Desktop does not display diff changes after renaming and staging file

Description

I have a small source file. I renamed it, made some changes, and added all my changes to the git index.

In Desktop, I see the rename as I would expect, along with the message “The file was renamed but not changed”. This is incorrect. The file was changed. Once I commit, Desktop updates, then I go look at the commit in the history where it shows the correct thing: the rename and the change. I can do a soft reset to bring my changes back to the index, and I see the bug again. The issue persisted across a restart of the app.

Version

• GitHub Desktop: 1.3.5
• Operating system: OSX 10.13.4

Steps to Reproduce

Use the description and attached information.

Additional Information

Here is the original file:

function forEach(func, iterable) {
  let c = 0;
  for (const item of iterable) {
    const ret = func(item, c++);

    if (ret === false) {
      break;
    }
  }
  return c;
}

export default function curriedForEach(func, iterable) {
  if (!iterable) {
    return iterable => forEach(func, iterable);
  }
  return forEach(func, iterable);
}

Here is the result of git diff HEAD -M for the relevant file:

diff --git a/src/functions/for-each.js b/src/transforms/for-each.js
similarity index 52%
rename from src/functions/for-each.js
rename to src/transforms/for-each.js
index 0bb2948..785740c 100644
--- a/src/functions/for-each.js
+++ b/src/transforms/for-each.js
@@ -10,9 +10,4 @@ function forEach(func, iterable) {
   return c;
 }
 
-export default function curriedForEach(func, iterable) {
-  if (!iterable) {
-    return iterable => forEach(func, iterable);
-  }
-  return forEach(func, iterable);
-}
+export default func => iterable => forEach(func, iterable);

[shiftkey]

I’ve been able to reproduce this, but the resolution for this isn’t quite clear. This is what Desktop currently runs when it diffs a file it knows has been renamed:

git diff --no-ext-diff --patch-with-raw -z --no-color -- [path]

Most of those flags are noise so I’ll call out the differences here:

• typically we’d also add the old path here for a renamed file, like we do for getting the diff in a commit, but that’s not the full resolution
• GitHub Desktop doesn’t pass in HEAD as part of diffing renamed files, for reasons specified in the source

https://github.com/desktop/desktop/blob/2d2e1455893ade496348e909ff0a7b742201c44b/app/src/lib/git/diff.ts#L166-L181

Desktop favours diffing against unstaged changes, but Git doesn’t detect renames until the content is staged, but once you stage the file to show the rename that impacts our ability to diff correctly.

[NickCraver]

I came across this today as well. IMO, GitHub Desktop does not have the correct behavior here. Compare with VS Code:

There is a diff I’m about to push up. That should be indicated in the UI. The difference is indeed that the changes are staged, e.g. git diff outputs nothing for that file, but git diff --staged does show the changes:

diff --git a/tests/RedisConfigs/Sentinel/sentinel-26379.conf b/tests/RedisConfigs/Sentinel/sentinel-26479.conf
similarity index 87%
rename from tests/RedisConfigs/Sentinel/sentinel-26379.conf
rename to tests/RedisConfigs/Sentinel/sentinel-26479.conf
index 6d10f60..a341912 100644
--- a/tests/RedisConfigs/Sentinel/sentinel-26379.conf
+++ b/tests/RedisConfigs/Sentinel/sentinel-26479.conf
@@ -1,4 +1,4 @@
-port 26379
+port 26479
 sentinel monitor mymaster 127.0.0.1 7010 1
 sentinel down-after-milliseconds mymaster 1000
 sentinel failover-timeout mymaster 1000