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-rw-r--r--compiler/rustc_ast_lowering/src/expr.rs1914
1 files changed, 1914 insertions, 0 deletions
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
new file mode 100644
index 000000000..fb6715ff1
--- /dev/null
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -0,0 +1,1914 @@
+use super::ResolverAstLoweringExt;
+use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
+use crate::{FnDeclKind, ImplTraitPosition};
+
+use rustc_ast::attr;
+use rustc_ast::ptr::P as AstP;
+use rustc_ast::*;
+use rustc_data_structures::stack::ensure_sufficient_stack;
+use rustc_data_structures::thin_vec::ThinVec;
+use rustc_errors::struct_span_err;
+use rustc_hir as hir;
+use rustc_hir::def::Res;
+use rustc_hir::definitions::DefPathData;
+use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
+use rustc_span::symbol::{sym, Ident};
+use rustc_span::DUMMY_SP;
+
+impl<'hir> LoweringContext<'_, 'hir> {
+ fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
+ self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
+ }
+
+ pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.lower_expr_mut(e))
+ }
+
+ pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
+ ensure_sufficient_stack(|| {
+ let kind = match e.kind {
+ ExprKind::Box(ref inner) => hir::ExprKind::Box(self.lower_expr(inner)),
+ ExprKind::Array(ref exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
+ ExprKind::ConstBlock(ref anon_const) => {
+ let anon_const = self.lower_anon_const(anon_const);
+ hir::ExprKind::ConstBlock(anon_const)
+ }
+ ExprKind::Repeat(ref expr, ref count) => {
+ let expr = self.lower_expr(expr);
+ let count = self.lower_array_length(count);
+ hir::ExprKind::Repeat(expr, count)
+ }
+ ExprKind::Tup(ref elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
+ ExprKind::Call(ref f, ref args) => {
+ if e.attrs.get(0).map_or(false, |a| a.has_name(sym::rustc_box)) {
+ if let [inner] = &args[..] && e.attrs.len() == 1 {
+ let kind = hir::ExprKind::Box(self.lower_expr(&inner));
+ let hir_id = self.lower_node_id(e.id);
+ return hir::Expr { hir_id, kind, span: self.lower_span(e.span) };
+ } else {
+ self.tcx.sess
+ .struct_span_err(
+ e.span,
+ "#[rustc_box] requires precisely one argument \
+ and no other attributes are allowed",
+ )
+ .emit();
+ hir::ExprKind::Err
+ }
+ } else if let Some(legacy_args) = self.resolver.legacy_const_generic_args(f) {
+ self.lower_legacy_const_generics((**f).clone(), args.clone(), &legacy_args)
+ } else {
+ let f = self.lower_expr(f);
+ hir::ExprKind::Call(f, self.lower_exprs(args))
+ }
+ }
+ ExprKind::MethodCall(ref seg, ref args, span) => {
+ let hir_seg = self.arena.alloc(self.lower_path_segment(
+ e.span,
+ seg,
+ ParamMode::Optional,
+ ParenthesizedGenericArgs::Err,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ ));
+ let args = self.lower_exprs(args);
+ hir::ExprKind::MethodCall(hir_seg, args, self.lower_span(span))
+ }
+ ExprKind::Binary(binop, ref lhs, ref rhs) => {
+ let binop = self.lower_binop(binop);
+ let lhs = self.lower_expr(lhs);
+ let rhs = self.lower_expr(rhs);
+ hir::ExprKind::Binary(binop, lhs, rhs)
+ }
+ ExprKind::Unary(op, ref ohs) => {
+ let op = self.lower_unop(op);
+ let ohs = self.lower_expr(ohs);
+ hir::ExprKind::Unary(op, ohs)
+ }
+ ExprKind::Lit(ref l) => {
+ hir::ExprKind::Lit(respan(self.lower_span(l.span), l.kind.clone()))
+ }
+ ExprKind::Cast(ref expr, ref ty) => {
+ let expr = self.lower_expr(expr);
+ let ty =
+ self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+ hir::ExprKind::Cast(expr, ty)
+ }
+ ExprKind::Type(ref expr, ref ty) => {
+ let expr = self.lower_expr(expr);
+ let ty =
+ self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+ hir::ExprKind::Type(expr, ty)
+ }
+ ExprKind::AddrOf(k, m, ref ohs) => {
+ let ohs = self.lower_expr(ohs);
+ hir::ExprKind::AddrOf(k, m, ohs)
+ }
+ ExprKind::Let(ref pat, ref scrutinee, span) => {
+ hir::ExprKind::Let(self.arena.alloc(hir::Let {
+ hir_id: self.next_id(),
+ span: self.lower_span(span),
+ pat: self.lower_pat(pat),
+ ty: None,
+ init: self.lower_expr(scrutinee),
+ }))
+ }
+ ExprKind::If(ref cond, ref then, ref else_opt) => {
+ self.lower_expr_if(cond, then, else_opt.as_deref())
+ }
+ ExprKind::While(ref cond, ref body, opt_label) => {
+ self.with_loop_scope(e.id, |this| {
+ let span =
+ this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
+ this.lower_expr_while_in_loop_scope(span, cond, body, opt_label)
+ })
+ }
+ ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
+ hir::ExprKind::Loop(
+ this.lower_block(body, false),
+ this.lower_label(opt_label),
+ hir::LoopSource::Loop,
+ DUMMY_SP,
+ )
+ }),
+ ExprKind::TryBlock(ref body) => self.lower_expr_try_block(body),
+ ExprKind::Match(ref expr, ref arms) => hir::ExprKind::Match(
+ self.lower_expr(expr),
+ self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
+ hir::MatchSource::Normal,
+ ),
+ ExprKind::Async(capture_clause, closure_node_id, ref block) => self
+ .make_async_expr(
+ capture_clause,
+ closure_node_id,
+ None,
+ block.span,
+ hir::AsyncGeneratorKind::Block,
+ |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
+ ),
+ ExprKind::Await(ref expr) => {
+ let span = if expr.span.hi() < e.span.hi() {
+ expr.span.shrink_to_hi().with_hi(e.span.hi())
+ } else {
+ // this is a recovered `await expr`
+ e.span
+ };
+ self.lower_expr_await(span, expr)
+ }
+ ExprKind::Closure(
+ ref binder,
+ capture_clause,
+ asyncness,
+ movability,
+ ref decl,
+ ref body,
+ fn_decl_span,
+ ) => {
+ if let Async::Yes { closure_id, .. } = asyncness {
+ self.lower_expr_async_closure(
+ binder,
+ capture_clause,
+ e.id,
+ closure_id,
+ decl,
+ body,
+ fn_decl_span,
+ )
+ } else {
+ self.lower_expr_closure(
+ binder,
+ capture_clause,
+ e.id,
+ movability,
+ decl,
+ body,
+ fn_decl_span,
+ )
+ }
+ }
+ ExprKind::Block(ref blk, opt_label) => {
+ let opt_label = self.lower_label(opt_label);
+ hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
+ }
+ ExprKind::Assign(ref el, ref er, span) => {
+ self.lower_expr_assign(el, er, span, e.span)
+ }
+ ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
+ self.lower_binop(op),
+ self.lower_expr(el),
+ self.lower_expr(er),
+ ),
+ ExprKind::Field(ref el, ident) => {
+ hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(ident))
+ }
+ ExprKind::Index(ref el, ref er) => {
+ hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er))
+ }
+ ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
+ self.lower_expr_range_closed(e.span, e1, e2)
+ }
+ ExprKind::Range(ref e1, ref e2, lims) => {
+ self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), lims)
+ }
+ ExprKind::Underscore => {
+ self.tcx
+ .sess.struct_span_err(
+ e.span,
+ "in expressions, `_` can only be used on the left-hand side of an assignment",
+ )
+ .span_label(e.span, "`_` not allowed here")
+ .emit();
+ hir::ExprKind::Err
+ }
+ ExprKind::Path(ref qself, ref path) => {
+ let qpath = self.lower_qpath(
+ e.id,
+ qself,
+ path,
+ ParamMode::Optional,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ );
+ hir::ExprKind::Path(qpath)
+ }
+ ExprKind::Break(opt_label, ref opt_expr) => {
+ let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
+ hir::ExprKind::Break(self.lower_jump_destination(e.id, opt_label), opt_expr)
+ }
+ ExprKind::Continue(opt_label) => {
+ hir::ExprKind::Continue(self.lower_jump_destination(e.id, opt_label))
+ }
+ ExprKind::Ret(ref e) => {
+ let e = e.as_ref().map(|x| self.lower_expr(x));
+ hir::ExprKind::Ret(e)
+ }
+ ExprKind::Yeet(ref sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
+ ExprKind::InlineAsm(ref asm) => {
+ hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
+ }
+ ExprKind::Struct(ref se) => {
+ let rest = match &se.rest {
+ StructRest::Base(e) => Some(self.lower_expr(e)),
+ StructRest::Rest(sp) => {
+ self.tcx
+ .sess
+ .struct_span_err(*sp, "base expression required after `..`")
+ .span_label(*sp, "add a base expression here")
+ .emit();
+ Some(&*self.arena.alloc(self.expr_err(*sp)))
+ }
+ StructRest::None => None,
+ };
+ hir::ExprKind::Struct(
+ self.arena.alloc(self.lower_qpath(
+ e.id,
+ &se.qself,
+ &se.path,
+ ParamMode::Optional,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ )),
+ self.arena
+ .alloc_from_iter(se.fields.iter().map(|x| self.lower_expr_field(x))),
+ rest,
+ )
+ }
+ ExprKind::Yield(ref opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
+ ExprKind::Err => hir::ExprKind::Err,
+ ExprKind::Try(ref sub_expr) => self.lower_expr_try(e.span, sub_expr),
+ ExprKind::Paren(ref ex) => {
+ let mut ex = self.lower_expr_mut(ex);
+ // Include parens in span, but only if it is a super-span.
