Rust are macros: each macro can be thought of as producing a "temporary
47 /// file". To assign an id to such a file, we use the id of the macro call that
48 /// produced the file. So, a `HirFileId` is either a `FileId` (source code
49 /// written by user), or a `MacroCallId` (source code produced by macro).
51 /// What is a `MacroCallId`? Simplifying, it's a `HirFileId` of a file
52 /// containing the call plus the offset of the macro call in the file. Note that
53 /// this is a recursive definition! However, the size_of of `HirFileId` is
54 /// finite (because everything bottoms out at the real `FileId`) and small
55 /// (`MacroCallId` uses the location interning. You can check details here:
56 /// <https://en.wikipedia.org/wiki/String_interning>).
57 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
58 pub struct HirFileId(HirFileIdRepr);
60 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
65 impl From<FileId> for HirFileId {
66 fn from(id: FileId) -> Self {
67 HirFileId(HirFileIdRepr::FileId(id))
70 impl From<MacroFile> for HirFileId {
71 fn from(id: MacroFile) -> Self {
72 HirFileId(HirFileIdRepr::MacroFile(id))
76 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
77 pub struct MacroFile {
78 pub macro_call_id: MacroCallId,
81 /// `MacroCallId` identifies a particular macro invocation, like
82 /// `println!("Hello, {}", world)`.
83 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
84 pub struct MacroCallId(salsa::InternId);
85 impl_intern_key!(MacroCallId);
87 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
88 pub struct MacroCallLoc {
90 pub(crate) krate: CrateId,
91 eager: Option<EagerCallInfo>,
92 pub kind: MacroCallKind,
95 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
96 pub struct MacroDefId {
98 pub kind: MacroDefKind,
99 pub local_inner: bool,
102 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
103 pub enum MacroDefKind {
104 Declarative(AstId<ast::Macro>),
105 BuiltIn(BuiltinFnLikeExpander, AstId<ast::Macro>),
106 // FIXME: maybe just Builtin and rename BuiltinFnLikeExpander to BuiltinExpander
107 BuiltInAttr(BuiltinAttrExpander, AstId<ast::Macro>),
108 BuiltInDerive(BuiltinDeriveExpander, AstId<ast::Macro>),
109 BuiltInEager(EagerExpander, AstId<ast::Macro>),
110 ProcMacro(ProcMacroExpander, ProcMacroKind, AstId<ast::Fn>),
113 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
114 struct EagerCallInfo {
115 /// NOTE: This can be *either* the expansion result, *or* the argument to the eager macro!
116 arg_or_expansion: Arc<tt::Subtree>,
117 included_file: Option<FileId>,
120 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
121 pub enum MacroCallKind {
123 ast_id: AstId<ast::MacroCall>,
127 ast_id: AstId<ast::Item>,
129 /// Syntactical index of the invoking `#[derive]` attribute.
131 /// Outer attributes are counted first, then inner attributes. This does not support
132 /// out-of-line modules, which may have attributes spread across 2 files!
133 derive_attr_index: u32,
136 ast_id: AstId<ast::Item>,
138 attr_args: (tt::Subtree, mbe::TokenMap),
139 /// Syntactical index of the invoking `#[attribute]`.
141 /// Outer attributes are counted first, then inner attributes. This does not support
142 /// out-of-line modules, which may have attributes spread across 2 files!
143 invoc_attr_index: u32,
148 /// For macro-expansion files, returns the file original source file the
149 /// expansion originated from.
150 pub fn original_file(self, db: &dyn db::AstDatabase) -> FileId {
152 HirFileIdRepr::FileId(file_id) => file_id,
153 HirFileIdRepr::MacroFile(macro_file) => {
154 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
155 let file_id = match &loc.eager {
156 Some(EagerCallInfo { included_file: Some(file), .. }) => (*file).into(),
157 _ => loc.kind.file_id(),
159 file_id.original_file(db)
164 pub fn expansion_level(self, db: &dyn db::AstDatabase) -> u32 {
167 while let HirFileIdRepr::MacroFile(macro_file) = curr.0 {
168 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
171 curr = loc.kind.file_id();
176 /// If this is a macro call, returns the syntax node of the call.
