When `cargo install --git` checks out a commit, also set the branch and tag refs

[tessus]

Problem

Overview

cargo install --git does not retrieve tags or branch info.

My command is: cargo install --git https://github.com/tessus/mvt-cargo.git --branch xyz

So, cargo install fetched the correct branch but renamed it to master and did not fetch any tags either. 🤔

P.S.: Please note that this example is a bit exaggerated. In most cases the most recent tag should match the info in Cargo.toml. I only used it to even more underscore the issue I am seeing.

Details

cargo install

$ cargo install --git https://github.com/tessus/mvt-cargo.git --branch xyz
$ mvt-cargo
Version: 0.1.0-0123b0f4

manual checkout and cargo build/install

$ git clone -b xyz https://github.com/tessus/mvt-cargo.git
$ cd mvt-cargo
$ cargo build --release
$ ./target/release/mvt-cargo
Version: 0.1.1-0123b0f4 (xyz)

Investigation

A cargo install --git https://github.com/tessus/mvt-cargo.git --branch xyz creates a somewhat messed-up git directory in .cargo/git/checkouts/. e.g. repo-7f25bc5356a562d5. I call it messed-up because part of the info is missing (tags) and incorrect (branch).

The binary is then compiled from within this directory. However, in this directory there are no tags from the https://github.com/tessus/mvt-cargo.git repository, nor is the branch name correct.
This is why my build.rs cannot determine a tag nor the correct branch.

In the repo-7f25bc5356a562d5 dir, the following happens:

$ git describe --abbrev=0 --tags
fatal: No names found, cannot describe anything.

$ git rev-parse --abbrev-ref HEAD
master

However, it should show the following (which is also shown when I run these commands in the directory cloned with git clone -b xyz https://github.com/tessus/mvt-cargo.git)

$ git describe --abbrev=0 --tags
0.1.1

$ git rev-parse --abbrev-ref HEAD
xyz

Problem

As you can see, the output is different depending on how the binary was built.
It is currently impossible to use a build.rs script that generates correct information about the git repo, when using cargo install --git ....

Workaround

• clone the repo
• use cargo install --path ./path/to/repo or cargo build (from within the repo)

Proposed Solution

Feature request

Preserve tags and branch info, when using cargo install --git ....

Notes

I am not sure, whether the current behavior is a bug or not. If it is, please let me know and I create a bug report instead.
Otherwise, let's keep this feature request as is.

Link to minimal viable test code: https://github.com/tessus/mvt-cargo/tree/xyz

[epage]

Whether for cargo install or when depending on a package, Cargo always checks out git commits without other context like this, allowing the checkout to be immutable.

Maybe we could consider creating a separate checkout for the purposes of cargo install that would have the branch and tag refs set. It would slow it down though it is a release build so it'll already be slow. This also wouldn't be at parity with registry packages because they don't have a .git directory.

We also have a request in #6583 for setting package.version dynamically though that is more important for registries while this is more of the "marketing" / "product" version

[tessus]

Maybe we could consider creating a separate checkout for the purposes of cargo install that would have the branch and tag refs set.

This would be awesome. 🚀 I hope for the best.

Should this be accepted, I can help coding it... maybe. I am certainly up for trying.
(I am not familiar with the internals of cargo, but if it is just using different options for cloning te repo, it shouldn't be too complicated.)

It would slow it down though it is a release build so it'll already be slow.

Yep, I doubt it would be considerably slower. 🤣