change definitely unproductive cycles to error #137314
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A cycle was previously coinductive if all steps were coinductive. Change this to instead considerm cycles to be coinductive if they step through at least one where-bound of an impl of a coinductive trait goal.
they don't detect any bugs in the search graph. We instead check for these via `search_graph_fuzz`.
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This was referenced Feb 20, 2025
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☔ The latest upstream changes (presumably #137466) made this pull request unmergeable. Please resolve the merge conflicts. |
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builds on top of #136824 by adding a third variant to
PathKindfor paths which may change to be coinductive in the future but must not be so right now. Most notably, impl where-clauses of not yet coinductive traits.With this, we can change cycles which are definitely unproductive to a proper error. This fixes rust-lang/trait-system-refactor-initiative#114
TODO 🤔
Inductiveactually all are as changing them later will be breaking and it can even be unsound if encountered in coherencer? @compiler-errors @nikomatsakis