Fix 2.13.15-only false positives with -Wunused:patvars
#10870
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lrytz
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Oct 9, 2024
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@som-snytt I added a release-note, hopefully an accurate one |
SethTisue
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-Wunused:patvars
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Fixes false positives from
-Wunused:patvarsin the presence of filters (if) — this was scala/bug#13041.Note that
-Wunused:patvarsis part of-Wunusedbut is not enabled by-Xlint. With this fix, interested users may wish to make a fresh attempt to add-Wunused:patvarsto their builds.The now-correct position information may also aid tooling, as seen in scala/bug#13037 .
Followup to #10812, which (in 2.13.15) expanded unused checking into this area.
Fixes scala/bug#13041
Fixes scala/bug#13037
Implementation notes
Summary: Track patvars by position (and correct span of guard closure)
The scheme of linking duplicated patvar trees via attachments is brittle because links are stale after duplication; in particular, they point to old trees which may not be typechecked, so symbols are not recoverable.
Instead, just identify associated trees by position: duplicates have a focused position and the "original" has its opaque range.
Fix range of guard closure in TreeGen.mkFor to include parameter. (In the previous scheme, the pattern and its duplicate were swapped to build the "links", but now have been swapped back again, so that bug is nullified.)
Some mild refactoring of position validation for readability.