177 pub fn call_node(self, db: &dyn db::AstDatabase) -> Option<InFile<SyntaxNode>> {
179 HirFileIdRepr::FileId(_) => None,
180 HirFileIdRepr::MacroFile(macro_file) => {
181 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
182 Some(loc.kind.to_node(db))
187 /// Return expansion information if it is a macro-expansion file
188 pub fn expansion_info(self, db: &dyn db::AstDatabase) -> Option<ExpansionInfo> {
190 HirFileIdRepr::FileId(_) => None,
191 HirFileIdRepr::MacroFile(macro_file) => {
192 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
194 let arg_tt = loc.kind.arg(db)?;
196 let def = loc.def.ast_id().left().and_then(|id| {
197 let def_tt = match id.to_node(db) {
198 ast::Macro::MacroRules(mac) => mac.token_tree()?,
199 ast::Macro::MacroDef(mac) => mac.body()?,
201 Some(InFile::new(id.file_id, def_tt))
203 let attr_input_or_mac_def = def.or_else(|| match loc.kind {
204 MacroCallKind::Attr { ast_id, invoc_attr_index, .. } => {
208 .nth(invoc_attr_index as usize)?
210 Some(InFile::new(ast_id.file_id, tt))
215 let macro_def = db.macro_def(loc.def).ok()?;
216 let (parse, exp_map) = db.parse_macro_expansion(macro_file).value?;
217 let macro_arg = db.macro_arg(macro_file.macro_call_id)?;
220 expanded: InFile::new(self, parse.syntax_node()),
221 arg: InFile::new(loc.kind.file_id(), arg_tt),
222 attr_input_or_mac_def,
223 macro_arg_shift: mbe::Shift::new(¯o_arg.0),
232 /// Indicate it is macro file generated for builtin derive
233 pub fn is_builtin_derive(&self, db: &dyn db::AstDatabase) -> Option<InFile<ast::Item>> {
235 HirFileIdRepr::FileId(_) => None,
236 HirFileIdRepr::MacroFile(macro_file) => {
237 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
238 let item = match loc.def.kind {
239 MacroDefKind::BuiltInDerive(..) => loc.kind.to_node(db),
242 Some(item.with_value(ast::Item::cast(item.value.clone())?))
247 pub fn is_custom_derive(&self, db: &dyn db::AstDatabase) -> bool {
249 HirFileIdRepr::FileId(_) => false,
250 HirFileIdRepr::MacroFile(macro_file) => {
251 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
253 MacroDefKind::ProcMacro(_, ProcMacroKind::CustomDerive, _) => true,
260 /// Return whether this file is an include macro
261 pub fn is_include_macro(&self, db: &dyn db::AstDatabase) -> bool {
263 HirFileIdRepr::MacroFile(macro_file) => {
264 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
265 matches!(loc.eager, Some(EagerCallInfo { included_file: Some(_), .. }))
271 /// Return whether this file is an include macro
272 pub fn is_attr_macro(&self, db: &dyn db::AstDatabase) -> bool {
274 HirFileIdRepr::MacroFile(macro_file) => {
275 let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
276 matches!(loc.kind, MacroCallKind::Attr { .. })
282 pub fn is_macro(self) -> bool {
283 matches!(self.0, HirFileIdRepr::MacroFile(_))
288 pub fn as_lazy_macro(
290 db: &dyn db::AstDatabase,
294 db.intern_macro(MacroCallLoc { def: self, krate, eager: None, kind })
297 pub fn ast_id(&self) -> Either<AstId<ast::Macro>, AstId<ast::Fn>> {
298 let id = match &self.kind {
299 MacroDefKind::ProcMacro(.., id) => return Either::Right(*id),
300 MacroDefKind::Declarative(id)
301 | MacroDefKind::BuiltIn(_, id)
302 | MacroDefKind::BuiltInAttr(_, id)
303 | MacroDefKind::BuiltInDerive(_, id)
304 | MacroDefKind::BuiltInEager(_, id) => id,
309 pub fn is_proc_macro(&self) -> bool {
310 matches!(self.kind, MacroDefKind::ProcMacro(..))
