Apply `-C` option to git blame for more precise blaming in reorganized files

[azanli]

This applies the -C option to the git blame command which helps to better assign blame in files that've been moved around or otherwise reorganized. Instead of blaming the one who moved the code, we should continuing blaming the original committer for greater detail on the line of code rather than the reorganization history of the code.

From the docs:

-C[num] In addition to -M, detect lines moved or copied from other files that were modified in the same commit. This is useful when you reorganize your program and move code around across files. When this option is given twice, the command additionally looks for copies from other files in the commit that creates the file. When this option is given three times, the command additionally looks for copies from other files in any commit.

[Sertion]

Hey Andy! Thank you for the PR.

I've looked into adding this in the past and decided against it for two reasons: 1) I don't know what performance impact it can have in massive git repositories and 2) I feel like I would need to add a file-path property in the blame message tokens. I don't want to struggle with more weird systems and their infinite quirks.

Do you know what the performance impact would be and have you looked into how the path would need to be rendered in a few different systems?

[Sertion]

I've done some research and it looks like it adds a bit of overhead:

github/git/git $ time git blame builtin/blame.c > /dev/null

real    0m0.418s
user    0m0.328s
sys     0m0.089s
github/git/git $ time git blame -C builtin/blame.c > /dev/null

real    0m0.532s
user    0m0.502s
sys     0m0.030s

github/git/git $ time git blame builtin/commit.c > /dev/null

real    0m0.427s
user    0m0.417s
sys     0m0.010s
github/git/git $ time git blame -C builtin/commit.c > /dev/null

real    0m0.896s
user    0m0.896s
sys     0m0.000s

github/chromium/chromium $ time git blame chrome/browser/browser_about_handler.cc > /dev/null
Blaming lines: 100% (75/75), done.

real    0m23.355s
user    0m22.685s
sys     0m0.670s
github/chromium/chromium $ time git blame -C chrome/browser/browser_about_handler.cc > /dev/null
Blaming lines: 100% (75/75), done.

real    0m29.307s
user    0m28.766s
sys     0m0.541s

It is a bit, but not close to what I expected. Will merge this and make some more changes.