unified diffs with -U0 show incorrect line number about diff-so-fancy HOT 13 CLOSED

Interesting... this has never come up before. I think most people just roll with the default three lines of context. I made a change on a sample file on line #7, and this is the output from diff:

With three (-u) lines of context the hunk header is: @@ -4,7 +4,7 @@
With two (-U2) lines of context the hunk header is: @@ -5,5 +5,5 @@
With one (-U1) lines of context the hunk header is: @@ -6,3 +6,3 @@
With zero (-U0) lines of context the hunk header is: @@ -7 +7 @@

If you can find for me what those numbers mean I might be able to fix this. diff-so-fancy has no way of knowing how many lines of context diff generated (or even if diff was used), so we can only "guess" based on the input.

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The code in question is this line. If we can find a way to calculate the correct number of context lines there instead of defaulting to three this will be easy.

I don't see an easy way to calculate the offset based on the hunk header though.

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as I understand, those numbers mean:

1. line number of the first line that will be displayed in the hunk
2. (after comma) total number of lines that are displayed in the hunk

so for -U2 the latter would be 2 + 1 + 2 = 5.

however I can't tell you the right algorithm to find the line number for any -U setting.

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oh, maybe just count amount of lines that are prefixed neither with + nor -?

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I'm wondering if it might not be easier to just add a new cli param for d-s-f to specify the number of context lines?

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I'm wondering if it might not be easier to just add a new cli param for d-s-f to specify the number of context lines?

would be fine for the first iteration, but not as convenient to end user :) User would have to invent some sort of helper command like git diffu that would do something like

contextLines=$1
shift
git diff -U$contextLines -c dsf.newOpt=$contextLines $@

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@kambala-decapitator I think I have this working. When I went to write a unit test to capture this new (corrected) output I noticed that three unit tests were failing. Upon closer inspection they were all using -U0 and d-s-f has been reporting the wrong line number the entire time! No one noticed until now.

Can you please test the context-lines branch and see if it works for you?

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@scottchiefbaker from short test this works correctly now! Thanks!

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@kambala-decapitator kick around for a week, see if anything crops off. If you give me the green light after a week I'll merge it.

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I was actively using -U0 today and all line numbers were correct. Same with the default 3 lines.

Will update you in a week.

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@kambala-decapitator it would be helpful if you could test with some other options for -U. I'm 99% most people will us 0 or 3, but it would be good to test with other values as well.

I believe d-s-f should work up to 18 now.

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-U2 shows correct info as well

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I'm gonna merge this branch in to next and it will go live when we release the next version.

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