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coverage: Explain why we temporarily steal pending_dups

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Zalathar 2023-10-14 23:59:11 +11:00
parent 5e5a8e7769
commit 7aa1b8390b
1 changed files with 20 additions and 6 deletions
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26
compiler/rustc_mir_transform/src/coverage/spans.rs
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@ -353,8 +353,10 @@ impl<'a> CoverageSpansGenerator<'a> {
let prev = self.take_prev();
debug!(" AT END, adding last prev={prev:?}");
let pending_dups = self.pending_dups.split_off(0);
for dup in pending_dups {
// Take `pending_dups` so that we can drain it while calling self methods.
// It is never used as a field after this point.
for dup in std::mem::take(&mut self.pending_dups) {
debug!(" ...adding at least one pending dup={:?}", dup);
self.push_refined_span(dup);
}
@ -474,11 +476,16 @@ impl<'a> CoverageSpansGenerator<'a> {
previous iteration, or prev started a new disjoint span"
);
if last_dup.span.hi() <= self.curr().span.lo() {
let pending_dups = self.pending_dups.split_off(0);
for dup in pending_dups.into_iter() {
// Temporarily steal `pending_dups` into a local, so that we can
// drain it while calling other self methods.
let mut pending_dups = std::mem::take(&mut self.pending_dups);
for dup in pending_dups.drain(..) {
debug!(" ...adding at least one pending={:?}", dup);
self.push_refined_span(dup);
}
// The list of dups is now empty, but we can recycle its capacity.
assert!(pending_dups.is_empty() && self.pending_dups.is_empty());
self.pending_dups = pending_dups;
} else {
self.pending_dups.clear();
}
@ -526,7 +533,10 @@ impl<'a> CoverageSpansGenerator<'a> {
let has_pre_closure_span = prev.span.lo() < right_cutoff;
let has_post_closure_span = prev.span.hi() > right_cutoff;
let mut pending_dups = self.pending_dups.split_off(0);
// Temporarily steal `pending_dups` into a local, so that we can
// mutate and/or drain it while calling other self methods.
let mut pending_dups = std::mem::take(&mut self.pending_dups);
if has_pre_closure_span {
let mut pre_closure = self.prev().clone();
pre_closure.span = pre_closure.span.with_hi(left_cutoff);
@ -540,6 +550,7 @@ impl<'a> CoverageSpansGenerator<'a> {
}
self.push_refined_span(pre_closure);
}
if has_post_closure_span {
// Mutate `prev.span()` to start after the closure (and discard curr).
// (**NEVER** update `prev_original_span` because it affects the assumptions
@ -550,12 +561,15 @@ impl<'a> CoverageSpansGenerator<'a> {
debug!(" ...and at least one overlapping dup={:?}", dup);
dup.span = dup.span.with_lo(right_cutoff);
}
self.pending_dups.append(&mut pending_dups);
let closure_covspan = self.take_curr(); // Prevent this curr from becoming prev.
self.push_refined_span(closure_covspan); // since self.prev() was already updated
} else {
pending_dups.clear();
}
// Restore the modified post-closure spans, or the empty vector's capacity.
assert!(self.pending_dups.is_empty());
self.pending_dups = pending_dups;
}
/// Called if `curr.span` equals `prev_original_span` (and potentially equal to all