Lowering: Fuse ExprKind::While logic + Cleanup.
This commit is contained in:
Mazdak Farrokhzad
parent
547735457f
commit
26144fe869
@ -4394,20 +4394,17 @@ impl<'a> LoweringContext<'a> {
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let then_blk = self.lower_block(then, false);
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let then_expr = self.expr_block(then_blk, ThinVec::new());
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let (then_pats, scrutinee, desugar) = match cond.node {
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// `<pat> => <then>`
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// `<pat> => <then>`:
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ExprKind::Let(ref pats, ref scrutinee) => {
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let scrutinee = self.lower_expr(scrutinee);
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let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
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let desugar = hir::MatchSource::IfLetDesugar { contains_else_clause };
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(pats, scrutinee, desugar)
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}
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// `true => then`:
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// `true => <then>`:
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_ => {
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// Lower condition:
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let cond = self.lower_expr(cond);
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// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
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// to preserve drop semantics since `if cond { ... }`
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// don't let temporaries live outside of `cond`.
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let span_block = self.mark_span_with_reason(CondTemporary, cond.span, None);
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// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
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// to preserve drop semantics since `if cond { ... }` does not
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@ -4424,61 +4421,36 @@ impl<'a> LoweringContext<'a> {
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hir::ExprKind::Match(P(scrutinee), vec![then_arm, else_arm].into(), desugar)
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}
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// FIXME(#53667): handle lowering of && and parens.
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ExprKind::While(ref cond, ref body, opt_label) => {
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// Desugar `ExprWhileLet`
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// from: `[opt_ident]: while let <pat> = <sub_expr> <body>`
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if let ExprKind::Let(ref pats, ref sub_expr) = cond.node {
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// to:
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//
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// [opt_ident]: loop {
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// match <sub_expr> {
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// <pat> => <body>,
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// _ => break
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// }
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// }
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ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
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// Note that the block AND the condition are evaluated in the loop scope.
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// This is done to allow `break` from inside the condition of the loop.
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// Note that the block AND the condition are evaluated in the loop scope.
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// This is done to allow `break` from inside the condition of the loop.
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let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| {
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(
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this.lower_block(body, false),
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this.expr_break(e.span, ThinVec::new()),
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this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
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)
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});
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// `_ => break`:
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let else_arm = {
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let else_pat = this.pat_wild(e.span);
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let else_expr = this.expr_break(e.span, ThinVec::new());
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this.arm(hir_vec![else_pat], else_expr)
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};
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// `<pat> => <body>`
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let pat_arm = {
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let body_expr = P(self.expr_block(body, ThinVec::new()));
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let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
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self.arm(pats, body_expr)
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};
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// `_ => break`
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let break_arm = {
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let pat_under = self.pat_wild(e.span);
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self.arm(hir_vec![pat_under], break_expr)
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};
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// `match <sub_expr> { ... }`
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let match_expr = self.expr_match(
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sub_expr.span,
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sub_expr,
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hir_vec![pat_arm, break_arm],
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hir::MatchSource::WhileLetDesugar,
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);
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// `[opt_ident]: loop { ... }`
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let loop_block = P(self.block_expr(P(match_expr)));
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let loop_expr = hir::ExprKind::Loop(
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loop_block,
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self.lower_label(opt_label),
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hir::LoopSource::WhileLet,
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);
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// Add attributes to the outer returned expr node.
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loop_expr
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} else {
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self.with_loop_scope(e.id, |this| {
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// Handle then + scrutinee:
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let then_blk = this.lower_block(body, false);
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let then_expr = this.expr_block(then_blk, ThinVec::new());
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let (then_pats, scrutinee, desugar, source) = match cond.node {
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ExprKind::Let(ref pats, ref scrutinee) => {
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// to:
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//
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// [opt_ident]: loop {
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// match <sub_expr> {
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// <pat> => <body>,
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// _ => break
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// }
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// }
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let scrutinee = this.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
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let pats = pats.iter().map(|pat| this.lower_pat(pat)).collect();
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let desugar = hir::MatchSource::WhileLetDesugar;
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(pats, scrutinee, desugar, hir::LoopSource::WhileLet)
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}
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_ => {
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// We desugar: `'label: while $cond $body` into:
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//
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// ```
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@ -4490,40 +4462,37 @@ impl<'a> LoweringContext<'a> {
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// }
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// ```
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// `true => then`:
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let then_pat = this.pat_bool(e.span, true);
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let then_blk = this.lower_block(body, false);
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let then_expr = this.expr_block(then_blk, ThinVec::new());
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let then_arm = this.arm(hir_vec![then_pat], P(then_expr));
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// `_ => break`:
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let else_pat = this.pat_wild(e.span);
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let else_expr = this.expr_break(e.span, ThinVec::new());
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let else_arm = this.arm(hir_vec![else_pat], else_expr);
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// Lower condition:
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let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
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let cond = this.with_loop_condition_scope(|this| this.lower_expr(cond));
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let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
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// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
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// to preserve drop semantics since `if cond { ... }` does not
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// to preserve drop semantics since `while cond { ... }` does not
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// let temporaries live outside of `cond`.
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let cond = this.expr_drop_temps(span_block, P(cond), ThinVec::new());
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let match_expr = this.expr_match(
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cond.span,
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P(cond),
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vec![then_arm, else_arm].into(),
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hir::MatchSource::WhileDesugar,
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);
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let desugar = hir::MatchSource::WhileDesugar;
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// `true => <then>`:
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let pats = hir_vec![this.pat_bool(e.span, true)];
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(pats, cond, desugar, hir::LoopSource::While)
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}
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};
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let then_arm = this.arm(then_pats, P(then_expr));
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hir::ExprKind::Loop(
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P(this.block_expr(P(match_expr))),
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this.lower_label(opt_label),
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hir::LoopSource::While,
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)
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})
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}
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}
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// `match <scrutinee> { ... }`
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let match_expr = this.expr_match(
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scrutinee.span,
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P(scrutinee),
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hir_vec![then_arm, else_arm],
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desugar,
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);
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// `[opt_ident]: loop { ... }`
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hir::ExprKind::Loop(
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P(this.block_expr(P(match_expr))),
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this.lower_label(opt_label),
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source
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)
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}),
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ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
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hir::ExprKind::Loop(
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this.lower_block(body, false),
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