+ if e.span.contains(ex.span) {
+ ex.span = self.lower_span(e.span);
+ }
+ // Merge attributes into the inner expression.
+ if !e.attrs.is_empty() {
+ let old_attrs =
+ self.attrs.get(&ex.hir_id.local_id).map(|la| *la).unwrap_or(&[]);
+ self.attrs.insert(
+ ex.hir_id.local_id,
+ &*self.arena.alloc_from_iter(
+ e.attrs
+ .iter()
+ .map(|a| self.lower_attr(a))
+ .chain(old_attrs.iter().cloned()),
+ ),
+ );
+ }
+ return ex;
+ }
+
+ // Desugar `ExprForLoop`
+ // from: `[opt_ident]: for <pat> in <head> <body>`
+ ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
+ return self.lower_expr_for(e, pat, head, body, opt_label);
+ }
+ ExprKind::MacCall(_) => panic!("{:?} shouldn't exist here", e.span),
+ };
+
+ let hir_id = self.lower_node_id(e.id);
+ self.lower_attrs(hir_id, &e.attrs);
+ hir::Expr { hir_id, kind, span: self.lower_span(e.span) }
+ })
+ }
+
+ fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
+ match u {
+ UnOp::Deref => hir::UnOp::Deref,
+ UnOp::Not => hir::UnOp::Not,
+ UnOp::Neg => hir::UnOp::Neg,
+ }
+ }
+
+ fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
+ Spanned {
+ node: match b.node {
+ BinOpKind::Add => hir::BinOpKind::Add,
+ BinOpKind::Sub => hir::BinOpKind::Sub,
+ BinOpKind::Mul => hir::BinOpKind::Mul,
+ BinOpKind::Div => hir::BinOpKind::Div,
+ BinOpKind::Rem => hir::BinOpKind::Rem,
+ BinOpKind::And => hir::BinOpKind::And,
+ BinOpKind::Or => hir::BinOpKind::Or,
+ BinOpKind::BitXor => hir::BinOpKind::BitXor,
+ BinOpKind::BitAnd => hir::BinOpKind::BitAnd,
+ BinOpKind::BitOr => hir::BinOpKind::BitOr,
+ BinOpKind::Shl => hir::BinOpKind::Shl,
+ BinOpKind::Shr => hir::BinOpKind::Shr,
+ BinOpKind::Eq => hir::BinOpKind::Eq,
+ BinOpKind::Lt => hir::BinOpKind::Lt,
+ BinOpKind::Le => hir::BinOpKind::Le,
+ BinOpKind::Ne => hir::BinOpKind::Ne,
+ BinOpKind::Ge => hir::BinOpKind::Ge,
+ BinOpKind::Gt => hir::BinOpKind::Gt,
+ },
+ span: self.lower_span(b.span),
+ }
+ }
+
+ fn lower_legacy_const_generics(
+ &mut self,
+ mut f: Expr,
+ args: Vec<AstP<Expr>>,
+ legacy_args_idx: &[usize],
+ ) -> hir::ExprKind<'hir> {
+ let ExprKind::Path(None, ref mut path) = f.kind else {
+ unreachable!();
+ };
+
+ // Split the arguments into const generics and normal arguments
+ let mut real_args = vec![];
+ let mut generic_args = vec![];
+ for (idx, arg) in args.into_iter().enumerate() {
+ if legacy_args_idx.contains(&idx) {
+ let parent_def_id = self.current_hir_id_owner;
+ let node_id = self.next_node_id();
+
+ // Add a definition for the in-band const def.
+ self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
+
+ let anon_const = AnonConst { id: node_id, value: arg };
+ generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
+ } else {
+ real_args.push(arg);
+ }
+ }
+
+ // Add generic args to the last element of the path.
+ let last_segment = path.segments.last_mut().unwrap();
+ assert!(last_segment.args.is_none());
+ last_segment.args = Some(AstP(GenericArgs::AngleBracketed(AngleBracketedArgs {
+ span: DUMMY_SP,
+ args: generic_args,
+ })));
+
+ // Now lower everything as normal.
+ let f = self.lower_expr(&f);
+ hir::ExprKind::Call(f, self.lower_exprs(&real_args))
+ }
+
+ fn lower_expr_if(
+ &mut self,
+ cond: &Expr,
+ then: &Block,
+ else_opt: Option<&Expr>,
+ ) -> hir::ExprKind<'hir> {
+ let lowered_cond = self.lower_expr(cond);
+ let new_cond = self.manage_let_cond(lowered_cond);
+ let then_expr = self.lower_block_expr(then);
+ if let Some(rslt) = else_opt {
+ hir::ExprKind::If(new_cond, self.arena.alloc(then_expr), Some(self.lower_expr(rslt)))
+ } else {
+ hir::ExprKind::If(new_cond, self.arena.alloc(then_expr), None)
+ }
+ }
+
+ // If `cond` kind is `let`, returns `let`. Otherwise, wraps and returns `cond`
+ // in a temporary block.
+ fn manage_let_cond(&mut self, cond: &'hir hir::Expr<'hir>) -> &'hir hir::Expr<'hir> {
+ fn has_let_expr<'hir>(expr: &'hir hir::Expr<'hir>) -> bool {
+ match expr.kind {
+ hir::ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
+ hir::ExprKind::Let(..) => true,
+ _ => false,
+ }
+ }
+ if has_let_expr(cond) {
+ cond
+ } else {
+ let reason = DesugaringKind::CondTemporary;
+ let span_block = self.mark_span_with_reason(reason, cond.span, None);
+ self.expr_drop_temps(span_block, cond, AttrVec::new())
+ }
+ }
+
+ // We desugar: `'label: while $cond $body` into:
+ //
+ // ```
+ // 'label: loop {
+ // if { let _t = $cond; _t } {
+ // $body
+ // }
+ // else {
+ // break;
+ // }
+ // }
+ // ```
+ //
+ // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
+ // to preserve drop semantics since `while $cond { ... }` does not
+ // let temporaries live outside of `cond`.
+ fn lower_expr_while_in_loop_scope(
+ &mut self,
+ span: Span,
+ cond: &Expr,
+ body: &Block,
+ opt_label: Option<Label>,
+ ) -> hir::ExprKind<'hir> {
+ let lowered_cond = self.with_loop_condition_scope(|t| t.lower_expr(cond));
+ let new_cond = self.manage_let_cond(lowered_cond);
+ let then = self.lower_block_expr(body);
+ let expr_break = self.expr_break(span, ThinVec::new());
+ let stmt_break = self.stmt_expr(span, expr_break);
+ let else_blk = self.block_all(span, arena_vec![self; stmt_break], None);
+ let else_expr = self.arena.alloc(self.expr_block(else_blk, ThinVec::new()));
+ let if_kind = hir::ExprKind::If(new_cond, self.arena.alloc(then), Some(else_expr));
+ let if_expr = self.expr(span, if_kind, ThinVec::new());
+ let block = self.block_expr(self.arena.alloc(if_expr));
+ let span = self.lower_span(span.with_hi(cond.span.hi()));
+ let opt_label = self.lower_label(opt_label);
+ hir::ExprKind::Loop(block, opt_label, hir::LoopSource::While, span)
+ }
+
+ /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_output(<expr>) }`,
+ /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_output(()) }`
+ /// and save the block id to use it as a break target for desugaring of the `?` operator.
+ fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
+ self.with_catch_scope(body.id, |this| {
+ let mut block = this.lower_block_noalloc(body, true);
+
+ // Final expression of the block (if present) or `()` with span at the end of block
+ let (try_span, tail_expr) = if let Some(expr) = block.expr.take() {
+ (
+ this.mark_span_with_reason(
+ DesugaringKind::TryBlock,
+ expr.span,
+ this.allow_try_trait.clone(),
+ ),
+ expr,
+ )
+ } else {
+ let try_span = this.mark_span_with_reason(
+ DesugaringKind::TryBlock,
+ this.tcx.sess.source_map().end_point(body.span),
+ this.allow_try_trait.clone(),
+ );
+
+ (try_span, this.expr_unit(try_span))
+ };
+
+ let ok_wrapped_span =
+ this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
+
+ // `::std::ops::Try::from_output($tail_expr)`
+ block.expr = Some(this.wrap_in_try_constructor(
+ hir::LangItem::TryTraitFromOutput,
+ try_span,
+ tail_expr,
+ ok_wrapped_span,
+ ));
+
+ hir::ExprKind::Block(this.arena.alloc(block), None)
+ })
+ }
+
+ fn wrap_in_try_constructor(
+ &mut self,
+ lang_item: hir::LangItem,
+ method_span: Span,
+ expr: &'hir hir::Expr<'hir>,
+ overall_span: Span,
+ ) -> &'hir hir::Expr<'hir> {
+ let constructor = self.arena.alloc(self.expr_lang_item_path(
+ method_span,
+ lang_item,
+ ThinVec::new(),
+ None,
+ ));
+ self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
+ }
+
+ fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
+ let pat = self.lower_pat(&arm.pat);
+ let guard = arm.guard.as_ref().map(|cond| {
+ if let ExprKind::Let(ref pat, ref scrutinee, span) = cond.kind {
+ hir::Guard::IfLet(self.arena.alloc(hir::Let {
+ hir_id: self.next_id(),
+ span: self.lower_span(span),
+ pat: self.lower_pat(pat),
+ ty: None,
+ init: self.lower_expr(scrutinee),
+ }))
+ } else {
+ hir::Guard::If(self.lower_expr(cond))
+ }
+ });
+ let hir_id = self.next_id();
+ self.lower_attrs(hir_id, &arm.attrs);
+ hir::Arm {
+ hir_id,
+ pat,
+ guard,
+ body: self.lower_expr(&arm.body),
+ span: self.lower_span(arm.span),
+ }
+ }
+
+ /// Lower an `async` construct to a generator that is then wrapped so it implements `Future`.
+ ///
+ /// This results in:
+ ///
+ /// ```text
+ /// std::future::from_generator(static move? |_task_context| -> <ret_ty> {
+ /// <body>
+ /// })
+ /// ```
+ pub(super) fn make_async_expr(
+ &mut self,
+ capture_clause: CaptureBy,
+ closure_node_id: NodeId,
+ ret_ty: Option<AstP<Ty>>,
+ span: Span,
+ async_gen_kind: hir::AsyncGeneratorKind,
+ body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
+ ) -> hir::ExprKind<'hir> {
+ let output = match ret_ty {
+ Some(ty) => hir::FnRetTy::Return(
+ self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::AsyncBlock)),
+ ),
+ None => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
+ };
+
+ // Resume argument type. We let the compiler infer this to simplify the lowering. It is
+ // fully constrained by `future::from_generator`.
+ let input_ty = hir::Ty {
+ hir_id: self.next_id(),
+ kind: hir::TyKind::Infer,
+ span: self.lower_span(span),
+ };
+
+ // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
+ let fn_decl = self.arena.alloc(hir::FnDecl {
+ inputs: arena_vec![self; input_ty],
+ output,
+ c_variadic: false,
+ implicit_self: hir::ImplicitSelfKind::None,
+ });
+
+ // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
+ let (pat, task_context_hid) = self.pat_ident_binding_mode(
+ span,
+ Ident::with_dummy_span(sym::_task_context),
+ hir::BindingAnnotation::Mutable,
+ );
+ let param = hir::Param {
+ hir_id: self.next_id(),
+ pat,
+ ty_span: self.lower_span(span),
+ span: self.lower_span(span),
+ };
+ let params = arena_vec![self; param];
+
+ let body = self.lower_body(move |this| {
+ this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
+
+ let old_ctx = this.task_context;
+ this.task_context = Some(task_context_hid);
+ let res = body(this);
+ this.task_context = old_ctx;
+ (params, res)
+ });
+
+ // `static |_task_context| -> <ret_ty> { body }`:
+ let generator_kind = {
+ let c = self.arena.alloc(hir::Closure {
+ binder: hir::ClosureBinder::Default,
+ capture_clause,
+ bound_generic_params: &[],
+ fn_decl,
+ body,
+ fn_decl_span: self.lower_span(span),
+ movability: Some(hir::Movability::Static),
+ });
+
+ hir::ExprKind::Closure(c)
+ };
+ let generator = hir::Expr {
+ hir_id: self.lower_node_id(closure_node_id),
+ kind: generator_kind,
+ span: self.lower_span(span),
+ };
+
+ // `future::from_generator`:
+ let unstable_span =
+ self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
+ let gen_future = self.expr_lang_item_path(
+ unstable_span,
+ hir::LangItem::FromGenerator,
+ ThinVec::new(),
+ None,
+ );
+
+ // `future::from_generator(generator)`:
+ hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
+ }
+
+ /// Desugar `<expr>.await` into:
+ /// ```ignore (pseudo-rust)
+ /// match ::std::future::IntoFuture::into_future(<expr>) {
+ /// mut __awaitee => loop {
+ /// match unsafe { ::std::future::Future::poll(
+ /// <::std::pin::Pin>::new_unchecked(&mut __awaitee),
+ /// ::std::future::get_context(task_context),
+ /// ) } {
+ /// ::std::task::Poll::Ready(result) => break result,
+ /// ::std::task::Poll::Pending => {}
+ /// }
+ /// task_context = yield ();
+ /// }
+ /// }
+ /// ```
+ fn lower_expr_await(&mut self, dot_await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
+ let full_span = expr.span.to(dot_await_span);
+ match self.generator_kind {
+ Some(hir::GeneratorKind::Async(_)) => {}
+ Some(hir::GeneratorKind::Gen) | None => {
+ let mut err = struct_span_err!(
+ self.tcx.sess,
+ dot_await_span,
+ E0728,
+ "`await` is only allowed inside `async` functions and blocks"
+ );
+ err.span_label(dot_await_span, "only allowed inside `async` functions and blocks");
+ if let Some(item_sp) = self.current_item {
+ err.span_label(item_sp, "this is not `async`");
+ }
+ err.emit();
+ }
+ }
+ let span = self.mark_span_with_reason(DesugaringKind::Await, dot_await_span, None);
+ let gen_future_span = self.mark_span_with_reason(
+ DesugaringKind::Await,
+ full_span,
+ self.allow_gen_future.clone(),
+ );
+ let expr = self.lower_expr_mut(expr);
+ let expr_hir_id = expr.hir_id;
+
+ // Note that the name of this binding must not be changed to something else because
+ // debuggers and debugger extensions expect it to be called `__awaitee`. They use
+ // this name to identify what is being awaited by a suspended async functions.
+ let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
+ let (awaitee_pat, awaitee_pat_hid) =
+ self.pat_ident_binding_mode(span, awaitee_ident, hir::BindingAnnotation::Mutable);
+
+ let task_context_ident = Ident::with_dummy_span(sym::_task_context);
+
+ // unsafe {
+ // ::std::future::Future::poll(
+ // ::std::pin::Pin::new_unchecked(&mut __awaitee),
+ // ::std::future::get_context(task_context),
+ // )
+ // }
+ let poll_expr = {
+ let awaitee = self.expr_ident(span, awaitee_ident, awaitee_pat_hid);
+ let ref_mut_awaitee = self.expr_mut_addr_of(span, awaitee);
+ let task_context = if let Some(task_context_hid) = self.task_context {
+ self.expr_ident_mut(span, task_context_ident, task_context_hid)
+ } else {
+ // Use of `await` outside of an async context, we cannot use `task_context` here.
