This draws a clear distinction between the fields/methods that are needed by
initial span extraction and preprocessing, and those that are needed by the
main "refinement" loop.
These two tasks historically needed to be interleaved, but after various recent
changes (including #116046 and #116917) they can now be fully separated.
This method is trying to detect macro invocations, so that it can split a span
into two parts just after the `!` of the invocation.
Under some circumstances (probably involving nested macros), it gets confused
and produces a span that is larger than the original span, and possibly extends
outside its enclosing function and even into an adjacent file.
In extreme cases, that can result in malformed coverage mappings that cause
`llvm-cov` to fail. For now, we at least want to detect these egregious cases
and avoid them, so that coverage reports can still be produced.
coverage: Fix inconsistent handling of function signature spans
While doing some more cleanup of `spans`, I noticed a strange inconsistency in how function signatures are handled. Normally the function signature span is treated as though it were executable as part of the start of the function, but in some cases the signature span disappears entirely from coverage, for no obvious reason.
This is caused by the fact that spans created by `CoverageSpan::for_fn_sig` don't add the span to their `merged_spans` field (unlike normal statement/terminator spans). In cases where the span-processing code looks at those merged spans, it thinks the signature span is no longer visible and deletes it.
Adding the signature span to `merged_spans` resolves the inconsistency.
(Prior to #116409 this wouldn't have been possible, because there was no case in the old `CoverageStatement` enum representing a signature. Now that `merged_spans` is just a list of spans, that's no longer an obstacle.)
Interacting with `basic_coverage_blocks` directly makes it easier to satisfy
the borrow checker when mutating `pending_dups` while reading other fields.
This enum was mainly needed to track the precise origin of a span in MIR, for
debug printing purposes. Since the old debug code was removed in #115962, we
can replace it with just the span itself.
If a BCB has more than one code region, those extra regions can now all be
stored in the same coverage statement, instead of being stored in additional
statements.
By encapsulating the coverage spans in a struct, we can change the internal
representation without disturbing existing call sites. This will be useful for
grouping coverage spans by BCB.
This patch includes some changes that were originally in #115912, which avoid
the need for a particular test to deal with coverage spans at all.
(Comments/logs referring to `CoverageSpan` are updated in a subsequent patch.)
This code was calling `sort_unstable_by`, but failed to impose a total order on
the initial spans. That resulted in unpredictable handling of closure spans,
producing inconsistencies in the coverage maps and in user-visible coverage
reports.
This patch fixes the problem by always sorting closure spans before
otherwise-identical non-closure spans, and also switches to a stable sort in
case the ordering is still not total.
