How does the git diff –pickaxe-all option work, and when might it be useful?

The --pickaxe-all option in git diff is associated with the -S or -G options and is used to identify differences between commits in your Git repository. The -S option is also known as the pickaxe option.

Let’s break it down:

  1. Pickaxe (-S) option: The -S<string> option in git diff will look for commits where the number of occurrences of the specified string has changed. This can be useful when you are trying to find when a particular line of code or string was added or removed.
  2. --pickaxe-all option: The --pickaxe-all option, when used in combination with the -S option, does not stop at showing the first commit that introduced or removed the string. Instead, it will show all the changes from the commit that introduced the change and the changes in every file in that commit, not just the ones that contain the pickaxe string.

Let’s use a concrete example for better understanding:

Imagine you have a codebase and you’ve modified a function foo(). Now, this function is present in multiple files, say file1.cpp and file2.cpp. You modify this function in both files in a single commit. After a while, you realize something broke and you suspect the issue might be related to changes to the foo() function.

In such a situation, you could use git diff -S'foo()' to find the commits where the foo() function was modified. However, this will only show you the differences for the files where foo() was added or removed.

To see all the changes that came with the commits where foo() was modified, you’d use git diff -S'foo()' --pickaxe-all. This will show you the full diff of the commit, not just the diff for the lines that contain foo(). It helps you understand the broader context of the changes that accompanied the modification of the foo() function.

So, the --pickaxe-all option is particularly useful when you’re trying to track the impact of a specific change across a commit, including changes that are not directly related to the string you’re searching for, but might provide additional context for the changes.

Remember that the -S or -G options are necessary for --pickaxe-all to work. Without them, Git will not recognize --pickaxe-all as a valid option.