+ self.expr_err(span)
+ };
+ let new_unchecked = self.expr_call_lang_item_fn_mut(
+ span,
+ hir::LangItem::PinNewUnchecked,
+ arena_vec![self; ref_mut_awaitee],
+ Some(expr_hir_id),
+ );
+ let get_context = self.expr_call_lang_item_fn_mut(
+ gen_future_span,
+ hir::LangItem::GetContext,
+ arena_vec![self; task_context],
+ Some(expr_hir_id),
+ );
+ let call = self.expr_call_lang_item_fn(
+ span,
+ hir::LangItem::FuturePoll,
+ arena_vec![self; new_unchecked, get_context],
+ Some(expr_hir_id),
+ );
+ self.arena.alloc(self.expr_unsafe(call))
+ };
+
+ // `::std::task::Poll::Ready(result) => break result`
+ let loop_node_id = self.next_node_id();
+ let loop_hir_id = self.lower_node_id(loop_node_id);
+ let ready_arm = {
+ let x_ident = Ident::with_dummy_span(sym::result);
+ let (x_pat, x_pat_hid) = self.pat_ident(gen_future_span, x_ident);
+ let x_expr = self.expr_ident(gen_future_span, x_ident, x_pat_hid);
+ let ready_field = self.single_pat_field(gen_future_span, x_pat);
+ let ready_pat = self.pat_lang_item_variant(
+ span,
+ hir::LangItem::PollReady,
+ ready_field,
+ Some(expr_hir_id),
+ );
+ let break_x = self.with_loop_scope(loop_node_id, move |this| {
+ let expr_break =
+ hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
+ this.arena.alloc(this.expr(gen_future_span, expr_break, ThinVec::new()))
+ });
+ self.arm(ready_pat, break_x)
+ };
+
+ // `::std::task::Poll::Pending => {}`
+ let pending_arm = {
+ let pending_pat = self.pat_lang_item_variant(
+ span,
+ hir::LangItem::PollPending,
+ &[],
+ Some(expr_hir_id),
+ );
+ let empty_block = self.expr_block_empty(span);
+ self.arm(pending_pat, empty_block)
+ };
+
+ let inner_match_stmt = {
+ let match_expr = self.expr_match(
+ span,
+ poll_expr,
+ arena_vec![self; ready_arm, pending_arm],
+ hir::MatchSource::AwaitDesugar,
+ );
+ self.stmt_expr(span, match_expr)
+ };
+
+ // task_context = yield ();
+ let yield_stmt = {
+ let unit = self.expr_unit(span);
+ let yield_expr = self.expr(
+ span,
+ hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
+ ThinVec::new(),
+ );
+ let yield_expr = self.arena.alloc(yield_expr);
+
+ if let Some(task_context_hid) = self.task_context {
+ let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
+ let assign = self.expr(
+ span,
+ hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)),
+ AttrVec::new(),
+ );
+ self.stmt_expr(span, assign)
+ } else {
+ // Use of `await` outside of an async context. Return `yield_expr` so that we can
+ // proceed with type checking.
+ self.stmt(span, hir::StmtKind::Semi(yield_expr))
+ }
+ };
+
+ let loop_block = self.block_all(span, arena_vec![self; inner_match_stmt, yield_stmt], None);
+
+ // loop { .. }
+ let loop_expr = self.arena.alloc(hir::Expr {
+ hir_id: loop_hir_id,
+ kind: hir::ExprKind::Loop(
+ loop_block,
+ None,
+ hir::LoopSource::Loop,
+ self.lower_span(span),
+ ),
+ span: self.lower_span(span),
+ });
+
+ // mut __awaitee => loop { ... }
+ let awaitee_arm = self.arm(awaitee_pat, loop_expr);
+
+ // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
+ let into_future_span = self.mark_span_with_reason(
+ DesugaringKind::Await,
+ dot_await_span,
+ self.allow_into_future.clone(),
+ );
+ let into_future_expr = self.expr_call_lang_item_fn(
+ into_future_span,
+ hir::LangItem::IntoFutureIntoFuture,
+ arena_vec![self; expr],
+ Some(expr_hir_id),
+ );
+
+ // match <into_future_expr> {
+ // mut __awaitee => loop { .. }
+ // }
+ hir::ExprKind::Match(
+ into_future_expr,
+ arena_vec![self; awaitee_arm],
+ hir::MatchSource::AwaitDesugar,
+ )
+ }
+
+ fn lower_expr_closure(
+ &mut self,
+ binder: &ClosureBinder,
+ capture_clause: CaptureBy,
+ closure_id: NodeId,
+ movability: Movability,
+ decl: &FnDecl,
+ body: &Expr,
+ fn_decl_span: Span,
+ ) -> hir::ExprKind<'hir> {
+ let (binder_clause, generic_params) = self.lower_closure_binder(binder);
+
+ let (body_id, generator_option) = self.with_new_scopes(move |this| {
+ let prev = this.current_item;
+ this.current_item = Some(fn_decl_span);
+ let mut generator_kind = None;
+ let body_id = this.lower_fn_body(decl, |this| {
+ let e = this.lower_expr_mut(body);
+ generator_kind = this.generator_kind;
+ e
+ });
+ let generator_option =
+ this.generator_movability_for_fn(&decl, fn_decl_span, generator_kind, movability);
+ this.current_item = prev;
+ (body_id, generator_option)
+ });
+
+ let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
+ // Lower outside new scope to preserve `is_in_loop_condition`.
+ let fn_decl = self.lower_fn_decl(decl, None, FnDeclKind::Closure, None);
+
+ let c = self.arena.alloc(hir::Closure {
+ binder: binder_clause,
+ capture_clause,
+ bound_generic_params,
+ fn_decl,
+ body: body_id,
+ fn_decl_span: self.lower_span(fn_decl_span),
+ movability: generator_option,
+ });
+
+ hir::ExprKind::Closure(c)
+ }
+
+ fn generator_movability_for_fn(
+ &mut self,
+ decl: &FnDecl,
+ fn_decl_span: Span,
+ generator_kind: Option<hir::GeneratorKind>,
+ movability: Movability,
+ ) -> Option<hir::Movability> {
+ match generator_kind {
+ Some(hir::GeneratorKind::Gen) => {
+ if decl.inputs.len() > 1 {
+ struct_span_err!(
+ self.tcx.sess,
+ fn_decl_span,
+ E0628,
+ "too many parameters for a generator (expected 0 or 1 parameters)"
+ )
+ .emit();
+ }
+ Some(movability)
+ }
+ Some(hir::GeneratorKind::Async(_)) => {
+ panic!("non-`async` closure body turned `async` during lowering");
+ }
+ None => {
+ if movability == Movability::Static {
+ struct_span_err!(
+ self.tcx.sess,
+ fn_decl_span,
+ E0697,
+ "closures cannot be static"
+ )
+ .emit();
+ }
+ None
+ }
+ }
+ }
+
+ fn lower_closure_binder<'c>(
+ &mut self,
+ binder: &'c ClosureBinder,
+ ) -> (hir::ClosureBinder, &'c [GenericParam]) {
+ let (binder, params) = match binder {
+ ClosureBinder::NotPresent => (hir::ClosureBinder::Default, &[][..]),
+ &ClosureBinder::For { span, ref generic_params } => {
+ let span = self.lower_span(span);
+ (hir::ClosureBinder::For { span }, &**generic_params)
+ }
+ };
+
+ (binder, params)
+ }
+
+ fn lower_expr_async_closure(
+ &mut self,
+ binder: &ClosureBinder,
+ capture_clause: CaptureBy,
+ closure_id: NodeId,
+ inner_closure_id: NodeId,
+ decl: &FnDecl,
+ body: &Expr,
+ fn_decl_span: Span,
+ ) -> hir::ExprKind<'hir> {
+ if let &ClosureBinder::For { span, .. } = binder {
+ self.tcx.sess.span_err(
+ span,
+ "`for<...>` binders on `async` closures are not currently supported",
+ );
+ }
+
+ let (binder_clause, generic_params) = self.lower_closure_binder(binder);
+
+ let outer_decl =
+ FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
+
+ let body = self.with_new_scopes(|this| {
+ // FIXME(cramertj): allow `async` non-`move` closures with arguments.
