GitSigns: Script breaks when the first anchor line is too long for `git diff` output

[mihawk90]

OK so I've been using this script for the last couple days with no issues (and it's been a great help), but yesterday I ran into a problem where it was convinced that I didn't save my file and/or I was opening the wrong file or.. whatever, anyway, it was throwing this in my face:

Diff didn't match the subtitles! Make sure to save your file.

However, I could see actual git diff output, so that wasn't the issue. This git diff command ran locally:

arch1t3cht-Aegisub-Scripts/macros/arch.GitSigns.moon

Line 54 in 4f5ba08

handle = io.popen("#{get_git()} -C \"#{dir}\" diff --raw -p \"#{ref}\" \"#{aegisub.file_name()}\"")

outputs this:

:100644 100644 7f46be0 0000000 M        433/[AntBnecn] Naruto Shippuuden - 433 [720p] [29377B9D].ass

diff --git a/433/[AntBnecn] Naruto Shippuuden - 433 [720p] [29377B9D].ass b/433/[AntBnecn] Naruto Shippuuden - 433 [720p] [29377B9D].ass
index 7f46be0..cf7f8ff 100644
--- a/433/[AntBnecn] Naruto Shippuuden - 433 [720p] [29377B9D].ass      
+++ b/433/[AntBnecn] Naruto Shippuuden - 433 [720p] [29377B9D].ass      
@@ -80,8 +80,8 @@ Comment: 1,0:01:11.08,0:01:12.07,ED35 Romaji3,,0,0,0,karaoke,{\fad(300,200)}{\k3
 Comment: 1,0:01:12.07,0:01:20.32,ED35 Romaji,,0,0,0,karaoke,{\fad(300,200)}{\k14}a{\k19}{\k24}o{\k19}zo{\k19}ra {\k19}no {\k19}ha{\k19}te {\k19}ma{\k168}de {\fad(300,200)}{\k19}to{\k19}ba{\k19}shi{\k44}te {\k34}yu{\k317}ke
 Dialogue: 0,0:00:04.00,0:00:05.96,Default,,0,0,0,,This...can't be.
 Dialogue: 0,0:00:06.50,0:00:07.87,Default,,0,0,0,,What is happening?!
-Dialogue: 0,0:01:04.12,0:01:05.33,Default,,0,0,0,,{\i1}Right around then,{\i0}
-Dialogue: 0,0:01:05.46,0:01:08.16,Default,,0,0,0,,{\i1}the young shinobi{\i0} {\i1}who just became genin,{\i0}
+Dialogue: 0,0:01:04.12,0:01:05.45,Default,,0,0,0,,{\i1}Right around then,{\i0}
+Dialogue: 0,0:01:05.45,0:01:08.16,Default,,0,0,0,,{\i1}the young shinobi{\i0} {\i1}who just became genin,{\i0}
 Dialogue: 0,0:01:08.87,0:01:13.16,Default,,0,0,0,,{\i1}made their way to a village{\i0} {\i1}that had lost their Jōnin.{\i0}
 Dialogue: 0,0:01:14.83,0:01:19.62,Default,,0,0,0,,{\i1}Amongst them was{\i0} {\i1}the Child of Prophecy...Naruto.{\i0}
 Dialogue: 1,0:01:37.32,0:01:47.92,OP18 Eng,,0,0,0,,{\blur0.5}Throwing out a single excuse that, "It's finally nice outside!"
@@ -92,282 +92,282 @@ Dialogue: 1,0:01:59.55,0:02:10.15,OP18 Eng,,0,0,0,,{\blur0.5}My destination is s
…

Luckily that error message is only output in one place:

arch1t3cht-Aegisub-Scripts/macros/arch.GitSigns.moon

Lines 140 to 142 in 4f5ba08

	if offset == nil
	aegisub.log("Diff didn't match the subtitles! Make sure to save your file.\n")
	aegisub.cancel()

And so I went ahead and added some debug output:

--- arch.GitSigns.moon.orig     2025-07-06 19:18:53.608717043 +0200
+++ arch.GitSigns.moon  2025-07-06 19:19:29.782803540 +0200
@@ -125,13 +125,22 @@
 
     local offset
     for i, section in ipairs(sections)
+        aegisub.debug.out("section for loop #{i}\n")
         for {:newindex, :gline} in *iterate_diff_section(section.lines)
+            aegisub.debug.out('newindex for loop\n')
             if newindex > 1 and gline\match("^%+?Dialogue: ") or gline\match("^%+?Comment: ")
+                aegisub.debug.out('newindex > 1\n')
                 rl = gline\gsub("^%+", "")\gsub("\r$", "")
 
                 aegisub.log(5, "Trying to find anchor line #{gl}\n")
 
                 for si, s in ipairs(subs)
+                    aegisub.debug.out("subs for loop #{si}\n")
+                    aegisub.debug.out("s.raw: #{s.raw}\n")
+                    aegisub.debug.out("rl: #{rl}\n")
+                    aegisub.debug.out("section.newfrom: #{section.newfrom}\n")
+                    aegisub.debug.out("newindex: #{newindex}\n")
+
                     if s.raw == rl
                         offset = si - (section.newfrom + newindex - 1)
                         aegisub.log(5, "Found offset #{offset}")

Sifting through the output I eventually found the right line that would have to match:

section.newfrom: 80
newindex: 1
subs for loop 72
s.raw: Comment: 1,0:01:11.08,0:01:12.07,ED35 Romaji3,,0,0,0,karaoke,{\fad(300,200)}{\k39}GO {\k49}GO
rl: Comment: 1,0:01:11.08,0:01:12.07,ED35 Romaji3,,0,0,0,karaoke,{\fad(300,200)}{\k3

So the problem seems to be that the condition on L135 here fails:

arch1t3cht-Aegisub-Scripts/macros/arch.GitSigns.moon

Lines 134 to 138 in 4f5ba08

	for si, s in ipairs(subs)
	if s.raw == rl
	offset = si - (section.newfrom + newindex - 1)
	aegisub.log(5, "Found offset #{offset}")
	break

Which makes sense because git diff shortens the line, so it's not == the original line.

I'm not entirely sure how to work around this though. Of course string.find() is an option but I see a problem there when only later parts of the line (after git's cut-off) differ.

In the git man page I can't find any way to turn this shortening behaviour off. Even the --word-diff=porcelain still does this :/
So I think the only way to do this would be doing string.find() to find the anchor/offset, but then also check each individual removed line on whether or not it matches the lines in the script :/