314 // FIXME: attribute indices do not account for `cfg_attr`, which means that we'll strip the whole
315 // `cfg_attr` instead of just one of the attributes it expands to
318 /// Returns the file containing the macro invocation.
319 fn file_id(&self) -> HirFileId {
321 MacroCallKind::FnLike { ast_id, .. } => ast_id.file_id,
322 MacroCallKind::Derive { ast_id, .. } | MacroCallKind::Attr { ast_id, .. } => {
328 pub fn to_node(&self, db: &dyn db::AstDatabase) -> InFile<SyntaxNode> {
330 MacroCallKind::FnLike { ast_id, .. } => {
331 ast_id.with_value(ast_id.to_node(db).syntax().clone())
333 MacroCallKind::Derive { ast_id, .. } | MacroCallKind::Attr { ast_id, .. } => {
334 ast_id.with_value(ast_id.to_node(db).syntax().clone())
339 fn arg(&self, db: &dyn db::AstDatabase) -> Option<SyntaxNode> {
341 MacroCallKind::FnLike { ast_id, .. } => {
342 Some(ast_id.to_node(db).token_tree()?.syntax().clone())
344 MacroCallKind::Derive { ast_id, .. } | MacroCallKind::Attr { ast_id, .. } => {
345 Some(ast_id.to_node(db).syntax().clone())
350 fn expand_to(&self) -> ExpandTo {
352 MacroCallKind::FnLike { expand_to, .. } => *expand_to,
353 MacroCallKind::Derive { .. } => ExpandTo::Items,
354 MacroCallKind::Attr { .. } => ExpandTo::Items, // is this always correct?
360 pub fn as_file(self) -> HirFileId {
361 MacroFile { macro_call_id: self }.into()
365 /// ExpansionInfo mainly describes how to map text range between src and expanded macro
366 #[derive(Debug, Clone, PartialEq, Eq)]
367 pub struct ExpansionInfo {
368 expanded: InFile<SyntaxNode>,
369 arg: InFile<SyntaxNode>,
370 /// The `macro_rules!` arguments or attribute input.