+ if capture_clause == CaptureBy::Ref && !decl.inputs.is_empty() {
+ struct_span_err!(
+ this.tcx.sess,
+ fn_decl_span,
+ E0708,
+ "`async` non-`move` closures with parameters are not currently supported",
+ )
+ .help(
+ "consider using `let` statements to manually capture \
+ variables by reference before entering an `async move` closure",
+ )
+ .emit();
+ }
+
+ // Transform `async |x: u8| -> X { ... }` into
+ // `|x: u8| future_from_generator(|| -> X { ... })`.
+ let body_id = this.lower_fn_body(&outer_decl, |this| {
+ let async_ret_ty =
+ if let FnRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
+ let async_body = this.make_async_expr(
+ capture_clause,
+ inner_closure_id,
+ async_ret_ty,
+ body.span,
+ hir::AsyncGeneratorKind::Closure,
+ |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
+ );
+ this.expr(fn_decl_span, async_body, ThinVec::new())
+ });
+ body_id
+ });
+
+ let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
+
+ // We need to lower the declaration outside the new scope, because we
+ // have to conserve the state of being inside a loop condition for the
+ // closure argument types.
+ let fn_decl = self.lower_fn_decl(&outer_decl, None, FnDeclKind::Closure, None);
+
+ let c = self.arena.alloc(hir::Closure {
+ binder: binder_clause,
+ capture_clause,
+ bound_generic_params,
+ fn_decl,
+ body,
+ fn_decl_span: self.lower_span(fn_decl_span),
+ movability: None,
+ });
+ hir::ExprKind::Closure(c)
+ }
+
+ /// Destructure the LHS of complex assignments.
+ /// For instance, lower `(a, b) = t` to `{ let (lhs1, lhs2) = t; a = lhs1; b = lhs2; }`.
+ fn lower_expr_assign(
+ &mut self,
+ lhs: &Expr,
+ rhs: &Expr,
+ eq_sign_span: Span,
+ whole_span: Span,
+ ) -> hir::ExprKind<'hir> {
+ // Return early in case of an ordinary assignment.
+ fn is_ordinary(lower_ctx: &mut LoweringContext<'_, '_>, lhs: &Expr) -> bool {
+ match &lhs.kind {
+ ExprKind::Array(..)
+ | ExprKind::Struct(..)
+ | ExprKind::Tup(..)
+ | ExprKind::Underscore => false,
+ // Check for tuple struct constructor.
+ ExprKind::Call(callee, ..) => lower_ctx.extract_tuple_struct_path(callee).is_none(),
+ ExprKind::Paren(e) => {
+ match e.kind {
+ // We special-case `(..)` for consistency with patterns.
+ ExprKind::Range(None, None, RangeLimits::HalfOpen) => false,
+ _ => is_ordinary(lower_ctx, e),
+ }
+ }
+ _ => true,
+ }
+ }
+ if is_ordinary(self, lhs) {
+ return hir::ExprKind::Assign(
+ self.lower_expr(lhs),
+ self.lower_expr(rhs),
+ self.lower_span(eq_sign_span),
+ );
+ }
+
+ let mut assignments = vec![];
+
+ // The LHS becomes a pattern: `(lhs1, lhs2)`.
+ let pat = self.destructure_assign(lhs, eq_sign_span, &mut assignments);
+ let rhs = self.lower_expr(rhs);
+
+ // Introduce a `let` for destructuring: `let (lhs1, lhs2) = t`.
+ let destructure_let = self.stmt_let_pat(
+ None,
+ whole_span,
+ Some(rhs),
+ pat,
+ hir::LocalSource::AssignDesugar(self.lower_span(eq_sign_span)),
+ );
+
+ // `a = lhs1; b = lhs2;`.
+ let stmts = self
+ .arena
+ .alloc_from_iter(std::iter::once(destructure_let).chain(assignments.into_iter()));
+
+ // Wrap everything in a block.
+ hir::ExprKind::Block(&self.block_all(whole_span, stmts, None), None)
+ }
+
+ /// If the given expression is a path to a tuple struct, returns that path.
+ /// It is not a complete check, but just tries to reject most paths early
+ /// if they are not tuple structs.
+ /// Type checking will take care of the full validation later.
+ fn extract_tuple_struct_path<'a>(
+ &mut self,
+ expr: &'a Expr,
+ ) -> Option<(&'a Option<QSelf>, &'a Path)> {
+ if let ExprKind::Path(qself, path) = &expr.kind {
+ // Does the path resolve to something disallowed in a tuple struct/variant pattern?
+ if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
+ if partial_res.unresolved_segments() == 0
+ && !partial_res.base_res().expected_in_tuple_struct_pat()
+ {
+ return None;
+ }
+ }
+ return Some((qself, path));
+ }
+ None
+ }
+
+ /// If the given expression is a path to a unit struct, returns that path.
+ /// It is not a complete check, but just tries to reject most paths early
+ /// if they are not unit structs.
+ /// Type checking will take care of the full validation later.
+ fn extract_unit_struct_path<'a>(
+ &mut self,
+ expr: &'a Expr,
+ ) -> Option<(&'a Option<QSelf>, &'a Path)> {
+ if let ExprKind::Path(qself, path) = &expr.kind {
+ // Does the path resolve to something disallowed in a unit struct/variant pattern?
+ if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
+ if partial_res.unresolved_segments() == 0
+ && !partial_res.base_res().expected_in_unit_struct_pat()
+ {
+ return None;
+ }
+ }
+ return Some((qself, path));
+ }
+ None
+ }
+
+ /// Convert the LHS of a destructuring assignment to a pattern.
+ /// Each sub-assignment is recorded in `assignments`.
+ fn destructure_assign(
+ &mut self,
+ lhs: &Expr,
+ eq_sign_span: Span,
+ assignments: &mut Vec<hir::Stmt<'hir>>,
+ ) -> &'hir hir::Pat<'hir> {
+ self.arena.alloc(self.destructure_assign_mut(lhs, eq_sign_span, assignments))
+ }
+
+ fn destructure_assign_mut(
+ &mut self,
+ lhs: &Expr,
+ eq_sign_span: Span,
+ assignments: &mut Vec<hir::Stmt<'hir>>,
+ ) -> hir::Pat<'hir> {
+ match &lhs.kind {
+ // Underscore pattern.
+ ExprKind::Underscore => {
+ return self.pat_without_dbm(lhs.span, hir::PatKind::Wild);
+ }
+ // Slice patterns.
+ ExprKind::Array(elements) => {
+ let (pats, rest) =
+ self.destructure_sequence(elements, "slice", eq_sign_span, assignments);
+ let slice_pat = if let Some((i, span)) = rest {
+ let (before, after) = pats.split_at(i);
+ hir::PatKind::Slice(
+ before,
+ Some(self.arena.alloc(self.pat_without_dbm(span, hir::PatKind::Wild))),
+ after,
+ )
+ } else {
+ hir::PatKind::Slice(pats, None, &[])
+ };
+ return self.pat_without_dbm(lhs.span, slice_pat);
+ }
+ // Tuple structs.
+ ExprKind::Call(callee, args) => {
+ if let Some((qself, path)) = self.extract_tuple_struct_path(callee) {
+ let (pats, rest) = self.destructure_sequence(
+ args,
+ "tuple struct or variant",
+ eq_sign_span,
+ assignments,
+ );
+ let qpath = self.lower_qpath(
+ callee.id,
+ qself,
+ path,
+ ParamMode::Optional,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ );
+ // Destructure like a tuple struct.
+ let tuple_struct_pat =
+ hir::PatKind::TupleStruct(qpath, pats, rest.map(|r| r.0));
+ return self.pat_without_dbm(lhs.span, tuple_struct_pat);
+ }
+ }
+ // Unit structs and enum variants.
+ ExprKind::Path(..) => {
+ if let Some((qself, path)) = self.extract_unit_struct_path(lhs) {
+ let qpath = self.lower_qpath(
+ lhs.id,
+ qself,
+ path,
+ ParamMode::Optional,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ );
+ // Destructure like a unit struct.
