Shows changed file as new in diff after permissions update

[Piturnah]

Describe the bug

I checked out DCoxshall/dylstatus@b317670 and made a change resulting in the following diff to main.py:

diff --git a/main.py b/main.py
old mode 100644
new mode 100755
index b597543..ed2fbc3
--- a/main.py
+++ b/main.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 import time
 from io import StringIO
 import sys

$ gex correctly lists the file under "Unstaged changes":

However, instead of listing the correct diff, when expanded it treats the file as though it was a new file. This is almost certainly a bug in src/parse.rs.

gex/src/parse.rs

Line 20 in fcd6818

let diff: IResult<&str, &str> = tag("+++ b/")(diff.get(2).unwrap_or(&""));

Additional context

$ gex --version
gex 0.3.7-dev (fcd6818e126b3c76df319cff8e6f05aa833a159f)

[Piturnah]

After further investigation I have realised this was caused by using $ chmod +x main.py to add executable permissions. Without running this command, the diff produced by git looks like:

diff --git a/main.py b/main.py
index b597543..ed2fbc3 100644
--- a/main.py
+++ b/main.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 import time
 from io import StringIO
 import sys

This should be easy to fix by ignoring the following lines in parsing:

old mode 100644
new mode 100755

But ideally they should be displayed somehow in the diff.

Current gex output:

[Piturnah]

We could try treating the mode change as similarly to a "hunk", as its own optional field in the file diff. I will look at how Magit displays it.