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IMPORTANT NOTE:
although this page has a "gitolite.com" URL, this is not about gitolite.
That's just an artifact of "sitaramc.github.com" being translated to
"gitolite.com" and so ALL my git related stuff gets carried over.
Gitolite documentation has another /gitolite in the URL, so
you can tell. My apologies for this confusion.
Git tracks content, not files. As a result, the git blame and the git gui blame commands can detect code moved or copied from elsewhere in the project. It’s a very powerful feature, accessed by specifying the -C flag one or more times, but there are some nuances.
When the -C flag is given only once, it looks for code blocks that were moved. That is, it searches for new code among other files that were also modified in the same commit. This runs very fast.
When you give the flag twice, it looks for new code among all the files in the parent commit, and so it detects code that was copied.
git gui blame behaves like -C -C by default, but can behave like -C if gui.fastcopyblame is true. (In addition, it also appears to set -w, to ignore whitespace changes while blaming).
There is a concept of a “threshold”, which is the minimum number of alphanumeric characters required to count something as a code move/copy – be sure to read under -C in man git-blame.
This threshold defaults to 40 characters for copy detection, and 20 for move detection. You can override it by appending a number to the -C option.
git gui blame defaults to 40 for this – it actually sets -C40 and calls (I assume) the command line blame tool. If you want to override it, use the GUI (Edit->Options), or directly set the gui.copyblamethreshold config variable.
The documentation does not seem to be very clear about the effect of three -C options on git blame. (In the GUI this is done by choosing full copy detection from the right click menu).
The best hint is in builtin-blame.c, which says, within a function called blame_copy_callback:
/*
* -C enables copy from removed files;
* -C -C enables copy from existing files, but only
* when blaming a new file;
* -C -C -C enables copy from existing files for
* everybody
*/Sidenote: correlating the single and double cases in the code with the documentation, I imagine “removed files” actually means “code from some other modified file in the same commit”, and similarly “existing files” means “code from any files in the parent commit”.
-C flags were supplied