+ let unit_struct_pat = hir::PatKind::Path(qpath);
+ return self.pat_without_dbm(lhs.span, unit_struct_pat);
+ }
+ }
+ // Structs.
+ ExprKind::Struct(se) => {
+ let field_pats = self.arena.alloc_from_iter(se.fields.iter().map(|f| {
+ let pat = self.destructure_assign(&f.expr, eq_sign_span, assignments);
+ hir::PatField {
+ hir_id: self.next_id(),
+ ident: self.lower_ident(f.ident),
+ pat,
+ is_shorthand: f.is_shorthand,
+ span: self.lower_span(f.span),
+ }
+ }));
+ let qpath = self.lower_qpath(
+ lhs.id,
+ &se.qself,
+ &se.path,
+ ParamMode::Optional,
+ ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+ );
+ let fields_omitted = match &se.rest {
+ StructRest::Base(e) => {
+ self.tcx
+ .sess
+ .struct_span_err(
+ e.span,
+ "functional record updates are not allowed in destructuring \
+ assignments",
+ )
+ .span_suggestion(
+ e.span,
+ "consider removing the trailing pattern",
+ "",
+ rustc_errors::Applicability::MachineApplicable,
+ )
+ .emit();
+ true
+ }
+ StructRest::Rest(_) => true,
+ StructRest::None => false,
+ };
+ let struct_pat = hir::PatKind::Struct(qpath, field_pats, fields_omitted);
+ return self.pat_without_dbm(lhs.span, struct_pat);
+ }
+ // Tuples.
+ ExprKind::Tup(elements) => {
+ let (pats, rest) =
+ self.destructure_sequence(elements, "tuple", eq_sign_span, assignments);
+ let tuple_pat = hir::PatKind::Tuple(pats, rest.map(|r| r.0));
+ return self.pat_without_dbm(lhs.span, tuple_pat);
+ }
+ ExprKind::Paren(e) => {
+ // We special-case `(..)` for consistency with patterns.
+ if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+ let tuple_pat = hir::PatKind::Tuple(&[], Some(0));
+ return self.pat_without_dbm(lhs.span, tuple_pat);
+ } else {
+ return self.destructure_assign_mut(e, eq_sign_span, assignments);
+ }
+ }
+ _ => {}
+ }
+ // Treat all other cases as normal lvalue.
+ let ident = Ident::new(sym::lhs, self.lower_span(lhs.span));
+ let (pat, binding) = self.pat_ident_mut(lhs.span, ident);
+ let ident = self.expr_ident(lhs.span, ident, binding);
+ let assign =
+ hir::ExprKind::Assign(self.lower_expr(lhs), ident, self.lower_span(eq_sign_span));
+ let expr = self.expr(lhs.span, assign, ThinVec::new());
+ assignments.push(self.stmt_expr(lhs.span, expr));
+ pat
+ }
+
+ /// Destructure a sequence of expressions occurring on the LHS of an assignment.
+ /// Such a sequence occurs in a tuple (struct)/slice.
+ /// Return a sequence of corresponding patterns, and the index and the span of `..` if it
+ /// exists.
+ /// Each sub-assignment is recorded in `assignments`.
+ fn destructure_sequence(
+ &mut self,
+ elements: &[AstP<Expr>],
+ ctx: &str,
+ eq_sign_span: Span,
+ assignments: &mut Vec<hir::Stmt<'hir>>,
+ ) -> (&'hir [hir::Pat<'hir>], Option<(usize, Span)>) {
+ let mut rest = None;
+ let elements =
+ self.arena.alloc_from_iter(elements.iter().enumerate().filter_map(|(i, e)| {
+ // Check for `..` pattern.
+ if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+ if let Some((_, prev_span)) = rest {
+ self.ban_extra_rest_pat(e.span, prev_span, ctx);
+ } else {
+ rest = Some((i, e.span));
+ }
+ None
+ } else {
+ Some(self.destructure_assign_mut(e, eq_sign_span, assignments))
+ }
+ }));
+ (elements, rest)
+ }
+
+ /// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
+ fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
+ let e1 = self.lower_expr_mut(e1);
+ let e2 = self.lower_expr_mut(e2);
+ let fn_path =
+ hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span), None);
+ let fn_expr =
+ self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
+ hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
+ }
+
+ fn lower_expr_range(
+ &mut self,
+ span: Span,
+ e1: Option<&Expr>,
+ e2: Option<&Expr>,
+ lims: RangeLimits,
+ ) -> hir::ExprKind<'hir> {
+ use rustc_ast::RangeLimits::*;
+
+ let lang_item = match (e1, e2, lims) {
+ (None, None, HalfOpen) => hir::LangItem::RangeFull,
+ (Some(..), None, HalfOpen) => hir::LangItem::RangeFrom,
+ (None, Some(..), HalfOpen) => hir::LangItem::RangeTo,
+ (Some(..), Some(..), HalfOpen) => hir::LangItem::Range,
+ (None, Some(..), Closed) => hir::LangItem::RangeToInclusive,
+ (Some(..), Some(..), Closed) => unreachable!(),
+ (_, None, Closed) => self.diagnostic().span_fatal(span, "inclusive range with no end"),
+ };
+
+ let fields = self.arena.alloc_from_iter(
+ e1.iter().map(|e| (sym::start, e)).chain(e2.iter().map(|e| (sym::end, e))).map(
+ |(s, e)| {
+ let expr = self.lower_expr(&e);
+ let ident = Ident::new(s, self.lower_span(e.span));
+ self.expr_field(ident, expr, e.span)
+ },
+ ),
+ );
+
+ hir::ExprKind::Struct(
+ self.arena.alloc(hir::QPath::LangItem(lang_item, self.lower_span(span), None)),
+ fields,
+ None,
+ )
+ }
+
+ fn lower_label(&self, opt_label: Option<Label>) -> Option<Label> {
+ let label = opt_label?;
+ Some(Label { ident: self.lower_ident(label.ident) })
+ }
+
+ fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
+ let target_id = match destination {
+ Some((id, _)) => {
+ if let Some(loop_id) = self.resolver.get_label_res(id) {
+ Ok(self.lower_node_id(loop_id))
+ } else {
+ Err(hir::LoopIdError::UnresolvedLabel)
+ }
+ }
+ None => self
+ .loop_scope
+ .map(|id| Ok(self.lower_node_id(id)))
+ .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope)),
+ };
+ let label = self.lower_label(destination.map(|(_, label)| label));
+ hir::Destination { label, target_id }
+ }
+
+ fn lower_jump_destination(&mut self, id: NodeId, opt_label: Option<Label>) -> hir::Destination {
+ if self.is_in_loop_condition && opt_label.is_none() {
+ hir::Destination {
+ label: None,
+ target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition),
+ }
+ } else {
+ self.lower_loop_destination(opt_label.map(|label| (id, label)))
+ }
+ }
+
+ fn with_catch_scope<T>(&mut self, catch_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
+ let old_scope = self.catch_scope.replace(catch_id);
+ let result = f(self);
+ self.catch_scope = old_scope;
+ result
+ }
+
+ fn with_loop_scope<T>(&mut self, loop_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
+ // We're no longer in the base loop's condition; we're in another loop.
