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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_ast_lowering/src/expr.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_ast_lowering/src/expr.rs')
-rw-r--r-- | compiler/rustc_ast_lowering/src/expr.rs | 1914 |
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, + } + } +} |