fix #26453, require obviously-concrete lower bound for a var to be diagonal #26567
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* origin/master: A few more #26670 fixes (#26773) Revert "deprecate using the value of `.=`. fixes #25954" (#26754) change dim arguments for `diff` and `unique` to keyword args (#26776) reorder pmap arguments to allow do-block syntax (#26783) correct deprecated parametric method syntax (#26789) [NewOptimizer] handle new IR nodes correctly in binary format [NewOptimizer] support line number emission from new IR format fix #26453, require obviously-concrete lower bound for a var to be diagonal (#26567) fix #26743, spurious `return` path in try-finally in tail position (#26753) Also lift SelectInst addrspaces
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This changes method applicability, but is only very slightly breaking, since vars whose lower bounds are other vars are pretty rare in method signatures. Also in such methods the resulting static parameters tend to be undefined, since there is no unique value for them.
Overall I think this makes subtyping a bit more intuitive. Here, I chose to make a var non-diagonal if its lower bound is another var. A possible variation is to make it diagonal if the lower bound var itself has a concrete upper bound (e.g. in
S<:Int, T>:S,Tcould still be diagonal).