+ let was_in_loop_condition = self.is_in_loop_condition;
+ self.is_in_loop_condition = false;
+
+ let old_scope = self.loop_scope.replace(loop_id);
+ let result = f(self);
+ self.loop_scope = old_scope;
+
+ self.is_in_loop_condition = was_in_loop_condition;
+
+ result
+ }
+
+ fn with_loop_condition_scope<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
+ let was_in_loop_condition = self.is_in_loop_condition;
+ self.is_in_loop_condition = true;
+
+ let result = f(self);
+
+ self.is_in_loop_condition = was_in_loop_condition;
+
+ result
+ }
+
+ fn lower_expr_field(&mut self, f: &ExprField) -> hir::ExprField<'hir> {
+ hir::ExprField {
+ hir_id: self.next_id(),
+ ident: self.lower_ident(f.ident),
+ expr: self.lower_expr(&f.expr),
+ span: self.lower_span(f.span),
+ is_shorthand: f.is_shorthand,
+ }
+ }
+
+ fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
+ match self.generator_kind {
+ Some(hir::GeneratorKind::Gen) => {}
+ Some(hir::GeneratorKind::Async(_)) => {
+ struct_span_err!(
+ self.tcx.sess,
+ span,
+ E0727,
+ "`async` generators are not yet supported"
+ )
+ .emit();
+ }
+ None => self.generator_kind = Some(hir::GeneratorKind::Gen),
+ }
+
+ let expr =
+ opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
+
+ hir::ExprKind::Yield(expr, hir::YieldSource::Yield)
+ }
+
+ /// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into:
+ /// ```ignore (pseudo-rust)
+ /// {
+ /// let result = match IntoIterator::into_iter(<head>) {
+ /// mut iter => {
+ /// [opt_ident]: loop {
+ /// match Iterator::next(&mut iter) {
+ /// None => break,
+ /// Some(<pat>) => <body>,
+ /// };
+ /// }
+ /// }
+ /// };
+ /// result
+ /// }
+ /// ```
+ fn lower_expr_for(
+ &mut self,
+ e: &Expr,
+ pat: &Pat,
+ head: &Expr,
+ body: &Block,
+ opt_label: Option<Label>,
+ ) -> hir::Expr<'hir> {
+ let head = self.lower_expr_mut(head);
+ let pat = self.lower_pat(pat);
+ let for_span =
+ self.mark_span_with_reason(DesugaringKind::ForLoop, self.lower_span(e.span), None);
+ let head_span = self.mark_span_with_reason(DesugaringKind::ForLoop, head.span, None);
+ let pat_span = self.mark_span_with_reason(DesugaringKind::ForLoop, pat.span, None);
+
+ // `None => break`
+ let none_arm = {
+ let break_expr =
+ self.with_loop_scope(e.id, |this| this.expr_break_alloc(for_span, ThinVec::new()));
+ let pat = self.pat_none(for_span);
+ self.arm(pat, break_expr)
+ };
+
+ // Some(<pat>) => <body>,
+ let some_arm = {
+ let some_pat = self.pat_some(pat_span, pat);
+ let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
+ let body_expr = self.arena.alloc(self.expr_block(body_block, ThinVec::new()));
+ self.arm(some_pat, body_expr)
+ };
+
+ // `mut iter`
+ let iter = Ident::with_dummy_span(sym::iter);
+ let (iter_pat, iter_pat_nid) =
+ self.pat_ident_binding_mode(head_span, iter, hir::BindingAnnotation::Mutable);
+
+ // `match Iterator::next(&mut iter) { ... }`
+ let match_expr = {
+ let iter = self.expr_ident(head_span, iter, iter_pat_nid);
+ let ref_mut_iter = self.expr_mut_addr_of(head_span, iter);
+ let next_expr = self.expr_call_lang_item_fn(
+ head_span,
+ hir::LangItem::IteratorNext,
+ arena_vec![self; ref_mut_iter],
+ None,
+ );
+ let arms = arena_vec![self; none_arm, some_arm];
+
+ self.expr_match(head_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
+ };
+ let match_stmt = self.stmt_expr(for_span, match_expr);
+
+ let loop_block = self.block_all(for_span, arena_vec![self; match_stmt], None);
+
+ // `[opt_ident]: loop { ... }`
+ let kind = hir::ExprKind::Loop(
+ loop_block,
+ self.lower_label(opt_label),
+ hir::LoopSource::ForLoop,
+ self.lower_span(for_span.with_hi(head.span.hi())),
+ );
+ let loop_expr =
+ self.arena.alloc(hir::Expr { hir_id: self.lower_node_id(e.id), kind, span: for_span });
+
+ // `mut iter => { ... }`
+ let iter_arm = self.arm(iter_pat, loop_expr);
+
+ // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
+ let into_iter_expr = {
+ self.expr_call_lang_item_fn(
+ head_span,
+ hir::LangItem::IntoIterIntoIter,
+ arena_vec![self; head],
+ None,
+ )
+ };
+
+ let match_expr = self.arena.alloc(self.expr_match(
+ for_span,
+ into_iter_expr,
+ arena_vec![self; iter_arm],
+ hir::MatchSource::ForLoopDesugar,
+ ));
+
+ let attrs: Vec<_> = e.attrs.iter().map(|a| self.lower_attr(a)).collect();
+
+ // This is effectively `{ let _result = ...; _result }`.
+ // The construct was introduced in #21984 and is necessary to make sure that
+ // temporaries in the `head` expression are dropped and do not leak to the
+ // surrounding scope of the `match` since the `match` is not a terminating scope.
+ //
+ // Also, add the attributes to the outer returned expr node.
+ self.expr_drop_temps_mut(for_span, match_expr, attrs.into())
+ }
+
+ /// Desugar `ExprKind::Try` from: `<expr>?` into:
+ /// ```ignore (pseudo-rust)
+ /// match Try::branch(<expr>) {
+ /// ControlFlow::Continue(val) => #[allow(unreachable_code)] val,,
+ /// ControlFlow::Break(residual) =>
+ /// #[allow(unreachable_code)]
+ /// // If there is an enclosing `try {...}`:
+ /// break 'catch_target Try::from_residual(residual),
+ /// // Otherwise:
+ /// return Try::from_residual(residual),
+ /// }
+ /// ```
+ fn lower_expr_try(&mut self, span: Span, sub_expr: &Expr) -> hir::ExprKind<'hir> {
+ let unstable_span = self.mark_span_with_reason(
+ DesugaringKind::QuestionMark,
+ span,
+ self.allow_try_trait.clone(),
+ );
+ let try_span = self.tcx.sess.source_map().end_point(span);
+ let try_span = self.mark_span_with_reason(
+ DesugaringKind::QuestionMark,
+ try_span,
+ self.allow_try_trait.clone(),
+ );
+
+ // `Try::branch(<expr>)`
+ let scrutinee = {
+ // expand <expr>
+ let sub_expr = self.lower_expr_mut(sub_expr);
+
+ self.expr_call_lang_item_fn(
+ unstable_span,
+ hir::LangItem::TryTraitBranch,
+ arena_vec![self; sub_expr],
+ None,
+ )
+ };
+
+ // `#[allow(unreachable_code)]`
+ let attr = {
+ // `allow(unreachable_code)`
+ let allow = {
+ let allow_ident = Ident::new(sym::allow, self.lower_span(span));
+ let uc_ident = Ident::new(sym::unreachable_code, self.lower_span(span));
+ let uc_nested = attr::mk_nested_word_item(uc_ident);
+ attr::mk_list_item(allow_ident, vec![uc_nested])
+ };
+ attr::mk_attr_outer(allow)
+ };
+ let attrs = vec![attr];
+
+ // `ControlFlow::Continue(val) => #[allow(unreachable_code)] val,`
+ let continue_arm = {
+ let val_ident = Ident::with_dummy_span(sym::val);
+ let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
+ let val_expr = self.arena.alloc(self.expr_ident_with_attrs(
+ span,
+ val_ident,
+ val_pat_nid,
+ ThinVec::from(attrs.clone()),
+ ));
+ let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
+ self.arm(continue_pat, val_expr)
+ };
+
+ // `ControlFlow::Break(residual) =>
+ // #[allow(unreachable_code)]
+ // return Try::from_residual(residual),`
+ let break_arm = {
+ let residual_ident = Ident::with_dummy_span(sym::residual);
+ let (residual_local, residual_local_nid) = self.pat_ident(try_span, residual_ident);
+ let residual_expr = self.expr_ident_mut(try_span, residual_ident, residual_local_nid);
+ let from_residual_expr = self.wrap_in_try_constructor(
+ hir::LangItem::TryTraitFromResidual,
+ try_span,
+ self.arena.alloc(residual_expr),
+ unstable_span,
+ );
+ let thin_attrs = ThinVec::from(attrs);
+ let ret_expr = if let Some(catch_node) = self.catch_scope {
+ let target_id = Ok(self.lower_node_id(catch_node));
+ self.arena.alloc(self.expr(
+ try_span,
+ hir::ExprKind::Break(
+ hir::Destination { label: None, target_id },
+ Some(from_residual_expr),
+ ),
+ thin_attrs,
+ ))
+ } else {
+ self.arena.alloc(self.expr(
+ try_span,
+ hir::ExprKind::Ret(Some(from_residual_expr)),
+ thin_attrs,
+ ))
+ };
+
+ let break_pat = self.pat_cf_break(try_span, residual_local);
+ self.arm(break_pat, ret_expr)
+ };
+
+ hir::ExprKind::Match(
+ scrutinee,
+ arena_vec![self; break_arm, continue_arm],
+ hir::MatchSource::TryDesugar,
+ )
+ }
+
+ /// Desugar `ExprKind::Yeet` from: `do yeet <expr>` into:
+ /// ```rust
+ /// // If there is an enclosing `try {...}`:
+ /// break 'catch_target FromResidual::from_residual(Yeet(residual)),
+ /// // Otherwise:
+ /// return FromResidual::from_residual(Yeet(residual)),
+ /// ```
+ /// But to simplify this, there's a `from_yeet` lang item function which
+ /// handles the combined `FromResidual::from_residual(Yeet(residual))`.
