Thanks again for your changes. Please address the following suggestions (more detailed explanation below):

• Check for new option in lightline#gitdiff#write_calculation_to_cache() (to support all algorithms)
• Always return added, deleted and modified lines in lightline#gitdiff#algorithms#word_diff_porcelain#calculate
• Add unit tests for show_empty_indicators

You only adapted algorithm word_diff_porcelain. There is another one called numstat in the same directory here:

So instead of checking for the option in word_diff_porcelain only, I would suggest checking between the following two expressions:

This way we can guarantee that all current and all future algorithms will be supported.

This also requires changing word_diff_porcelain to always return added, deleted and modified lines -- even if there are none -- here

Please add additional unit tests that ensure that show_empty_indicators works as expected.

Would you mind adding these suggestions? This is quite a lot and I'm already very thankful for your contribution. Please tell me if you need any help.

I'm sorry, this needs further changes. I you want to, you can open your branch so I can commit there directly. Otherwise feel free to apply and change the provided diffs.

Don't hesitate to ask further questions. At the moment I don't have a lot of time to spend on this plugin but I will answer eventually. 🙂

And we would also need these additional changes to the other algorithm that is provided:

diff --git a/autoload/lightline/gitdiff/algorithms/numstat.vim b/autoload/lightline/gitdiff/algorithms/numstat.vim
index 4fed527..ae665c3 100644
--- a/autoload/lightline/gitdiff/algorithms/numstat.vim
+++ b/autoload/lightline/gitdiff/algorithms/numstat.vim
@@ -17,17 +17,5 @@ function! lightline#gitdiff#algorithms#numstat#calculate(buffer) abort
     return {}
   endif
 
-  let l:ret = {}
-
-  " lines added
-  if l:stats[0] !=# '0'
-    let l:ret['A'] = l:stats[0]
-  endif
-
-  " lines deleted
-  if l:stats[1] !=# '0'
-    let l:ret['D'] = l:stats[1]
-  endif
-
-  return l:ret
+  return { 'A': l:stats[0], 'D': l:stats[1] }
 endfunction

g:LightlineGitDiffAlgorithm makes much more sense. And thanks a lot for providing the unit tests. Your contribution greatly improves the quality of the plugin!