371 attr_input_or_mac_def: Option<InFile<ast::TokenTree>>,
373 macro_def: Arc<TokenExpander>,
374 macro_arg: Arc<(tt::Subtree, mbe::TokenMap)>,
375 macro_arg_shift: mbe::Shift,
376 exp_map: Arc<mbe::TokenMap>,
382 pub fn call_node(&self) -> Option<InFile<SyntaxNode>> {
383 Some(self.arg.with_value(self.arg.value.parent()?))
386 pub fn map_token_down(
388 db: &dyn db::AstDatabase,
389 item: Option<ast::Item>,
390 token: InFile<&SyntaxToken>,
391 ) -> Option<impl Iterator<Item = InFile<SyntaxToken>> + '_> {
392 assert_eq!(token.file_id, self.arg.file_id);
393 let token_id = if let Some(item) = item {
394 // check if we are mapping down in an attribute input
395 let call_id = match self.expanded.file_id.0 {
396 HirFileIdRepr::FileId(_) => return None,
397 HirFileIdRepr::MacroFile(macro_file) => macro_file.macro_call_id,
399 let loc = db.lookup_intern_macro(call_id);
401 let token_range = token.value.text_range();
403 MacroCallKind::Attr { attr_args, invoc_attr_index, .. } => {
404 let attr = item.attrs().nth(*invoc_attr_index as usize)?;
405 match attr.token_tree() {
407 if token_tree.syntax().text_range().contains_range(token_range) =>
409 let attr_input_start =
410 token_tree.left_delimiter_token()?.text_range().start();
411 let range = token.value.text_range().checked_sub(attr_input_start)?;
413 self.macro_arg_shift.shift(attr_args.1.token_by_range(range)?);
425 let token_id = match token_id {
426 Some(token_id) => token_id,
429 token.value.text_range().checked_sub(self.arg.value.text_range().start())?;
430 let token_id = self.macro_arg.1.token_by_range(range)?;
431 self.macro_def.map_id_down(token_id)
437 .ranges_by_token(token_id, token.value.kind())
438 .flat_map(move |range| self.expanded.value.covering_element(range).into_token());
440 Some(tokens.map(move |token| self.expanded.with_value(token)))
445 db: &dyn db::AstDatabase,
446 token: InFile<&SyntaxToken>,
447 ) -> Option<(InFile<SyntaxToken>, Origin)> {
448 let token_id = self.exp_map.token_by_range(token.value.text_range())?;
449 let (mut token_id, origin) = self.macro_def.map_id_up(token_id);
451 let call_id = match self.expanded.file_id.0 {
452 HirFileIdRepr::FileId(_) => return None,
453 HirFileIdRepr::MacroFile(macro_file) => macro_file.macro_call_id,
455 let loc = db.lookup_intern_macro(call_id);
457 let (token_map, tt) = match &loc.kind {
458 MacroCallKind::Attr { attr_args, .. } => match self.macro_arg_shift.unshift(token_id) {
460 token_id = unshifted;
461 (&attr_args.1, self.attr_input_or_mac_def.clone()?.syntax().cloned())
463 None => (&self.macro_arg.1, self.arg.clone()),
466 mbe::Origin::Call => (&self.macro_arg.1, self.arg.clone()),
467 mbe::Origin::Def => match (&*self.macro_def, &self.attr_input_or_mac_def) {
469 TokenExpander::MacroRules { def_site_token_map, .. }
470 | TokenExpander::MacroDef { def_site_token_map, .. },
472 ) => (def_site_token_map, tt.syntax().cloned()),
473 _ => panic!("`Origin::Def` used with non-`macro_rules!` macro"),
478 let range = token_map.first_range_by_token(token_id, token.value.kind())?;
480 tt.value.covering_element(range + tt.value.text_range().start()).into_token()?;
481 Some((tt.with_value(token), origin))
485 /// `AstId` points to an AST node in any file.
487 /// It is stable across reparses, and can be used as salsa key/value.
488 // FIXME: isn't this just a `Source<FileAstId<N>>` ?
489 pub type AstId<N> = InFile<FileAstId<N>>;
491 impl<N: AstNode> AstId<N> {
492 pub fn to_node(&self, db: &dyn db::AstDatabase) -> N {
493 let root = db.parse_or_expand(self.file_id).unwrap();
494 db.ast_id_map(self.file_id).get(self.value).to_node(&root)
498 /// `InFile<T>` stores a value of `T` inside a particular file/syntax tree.
500 /// Typical usages are:
502 /// * `InFile<SyntaxNode>` -- syntax node in a file
503 /// * `InFile<ast::FnDef>` -- ast node in a file
504 /// * `InFile<TextSize>` -- offset in a file
505 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
506 pub struct InFile<T> {
507 pub file_id: HirFileId,
512 pub fn new(file_id: HirFileId, value: T) -> InFile<T> {
513 InFile { file_id, value }
516 // Similarly, naming here is stupid...
