@swissspidy What tests would you need for this change? You can verify it with the following commands:

(COMP_LINE='wp search-replace --report'; wp cli completions --line="$COMP_LINE" --point=${#COMP_LINE})

produces

--report 
--report-changed-only

preserving the current word. Repeating the word, e.g.

(COMP_LINE='wp search-replace --report --report'; wp cli completions --line="$COMP_LINE" --point=${#COMP_LINE})

produces only

which demonstrates that this change preserves the existing "don't complete options that have already been typed" behaviour. The $assoc_args could be named bit better if this is its only purpose.