fix: handle file mode changes (old mode/new mode) in diff parsing

[jkoppel]

Summary

Files with old mode/new mode extended headers (e.g. chmod +x changes) are not parsed correctly, causing two bugs:

1. new mode lines are not recognized as extended headers. The ExtendedHeader constants include Old: 'old' which matches old mode ..., but only have NewFile: 'new file' for new-prefixed headers. Since 'new mode ...' does not start with 'new file', parseExtendedHeader returns null, breaking the extended header loop prematurely.

2. All subsequent files are dropped. When parseFileChange returns undefined (due to unrecognized headers and no matching return conditions), parseFileChanges uses break instead of advancing past the problematic entry, causing ALL subsequent files in the diff to be silently dropped.

Reproduction

import parseGitDiff from 'parse-git-diff';

// Mode-only change
const diff1 = `diff --git a/script.sh b/script.sh
old mode 100644
new mode 100755`;

console.log(parseGitDiff(diff1).files); // [] — expected 1 file

// Mode change followed by another file
const diff2 = `diff --git a/script.sh b/script.sh
old mode 100644
new mode 100755
diff --git a/readme.md b/readme.md
index abc1234..def5678 100644
--- a/readme.md
+++ b/readme.md
@@ -1 +1 @@
-old
+new`;

console.log(parseGitDiff(diff2).files); // [] — expected 2 files

Fix

• Add NewMode: 'new mode' to ExtendedHeader constants so new mode lines are properly recognized
• Add a fallback return in parseFileChange for files that have only extended headers (like mode changes) but no ---/+++ markers or chunks — returns a ChangedFile with the path from the comparison input line
• Change parseFileChanges to skip unparseable entries (continue) instead of aborting the entire parse (break), so one unparseable file doesn't cause all subsequent files to be lost

Tests

Added 3 new test cases:

• Mode-only change (old mode 100644 → new mode 100755)
• Mode change with content changes
• Mode change followed by another file (verifies subsequent files are not dropped)

All existing tests continue to pass.

[yeonjuan]

@jkoppel Hello, thank you. This project has not been properly handling old mode and new mode. I think it would be good to output the changes in old and new mode as part of the parse results. What do you think? I created a PR to address this issue based on your commit.

• https://github.com/jkoppel/parse-git-diff/pull/1

[jkoppel]

Sounds like a great idea @yeonjuan !

[yeonjuan]

LGTM