Setting up IntelliJ IDEA as Diff and Merge Tool in Fork

idea-fork.md

Setting up IntelliJ IDEA as Diff and Merge Tool in Fork

To configure Fork to use IntelliJ IDEA for diffing and merging, follow the steps below.

---

1. Prerequisites

Ensure you have the command-line launcher idea installed.

• Path: /usr/local/bin/idea
• You can verify this by running which -a idea in your terminal.

---

2. Configure the External Diff Tool

1. Open Fork and go to Preferences / Settings (Cmd + ,).
2. Select the Integration tab.
3. Under External Diff Tool, select Custom... from the dropdown and click Edit... (or click Edit... if already selected).
4. Configure the fields as follows:
   • File Path: /usr/local/bin/idea
   • Arguments: diff $LOCAL $REMOTE
5. Click Edit to save.

---

3. Configure the External Merge Tool

When merging files that were added in both branches independently (where no common base file exists), Fork passes an empty $BASE variable. To prevent IntelliJ IDEA from failing with a "Can't process file" error, we can delegate the merge to a lightweight custom wrapper script.

Setup Instructions

1. Create the wrapper script

Create a file named idea-merge-fork (for example, in /usr/local/bin/idea-merge-fork or any other directory on your $PATH):

#!/bin/sh
if [ -f "$3" ]; then
    /usr/local/bin/idea merge "$1" "$2" "$3" "$4"
else
    /usr/local/bin/idea merge "$1" "$2" "$4"
fi

Make the script executable:

chmod +x /path/to/idea-merge-fork

2. Configure Fork

1. In Fork's Integration tab, under Merge Tool, select Custom... and click Edit....
2. Configure the fields as follows:
   • File Path: /path/to/idea-merge-fork (replace with the absolute path to your script)
   • Arguments: $LOCAL $REMOTE $BASE $MERGED
3. Click Edit to save.

---

4. Verification

Now, whenever you perform a merge conflict resolution or want to view external diffs within Fork, it will launch IntelliJ IDEA with the correct files and UI windows automatically!