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Just signed the CLA.

CLAs look good, thanks!

This is actually wrong, and I don't think I'm familiar enough with vimscript to fix it. Specifically, yapf returns error code 2 if the error is changed, which means I have to catch the ShellError exception, then check if the error code is 2, and do the same formatting logic as in the try. Something like

 try
 let l:result = maktaba#syscall#Create(l:cmd).WithStdin(l:input).Call()
 catch /ERROR(ShellError):/
 if v:shell_error == -1
 call maktaba#error#Shout('Error formatting file: %s', v:exception)
 endif
 endtry
 let l:formatted = split(l:result.stdout, "\n")
 call maktaba#buffer#Overwrite(1, line('$'), l:formatted)

doesn't work since l:result is scoped to within the try block... I don't know how to declare result to have scope outside the try block in vimscript.

Update: for now, I just got rid of the try catch and checked the v:shell_error variable manually.

Does this look good? I've been using it for the past few days and it seems to work fine.

Yep, looks good. Thanks!