+ fn lower_expr_yeet(&mut self, span: Span, sub_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
+ // The expression (if present) or `()` otherwise.
+ let (yeeted_span, yeeted_expr) = if let Some(sub_expr) = sub_expr {
+ (sub_expr.span, self.lower_expr(sub_expr))
+ } else {
+ (self.mark_span_with_reason(DesugaringKind::YeetExpr, span, None), self.expr_unit(span))
+ };
+
+ let unstable_span = self.mark_span_with_reason(
+ DesugaringKind::YeetExpr,
+ span,
+ self.allow_try_trait.clone(),
+ );
+
+ let from_yeet_expr = self.wrap_in_try_constructor(
+ hir::LangItem::TryTraitFromYeet,
+ unstable_span,
+ yeeted_expr,
+ yeeted_span,
+ );
+
+ if let Some(catch_node) = self.catch_scope {
+ let target_id = Ok(self.lower_node_id(catch_node));
+ hir::ExprKind::Break(hir::Destination { label: None, target_id }, Some(from_yeet_expr))
+ } else {
+ hir::ExprKind::Ret(Some(from_yeet_expr))
+ }
+ }
+
+ // =========================================================================
+ // Helper methods for building HIR.
+ // =========================================================================
+
+ /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
+ ///
+ /// In terms of drop order, it has the same effect as wrapping `expr` in
+ /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
+ ///
+ /// The drop order can be important in e.g. `if expr { .. }`.
+ pub(super) fn expr_drop_temps(
+ &mut self,
+ span: Span,
+ expr: &'hir hir::Expr<'hir>,
+ attrs: AttrVec,
+ ) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.expr_drop_temps_mut(span, expr, attrs))
+ }
+
+ pub(super) fn expr_drop_temps_mut(
+ &mut self,
+ span: Span,
+ expr: &'hir hir::Expr<'hir>,
+ attrs: AttrVec,
+ ) -> hir::Expr<'hir> {
+ self.expr(span, hir::ExprKind::DropTemps(expr), attrs)
+ }
+
+ fn expr_match(
+ &mut self,
+ span: Span,
+ arg: &'hir hir::Expr<'hir>,
+ arms: &'hir [hir::Arm<'hir>],
+ source: hir::MatchSource,
+ ) -> hir::Expr<'hir> {
+ self.expr(span, hir::ExprKind::Match(arg, arms, source), ThinVec::new())
+ }
+
+ fn expr_break(&mut self, span: Span, attrs: AttrVec) -> hir::Expr<'hir> {
+ let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
+ self.expr(span, expr_break, attrs)
+ }
+
+ fn expr_break_alloc(&mut self, span: Span, attrs: AttrVec) -> &'hir hir::Expr<'hir> {
+ let expr_break = self.expr_break(span, attrs);
+ self.arena.alloc(expr_break)
+ }
+
+ fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
+ self.expr(
+ span,
+ hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e),
+ ThinVec::new(),
+ )
+ }
+
+ fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[]), ThinVec::new()))
+ }
+
+ fn expr_call_mut(
+ &mut self,
+ span: Span,
+ e: &'hir hir::Expr<'hir>,
+ args: &'hir [hir::Expr<'hir>],
+ ) -> hir::Expr<'hir> {
+ self.expr(span, hir::ExprKind::Call(e, args), ThinVec::new())
+ }
+
+ fn expr_call(
+ &mut self,
+ span: Span,
+ e: &'hir hir::Expr<'hir>,
+ args: &'hir [hir::Expr<'hir>],
+ ) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.expr_call_mut(span, e, args))
+ }
+
+ fn expr_call_lang_item_fn_mut(
+ &mut self,
+ span: Span,
+ lang_item: hir::LangItem,
+ args: &'hir [hir::Expr<'hir>],
+ hir_id: Option<hir::HirId>,
+ ) -> hir::Expr<'hir> {
+ let path =
+ self.arena.alloc(self.expr_lang_item_path(span, lang_item, ThinVec::new(), hir_id));
+ self.expr_call_mut(span, path, args)
+ }
+
+ fn expr_call_lang_item_fn(
+ &mut self,
+ span: Span,
+ lang_item: hir::LangItem,
+ args: &'hir [hir::Expr<'hir>],
+ hir_id: Option<hir::HirId>,
+ ) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args, hir_id))
+ }
+
+ fn expr_lang_item_path(
+ &mut self,
+ span: Span,
+ lang_item: hir::LangItem,
+ attrs: AttrVec,
+ hir_id: Option<hir::HirId>,
+ ) -> hir::Expr<'hir> {
+ self.expr(
+ span,
+ hir::ExprKind::Path(hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id)),
+ attrs,
+ )
+ }
+
+ pub(super) fn expr_ident(
+ &mut self,
+ sp: Span,
+ ident: Ident,
+ binding: hir::HirId,
+ ) -> &'hir hir::Expr<'hir> {
+ self.arena.alloc(self.expr_ident_mut(sp, ident, binding))
+ }
+
+ pub(super) fn expr_ident_mut(
+ &mut self,
+ sp: Span,
+ ident: Ident,
+ binding: hir::HirId,
+ ) -> hir::Expr<'hir> {
+ self.expr_ident_with_attrs(sp, ident, binding, ThinVec::new())
+ }
+
+ fn expr_ident_with_attrs(
+ &mut self,
+ span: Span,
+ ident: Ident,
+ binding: hir::HirId,
+ attrs: AttrVec,
+ ) -> hir::Expr<'hir> {
+ let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
+ None,
+ self.arena.alloc(hir::Path {
+ span: self.lower_span(span),
+ res: Res::Local(binding),
+ segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
+ }),
+ ));
+
+ self.expr(span, expr_path, attrs)
+ }
+
+ fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
+ let hir_id = self.next_id();
+ let span = expr.span;
+ self.expr(
+ span,
+ hir::ExprKind::Block(
+ self.arena.alloc(hir::Block {
+ stmts: &[],
+ expr: Some(expr),
+ hir_id,
+ rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
+ span: self.lower_span(span),
+ targeted_by_break: false,
+ }),
+ None,
+ ),
+ ThinVec::new(),
+ )
+ }
+
+ fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
+ let blk = self.block_all(span, &[], None);
+ let expr = self.expr_block(blk, ThinVec::new());
+ self.arena.alloc(expr)
+ }
+
+ pub(super) fn expr_block(
+ &mut self,
+ b: &'hir hir::Block<'hir>,
+ attrs: AttrVec,
+ ) -> hir::Expr<'hir> {
+ self.expr(b.span, hir::ExprKind::Block(b, None), attrs)
+ }
+
+ pub(super) fn expr(
+ &mut self,
+ span: Span,
+ kind: hir::ExprKind<'hir>,
+ attrs: AttrVec,
+ ) -> hir::Expr<'hir> {
+ let hir_id = self.next_id();
+ self.lower_attrs(hir_id, &attrs);
+ hir::Expr { hir_id, kind, span: self.lower_span(span) }
+ }
+
+ fn expr_field(
+ &mut self,
+ ident: Ident,
+ expr: &'hir hir::Expr<'hir>,
+ span: Span,
+ ) -> hir::ExprField<'hir> {
+ hir::ExprField {
+ hir_id: self.next_id(),
+ ident,
+ span: self.lower_span(span),
+ expr,
+ is_shorthand: false,
+ }
+ }
+
+ fn arm(&mut self, pat: &'hir hir::Pat<'hir>, expr: &'hir hir::Expr<'hir>) -> hir::Arm<'hir> {
+ hir::Arm {
+ hir_id: self.next_id(),
+ pat,
+ guard: None,
+ span: self.lower_span(expr.span),
+ body: expr,
+ }
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-02 21:14:46 +0000