Git Blame File: Understanding the Power of Copy Detection

When it comes to understanding the history of changes made to a codebase, Git's blame command is an essential tool. One feature that can be particularly useful in this regard is copy detection using the `-C` option. In this article, we'll explore how to use this option to detect copied code and understand its various nuances.

Enabling Copy Detection

To enable copy detection, you simply need to add the `-C` option to your Git blame command. However, if you want to take it a step further and copy from existing files, you can do so by adding multiple `-C` options. For example, `git blame -C -C file` will search for new code among all the files in the parent commit.

Thresholds and Whitespace Changes

When using the `-C` option, there are two thresholds to consider: one for copy detection and another for move detection. The default threshold for copy detection is 40 characters, while that for move detection is 20 characters. You can override these defaults by appending a number to the `-C` option.

Additionally, the `-w` flag is automatically set when using the `-C` option, which ignores whitespace changes while blaming.

Git GUI Blame

The Git GUI blame command behaves similarly to the command-line version, with one key difference: it can detect code moved or copied from elsewhere in the project. This is due to its default setting of `gui.fastcopyblame`, which enables fast copy detection.

Nuances and Best Practices

While the `-C` option is a powerful tool for detecting copied code, there are some nuances to be aware of. For example, when using multiple `-C` options, Git will search for new code among all the files in the parent commit. When using a single `-C` option, it will look for code blocks that were moved.

To get the most out of this feature, it's essential to read the documentation and understand the thresholds and how they affect your results. You can also use the Git GUI to override the default threshold or set `gui.copyblamethreshold` in your configuration file.

In conclusion, the `-C` option is a valuable tool for understanding the history of changes made to a codebase. By using it effectively, you can identify copied and moved code blocks and gain a deeper understanding of your project's evolution.

Git blame file