cargo vendor doesn't re-vendor if the version number hasn't changed

[jsgf]

Problem

cargo vendor fails to re-vendor a package if:

• the package vendor dir has a version number (eg because it's not the most recent, or --versioned-dirs is in use)
• the code has changed

This can happen if the code is coming from a git repo and the rev has been updated, if a patch has been added in the [patch] section of the Cargo.toml, or when switching between crates.io and git as a source.

This doesn't happen for non-versioned directories because cargo vendor unconditionally re-vendors their contents.

Possible Solution(s)
Rather than just comparing the version, it should also check for changes to the patch and/or origin specification.

Notes

Output of cargo version: 1.42, but this hasn't changed in recent versions

[roblabla]

I'm affected by this, switching from a git source to a crates.io published version for a previously unpublished crate.