517 pub fn with_value<U>(&self, value: U) -> InFile<U> {
518 InFile::new(self.file_id, value)
521 pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> InFile<U> {
522 InFile::new(self.file_id, f(self.value))
524 pub fn as_ref(&self) -> InFile<&T> {
525 self.with_value(&self.value)
527 pub fn file_syntax(&self, db: &dyn db::AstDatabase) -> SyntaxNode {
528 db.parse_or_expand(self.file_id).expect("source created from invalid file")
532 impl<T: Clone> InFile<&T> {
533 pub fn cloned(&self) -> InFile<T> {
534 self.with_value(self.value.clone())
538 impl<T> InFile<Option<T>> {
539 pub fn transpose(self) -> Option<InFile<T>> {
540 let value = self.value?;
541 Some(InFile::new(self.file_id, value))
545 impl InFile<SyntaxNode> {
546 pub fn ancestors_with_macros(
548 db: &dyn db::AstDatabase,
549 ) -> impl Iterator<Item = InFile<SyntaxNode>> + Clone + '_ {
550 iter::successors(Some(self), move |node| match node.value.parent() {
551 Some(parent) => Some(node.with_value(parent)),
553 let parent_node = node.file_id.call_node(db)?;
559 /// Skips the attributed item that caused the macro invocation we are climbing up
560 pub fn ancestors_with_macros_skip_attr_item(
562 db: &dyn db::AstDatabase,
563 ) -> impl Iterator<Item = InFile<SyntaxNode>> + '_ {
564 iter::successors(Some(self), move |node| match node.value.parent() {
565 Some(parent) => Some(node.with_value(parent)),
567 let parent_node = node.file_id.call_node(db)?;
568 if node.file_id.is_attr_macro(db) {
569 // macro call was an attributed item, skip it
570 // FIXME: does this fail if this is a direct expansion of another macro?
571 parent_node.map(|node| node.parent()).transpose()
580 impl<'a> InFile<&'a SyntaxNode> {
581 /// Falls back to the macro call range if the node cannot be mapped up fully.
582 pub fn original_file_range(self, db: &dyn db::AstDatabase) -> FileRange {
583 if let Some(res) = self.original_file_range_opt(db) {
587 // Fall back to whole macro call.
588 let mut node = self.cloned();
589 while let Some(call_node) = node.file_id.call_node(db) {
593 let orig_file = node.file_id.original_file(db);
594 assert_eq!(node.file_id, orig_file.into());
596 FileRange { file_id: orig_file, range: node.value.text_range() }
599 /// Attempts to map the syntax node back up its macro calls.
600 pub fn original_file_range_opt(self, db: &dyn db::AstDatabase) -> Option<FileRange> {
601 match original_range_opt(db, self) {
603 let original_file = range.file_id.original_file(db);
604 if range.file_id != original_file.into() {
605 tracing::error!("Failed mapping up more for {:?}", range);
607 Some(FileRange { file_id: original_file, range: range.value })
609 _ if !self.file_id.is_macro() => Some(FileRange {
610 file_id: self.file_id.original_file(db),
611 range: self.value.text_range(),
618 fn original_range_opt(
619 db: &dyn db::AstDatabase,
620 node: InFile<&SyntaxNode>,
621 ) -> Option<InFile<TextRange>> {
622 let expansion = node.file_id.expansion_info(db)?;
624 // the input node has only one token ?
625 let single = skip_trivia_token(node.value.first_token()?, Direction::Next)?
