Re: [PATCH 6/6] t4124: fix test for non-compliance diff

> On Thu, Mar 19, 2020 at 09:00:07PM +0700, Đoàn Trần Công Danh wrote:
> 
> > POSIX's diff(1) requires output in normal diff format.
> > However, busybox's diff's output is written in unified format.
> 
> That's a pretty big difference. I'm surprised this only produces one
> problem in the test scripts. ;)
> 
> > POSIX requires no option for normal-diff format.
> > 
> > A hint in test-lib-functions::test_cmp said `diff -u` isn't available
> > everywhere.
> > 
> > Workaround this problem by assuming `diff(1)` output is unified
> > if we couldn't make anything from normal-diff format.
> 
> I wonder if we could use "git diff" here. We have to be careful about
> circular reasoning in our tests (i.e., making sure we're not verifying
> output with the same code that we're testing), but I think here we're
> checking how "apply --whitespace=fix" works.
> 
> But if this is the only spot, then adjusting to handle unified or normal
> diff isn't too bad.
> 
> > diff --git a/t/t4124-apply-ws-rule.sh b/t/t4124-apply-ws-rule.sh
> > index 971a5a7512..2a54ce96b5 100755
> > --- a/t/t4124-apply-ws-rule.sh
> > +++ b/t/t4124-apply-ws-rule.sh
> > @@ -52,6 +52,12 @@ test_fix () {
> >  
> >  	# find touched lines
> >  	$DIFF file target | sed -n -e "s/^> //p" >fixed
> > +	if ! test -s fixed; then
> > +		$DIFF file target |
> > +		grep '^+' |
> > +		grep -v '^+++' |
> > +		sed -e "s/+//" >fixed
> > +	fi
> 
> I think those greps could be lumped into sed like:
> 
>   sed -ne "s/^+[^+]//p"
> 
> (at the cost of missing blank lines, but I think that's OK for our
> purposes here; it could be fixed with an ERE).
> 
> Could we then make a single invocation that covers both diff formats? We
> can further observe that the only thing we do with the "fixed" file is
> count the lines, so we can leave the markers. Which means we could ditch
> sed entirely and use grep. Something like:
> 
> diff --git a/t/t4124-apply-ws-rule.sh b/t/t4124-apply-ws-rule.sh
> index 971a5a7512..15cb0c81b7 100755
> --- a/t/t4124-apply-ws-rule.sh
> +++ b/t/t4124-apply-ws-rule.sh
> @@ -50,8 +50,9 @@ test_fix () {
>  	# fix should not barf
>  	apply_patch --whitespace=fix || return 1
>  
> -	# find touched lines
> -	$DIFF file target | sed -n -e "s/^> //p" >fixed
> +	# find touched lines; handle either normal or unified
> +	# diff, as system diff may generate either
> +	$DIFF file target | grep '^[>+][^+]' >fixed
>  
>  	# the changed lines are all expected to change
>  	fixed_cnt=$(wc -l <fixed)
> 
> seems to work for with both busybox diff and GNU diff.