Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
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Sebastian Graf cdbed919ec
fix: preserve TermInfo for do-match discriminant variables (#12666)
This PR fixes spurious unused variable warnings for variables used in
non-atomic match discriminants in `do` notation. For example, in `match
Json.parse s >>= fromJson? with`, the variable `s` would be reported as
unused.

The root cause is that `expandNonAtomicDiscrs?` eagerly elaborates the
discriminant via `Term.elabTerm`, which creates TermInfo for variable
references. The result is then passed to `elabDoElem` for further
elaboration. When the match elaboration is postponed (e.g. because the
discriminant type contains an mvar from `fromJson?`), the result is a
postponed synthetic mvar. The `withTermInfoContext'` wrapper in
`elabDoElemFns` checks `isTacticOrPostponedHole?` on this result,
detects a postponed mvar, and replaces the info subtree with a `hole`
node — discarding all the TermInfo that was accumulated during
discriminant elaboration.

The fix applies `mkSaveInfoAnnotation` to the result, which prevents
`isTacticOrPostponedHole?` from recognizing it as a hole. This is the
same mechanism that `elabLetMVar` uses to preserve info trees when the
body is a metavariable.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-23 23:54:17 +00:00
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src fix: preserve TermInfo for do-match discriminant variables (#12666) 2026-02-23 23:54:17 +00:00
stage0 fix: preserve TermInfo for do-match discriminant variables (#12666) 2026-02-23 23:54:17 +00:00
tests fix: preserve TermInfo for do-match discriminant variables (#12666) 2026-02-23 23:54:17 +00:00
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