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lowering: extract lower_expr_while_in_loop_scope

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This commit is contained in:
Mazdak Farrokhzad 2019-08-10 15:28:57 +02:00
parent c8b3b2e052
commit 11251b9dab
1 changed files with 86 additions and 73 deletions
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159
src/librustc/hir/lowering/expr.rs
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@ -143,80 +143,8 @@ impl LoweringContext<'_> {
hir::ExprKind::Match(P(scrutinee), vec![then_arm, else_arm].into(), desugar)
}
// FIXME(#53667): handle lowering of && and parens.
ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
// Note that the block AND the condition are evaluated in the loop scope.
// This is done to allow `break` from inside the condition of the loop.
// `_ => break`:
let else_arm = {
let else_pat = this.pat_wild(e.span);
let else_expr = this.expr_break(e.span, ThinVec::new());
this.arm(hir_vec![else_pat], else_expr)
};
// Handle then + scrutinee:
let then_blk = this.lower_block(body, false);
let then_expr = this.expr_block(then_blk, ThinVec::new());
let (then_pats, scrutinee, desugar, source) = match cond.node {
ExprKind::Let(ref pats, ref scrutinee) => {
// to:
//
// [opt_ident]: loop {
// match <sub_expr> {
// <pat> => <body>,
// _ => break
// }
// }
let scrutinee = this.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
let pats = pats.iter().map(|pat| this.lower_pat(pat)).collect();
let desugar = hir::MatchSource::WhileLetDesugar;
(pats, scrutinee, desugar, hir::LoopSource::WhileLet)
}
_ => {
// We desugar: `'label: while $cond $body` into:
//
// ```
// 'label: loop {
// match DropTemps($cond) {
// true => $body,
// _ => break,
// }
// }
// ```
// Lower condition:
let cond = this.with_loop_condition_scope(|this| this.lower_expr(cond));
let span_block = this.mark_span_with_reason(
DesugaringKind::CondTemporary, cond.span, None
);
// 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`.
let cond = this.expr_drop_temps(span_block, P(cond), ThinVec::new());
let desugar = hir::MatchSource::WhileDesugar;
// `true => <then>`:
let pats = hir_vec![this.pat_bool(e.span, true)];
(pats, cond, desugar, hir::LoopSource::While)
}
};
let then_arm = this.arm(then_pats, P(then_expr));
// `match <scrutinee> { ... }`
let match_expr = this.expr_match(
scrutinee.span,
P(scrutinee),
hir_vec![then_arm, else_arm],
desugar,
);
// `[opt_ident]: loop { ... }`
hir::ExprKind::Loop(
P(this.block_expr(P(match_expr))),
this.lower_label(opt_label),
source
)
this.lower_expr_while_in_loop_scope(e.span, cond, body, opt_label)
}),
ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
hir::ExprKind::Loop(
@ -351,6 +279,91 @@ impl LoweringContext<'_> {
}
}
fn lower_expr_while_in_loop_scope(
&mut self,
span: Span,
cond: &Expr,
body: &Block,
opt_label: Option<Label>
) -> hir::ExprKind {
// FIXME(#53667): handle lowering of && and parens.
// Note that the block AND the condition are evaluated in the loop scope.
// This is done to allow `break` from inside the condition of the loop.
// `_ => break`:
let else_arm = {
let else_pat = self.pat_wild(span);
let else_expr = self.expr_break(span, ThinVec::new());
self.arm(hir_vec![else_pat], else_expr)
};
// Handle then + scrutinee:
let then_blk = self.lower_block(body, false);
let then_expr = self.expr_block(then_blk, ThinVec::new());
let (then_pats, scrutinee, desugar, source) = match cond.node {
ExprKind::Let(ref pats, ref scrutinee) => {
// to:
//
// [opt_ident]: loop {
// match <sub_expr> {
// <pat> => <body>,
// _ => break
// }
// }
let scrutinee = self.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
let desugar = hir::MatchSource::WhileLetDesugar;
(pats, scrutinee, desugar, hir::LoopSource::WhileLet)
}
_ => {
// We desugar: `'label: while $cond $body` into:
//
// ```
// 'label: loop {
// match DropTemps($cond) {
// true => $body,
// _ => break,
// }
// }
// ```
// Lower condition:
let cond = self.with_loop_condition_scope(|this| this.lower_expr(cond));
let span_block = self.mark_span_with_reason(
DesugaringKind::CondTemporary,
cond.span,
None,
);
// 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`.
let cond = self.expr_drop_temps(span_block, P(cond), ThinVec::new());
let desugar = hir::MatchSource::WhileDesugar;
// `true => <then>`:
let pats = hir_vec![self.pat_bool(span, true)];
(pats, cond, desugar, hir::LoopSource::While)
}
};
let then_arm = self.arm(then_pats, P(then_expr));
// `match <scrutinee> { ... }`
let match_expr = self.expr_match(
scrutinee.span,
P(scrutinee),
hir_vec![then_arm, else_arm],
desugar,
);
// `[opt_ident]: loop { ... }`
hir::ExprKind::Loop(
P(self.block_expr(P(match_expr))),
self.lower_label(opt_label),
source
)
}
fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind {
self.with_catch_scope(body.id, |this| {
let unstable_span = this.mark_span_with_reason(