626 == skip_trivia_token(node.value.last_token()?, Direction::Prev)?;
628 node.value.descendants().find_map(|it| {
629 let first = skip_trivia_token(it.first_token()?, Direction::Next)?;
630 let first = ascend_call_token(db, &expansion, node.with_value(first))?;
632 let last = skip_trivia_token(it.last_token()?, Direction::Prev)?;
633 let last = ascend_call_token(db, &expansion, node.with_value(last))?;
635 if (!single && first == last) || (first.file_id != last.file_id) {
639 Some(first.with_value(first.value.text_range().cover(last.value.text_range())))
643 fn ascend_call_token(
644 db: &dyn db::AstDatabase,
645 expansion: &ExpansionInfo,
646 token: InFile<SyntaxToken>,
647 ) -> Option<InFile<SyntaxToken>> {
648 let (mapped, origin) = expansion.map_token_up(db, token.as_ref())?;
649 if origin != Origin::Call {
652 if let Some(info) = mapped.file_id.expansion_info(db) {
653 return ascend_call_token(db, &info, mapped);
658 impl InFile<SyntaxToken> {
659 pub fn ancestors_with_macros(
661 db: &dyn db::AstDatabase,
662 ) -> impl Iterator<Item = InFile<SyntaxNode>> + '_ {
663 self.value.parent().into_iter().flat_map({
664 let file_id = self.file_id;
665 move |parent| InFile::new(file_id, parent).ancestors_with_macros(db)
670 impl<N: AstNode> InFile<N> {
671 pub fn descendants<T: AstNode>(self) -> impl Iterator<Item = InFile<T>> {
672 self.value.syntax().descendants().filter_map(T::cast).map(move |n| self.with_value(n))
675 pub fn syntax(&self) -> InFile<&SyntaxNode> {
676 self.with_value(self.value.syntax())
679 pub fn nodes_with_attributes<'db>(
681 db: &'db dyn db::AstDatabase,
682 ) -> impl Iterator<Item = InFile<N>> + 'db
686 iter::successors(Some(self), move |node| {
687 let InFile { file_id, value } = node.file_id.call_node(db)?;
688 N::cast(value).map(|n| InFile::new(file_id, n))
692 pub fn node_with_attributes(self, db: &dyn db::AstDatabase) -> InFile<N> {
693 self.nodes_with_attributes(db).last().unwrap()
697 /// In Rust, macros expand token trees to token trees. When we want to turn a
698 /// token tree into an AST node, we need to figure out what kind of AST node we
699 /// want: something like `foo` can be a type, an expression, or a pattern.
701 /// Naively, one would think that "what this expands to" is a property of a
702 /// particular macro: macro `m1` returns an item, while macro `m2` returns an
703 /// expression, etc. That's not the case -- macros are polymorphic in the
704 /// result, and can expand to any type of the AST node.
706 /// What defines the actual AST node is the syntactic context of the macro
707 /// invocation. As a contrived example, in `let T![*] = T![*];` the first `T`
708 /// expands to a pattern, while the second one expands to an expression.
710 /// `ExpandTo` captures this bit of information about a particular macro call
712 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
722 pub fn from_call_site(call: &ast::MacroCall) -> ExpandTo {
723 use syntax::SyntaxKind::*;
725 let syn = call.syntax();
727 let parent = match syn.parent() {
729 None => return ExpandTo::Statements,
732 match parent.kind() {
733 MACRO_ITEMS | SOURCE_FILE | ITEM_LIST => ExpandTo::Items,
734 MACRO_STMTS | EXPR_STMT | STMT_LIST => ExpandTo::Statements,
735 MACRO_PAT => ExpandTo::Pattern,
736 MACRO_TYPE => ExpandTo::Type,
738 ARG_LIST | TRY_EXPR | TUPLE_EXPR | PAREN_EXPR | ARRAY_EXPR | FOR_EXPR | PATH_EXPR
739 | CLOSURE_EXPR | CONDITION | BREAK_EXPR | RETURN_EXPR | MATCH_EXPR | MATCH_ARM
740 | MATCH_GUARD | RECORD_EXPR_FIELD | CALL_EXPR | INDEX_EXPR | METHOD_CALL_EXPR
741 | FIELD_EXPR | AWAIT_EXPR | CAST_EXPR | REF_EXPR | PREFIX_EXPR | RANGE_EXPR
742 | BIN_EXPR => ExpandTo::Expr,
744 // FIXME: Handle LHS Pattern
749 // Unknown , Just guess it is `Items`