fix: preserve TermInfo for do-match discriminant variables#12666
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fix: preserve TermInfo for do-match discriminant variables#12666
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This PR fixes spurious unused variable warnings for variables used in non-atomic match discriminants in `do` notation. When `expandNonAtomicDiscrs?` eagerly elaborates discriminants (creating TermInfo for variable references), and the inner match elaboration is postponed, `withTermInfoContext'` in `elabDoElemFns` would detect the postponed mvar result and discard all info subtrees — including the TermInfo that marks discriminant variables as used. The fix wraps the result with `mkSaveInfoAnnotation` (the same mechanism used by `elabLetMVar`) to prevent the info subtrees from being discarded. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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This PR fixes spurious unused variable warnings for variables used in non-atomic match discriminants in
donotation. For example, inmatch Json.parse s >>= fromJson? with, the variableswould be reported as unused.The root cause is that
expandNonAtomicDiscrs?eagerly elaborates the discriminant viaTerm.elabTerm, which creates TermInfo for variable references. The result is then passed toelabDoElemfor further elaboration. When the match elaboration is postponed (e.g. because the discriminant type contains an mvar fromfromJson?), the result is a postponed synthetic mvar. ThewithTermInfoContext'wrapper inelabDoElemFnschecksisTacticOrPostponedHole?on this result, detects a postponed mvar, and replaces the info subtree with aholenode — discarding all the TermInfo that was accumulated during discriminant elaboration.The fix applies
mkSaveInfoAnnotationto the result, which preventsisTacticOrPostponedHole?from recognizing it as a hole. This is the same mechanism thatelabLetMVaruses to preserve info trees when the body is a metavariable.🤖 Generated with Claude Code