tustvold opened a new pull request, #4767:
URL: https://github.com/apache/arrow-datafusion/pull/4767

   # Which issue does this PR close?
   
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   Closes #3437
   Closes #3791
   
   (although these were actually fixed by 
https://github.com/apache/arrow-datafusion/pull/4038)
   
   # Rationale for this change
   
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    Why are you proposing this change? If this is already explained clearly in 
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   Having mutable state associated with `OptimizerConfig` complicates 
implementing it for `SessionState`. I originally hoped to implement 
`OptimizerConfig` for `DataFrame`, but this would have required churning all 
the planning machinery and so I decided against this.  
   
   There is one implication potentially worth highlighting with this change, as 
the state is now associated with the `OptimizerRule` and not an 
`OptimizerContext` created for the call to `SessionState::optimize`, state will 
now bleed across calls whereas it previously wouldn't. In some ways this is 
better, as previously calling `optimize` twice could theoretically result in an 
alias collision, but I thought it worth highlighting.
   
   # What changes are included in this PR?
   
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   There is no need to duplicate the description in the issue here but it is 
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   Move alias state from `OptimizerConfig` onto the individual rules
   
   # Are these changes tested?
   
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   # Are there any user-facing changes?
   
   Yes, queries will get potentially different aliases assigned to them by the 
optimizer.
   
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