fix: add checkSystem calls to hasAssignableMVar#13219
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This PR moves `isLevelMVarAssignable`, `hasAssignableLevelMVar`, and `hasAssignableMVar` from `Lean.MetavarContext` (where they were generic over `[Monad m] [MonadMCtx m]`) to a new `Lean.Meta.HasAssignableMVar` module where they are specialized to `MetaM`. This allows adding `checkSystem` calls in the recursive traversal, enabling cancellation and heartbeat checking during what can be a very expensive operation on large expressions (e.g. category theory proofs with many universe metavariables). All callers were already in `MetaM` or a monad extending it, so the type change is compatible. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Benchmark results for 0e229d7 against 67b6e81 are in. There are no significant changes. @nomeata
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This was referenced Mar 31, 2026
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This PR moves `hasAssignableMVar`, `hasAssignableLevelMVar`, and `isLevelMVarAssignable` from `MetavarContext.lean` to a new `Lean.Meta.HasAssignableMVar` module, changing them from generic `[Monad m] [MonadMCtx m]` functions to `MetaM` functions. This enables adding `checkSystem` calls in the recursive traversal, which ensures cancellation and heartbeat checks happen during what can be a very expensive computation. All callers of these functions were already in `MetaM`, so this change is safe. The motivating case is the `4595_slowdown.lean` test, where `hasAssignableMVar` (with `PersistentHashMap.find?` lookups on `mctx.lDepth`) was the dominant CPU cost during elaboration of category theory definitions. Without `checkSystem` calls, cancellation requests could be delayed by over 2 seconds. The test file `4595_slowdown.lean` gets a slightly increased `maxHeartbeats` limit because `checkSystem` now detects heartbeat exhaustion mid-traversal rather than after the function returns. Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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This PR moves
hasAssignableMVar,hasAssignableLevelMVar, andisLevelMVarAssignablefromMetavarContext.leanto a newLean.Meta.HasAssignableMVarmodule, changing them from generic[Monad m] [MonadMCtx m]functions toMetaMfunctions. This enables addingcheckSystemcalls in the recursive traversal, which ensures cancellation and heartbeat checks happen during what can be a very expensive computation.All callers of these functions were already in
MetaM, so this change is safe. The motivating case is the4595_slowdown.leantest, wherehasAssignableMVar(withPersistentHashMap.find?lookups onmctx.lDepth) was the dominant CPU cost during elaboration of category theory definitions. WithoutcheckSystemcalls, cancellation requests could be delayed by over 2 seconds.The test file
4595_slowdown.leangets a slightly increasedmaxHeartbeatslimit becausecheckSystemnow detects heartbeat exhaustion mid-traversal rather than after the function returns.