Hunk keeps showing as modified when an LF (0a) character is added after a write

[patenteng]

If you replace an existing file in a Git repository with the same file but without an LF character at the end of file, the last line will correctly show as modified. However, once you save the file in Vim an LF character is added at the end. Nevertheless, the hunk still indicates that the last line is modified until you reload the file.

To reproduce first create the Git repository with a test file.

mkdir test
cd test
git init
echo "test" > test
git add test
git commit -m "Test"

As you can see, there is an LF (0a) at the end of file.

❯ hexdump -C test
00000000  74 65 73 74 0a                                    |test.|
00000005

Now remove the LF with vim.

vim -b test
:set noeol
:wq

The LF character is now removed and the line is correctly shown as modified.

❯ hexdump -C test
00000000  74 65 73 74                                       |test|
00000004
❯ git diff
diff --git a/test b/test
index 9daeafb..30d74d2 100644
--- a/test
+++ b/test
@@ -1 +1 @@
-test
+test
\ No newline at end of file

Open the file in Vim.

vim test

Save it in order to insert the LF character.

:w

As you can see, the 0a character has been inserted making the line 5B long instead of the 4B when the file was opened.

❯ hexdump -C test
00000000  74 65 73 74 0a                                    |test.|
00000005

However, the hunk still indicates that the line is modified. Reloading the file fixes the issue.

:e test

[airblade]

This is because when you open the file-without-EOL in text mode, i.e. not binary mode, and then write it to add an EOL, Vim doesn't increment the change counter (b:changedtick) – and gitgutter uses this variable to know when the file has changed, so that it can run only when there have been changes.

vim-gitgutter/autoload/gitgutter/diff.vim

Lines 417 to 419 in 85ca3a0

	function! s:save_last_seen_change(bufnr) abort
	call gitgutter#utility#setbufvar(a:bufnr, 'tick', getbufvar(a:bufnr, 'changedtick'))
	endfunction

vim-gitgutter/autoload/gitgutter.vim

Lines 190 to 192 in 85ca3a0

	function! s:has_fresh_changes(bufnr) abort
	return getbufvar(a:bufnr, 'changedtick') != gitgutter#utility#getbufvar(a:bufnr, 'tick')
	endfunction

I'm not sure what gitgutter could do about this; it seems like a bug in b:changedtick.