Vendoring is the moving of all 3rd party items such as plugins, gems and even rails into the /vendor directory. This is one method for ensuring that all files are deployed to the production server the same as the dev environment.
The activity described above, on its own, is fine. It merely describes the deployment location for various resources in an application.
However, many programmers have begun to commit the result of the above procedure to their own source code repositories.
That is to say, they copy all of the files at some version from one version control repository and paste them into a different version control repository.
You should have flinched reading the previous description. This practice is more vile than extending existing code by duplicating whole functions instead of using inheritance and abstraction, and for the same reasons.
Extracting code from a version control repository to be archived in a compressed file or stored in a particular directory for deployment is not bad.
Extracting code from a version control repository to be re-comitted to a different version control repository is evil.
When you copy code between repositories:
- all history, branch, and tag information is lost
- pulling updates is impossible
- it invites modification, divergence, and unintentional forks
- it wastes space
- it is excruciatingly tedious to discover later which version of the code was the canonical source of the copied version, unless the person doing it went out of their way to document that information
Git's submodule mechanism stores a URL and a commit hash in your repository, which itself is under version control.
(TODO: explain more, examples of work-alikes from different VCSs)
If you can't use git submodules, use a script that deploys your third-party resources at the appropriate time, from a canonical source.
(TODO: describe more, provide examples)
If you have a situation where it seems like "vendoring" is really the best way to deploy your code, contact me, call me an idiot, and describe why. I'm sure there's a better way, and where there's not, it's a bug. I hope to eventually document all such situations to prevent people from falling into this bad habit.