[PATCH] D133052: [clang] Avoid crash when expanding conversion templates in concepts.

[Utkarsh Saxena via Phabricator via cfe-commits]

usaxena95 added a comment.

My suggestion would be to properly handle cycles in `CheckConstraintSatisfaction`. This problem goes beyond cycles introduced by conversion. See #53213 <https://github.com/llvm/llvm-project/issues/53213> and #44304 <https://github.com/llvm/llvm-project/issues/44304> https://godbolt.org/z/v41ez6eW4. These two bugs are due to an assertion failure while inserting entry into SatisfactionCache.

My suggestion would be detect cycles in `CheckConstraintSatisfaction`. We already have a way to check "whether we have seen this before ?" in `SatisfactionCache` using `FoldingSet` for `ConstraintSatisfaction`. We could use a similar set to track the constraints being evaluated. Stop evaluation when we detect a cycle. Attach appropriate details to the Satisfaction and fail the constraint.


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