Allows the default git/gitoxide configuration to be obtained from the ENV and config

[linyihai]

What does this PR try to resolve?

The default git/gitoxide feautures config can be obtained througt -Zgit and -Zgitoxide.
However, it cannot be obtained from environment variables or configurations.
It's not very ergonomic.

How should we test and review this PR?

The previous commit explained the staus quo, the next commit addressed the problem.

Additional information

Inspired by #11813 (comment)
See also #13285 (comment)

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[epage]

I assume this is meant to resolve the immediate part of #13688 (leaving aside the more general problem). Is that right?

[epage]

I assume these were chosen to align with GitoxideFeatures::safe() and to mirror if you do -Zgitoxide

However, this breaks down if you do CARGO_UNSTABLE_GITOXIDE_FETCH=true, then almost everything else becomes enabled (we should have a test to show this case).

Some other challenges with these defaults

• Unclear what the motivation is (could have comment pointing to GitoxideFeature::safe)
• Challenge in keeping in sync with GitoxideFeature::safe

Should we instead just default everything to false?

[Nemo157]

What I would love to just work is CARGO_UNSTABLE_GITOXIDE=fetch,list_files and CARGO_UNSTABLE_GITOXIDE=true mirroring the CLI flag (which would also imply you could have unstable.gitoxide = "fetch,list_files" in the config file).

[weihanglo]

Yeah maybe we can make it a comma separated list to reduce the complexity.

Wonder do people really use individual gitoxide features? I always assume that people would just enable them as a whole, though gitoxide author recommends keeping them separately: #13252 (comment).

[linyihai]

What I would love to just work is CARGO_UNSTABLE_GITOXIDE=fetch,list_files and CARGO_UNSTABLE_GITOXIDE=true mirroring the CLI flag (which would also imply you could have unstable.gitoxide = "fetch,list_files" in the config file).

So what we defined as table is going to be replaced with a string? It makes sense, I have no objection to this, but it is not clear that it will break the configuration of the previous version？

[Nemo157]

It's possible to support both, via #[serde(deserialize_with = ...)] and a custom deserializer that handles a string/list or a struct, like

cargo/src/cargo/util/context/mod.rs

Line 2673 in 88d55a8

fn progress_or_string<'de, D>(deserializer: D) -> Result<Option<ProgressConfig>, D::Error>

[bors]

☔ The latest upstream changes (presumably #13696) made this pull request unmergeable. Please resolve the merge conflicts.

[ehuss]

r? weihanglo

[linyihai]

In my new commit, a string can be parsed as git/gitoxide features in ENV and Config.
You can pass 'all' to enable predefined features.

CARGO_UNSABLE_GIT='all' cargo fetch
CARGO_UNSABLE_GIT='shallow-deps' cargo fetch
cargo fetch --config "unstable.git='shallow-deps'"
cargo fetch --config "unstable.git='all'"

In Config, the git/gitoxide can be defined as

# as string
[unstable]
git = 'all'

# still can be defined as table, but all fields needed
[unstable.git]
shallow_deps = true
shallow_index = true

But the defect is that the fields as ENV will be ignored.

CARGO_UNSABLE_GIT_SHALLOW_DEPS CARGO_UNSABLE_GIT_SHALLOW_INDEX cargo fetch

In ENV, it seems that a struct cann't be parser from string and table in the sametime.

[linyihai]

I assume this is meant to resolve the immediate part of #13688 (leaving aside the more general problem). Is that right?

Yes，this tend to mirror the -Zgit/-Zgitoxide as possible.

[weihanglo]

Sorry for the late review 🙇🏾‍♂️

[weihanglo]

While this seems fine for now, I am a bit worried about the change.

What about having an enum deriving serde?

#[derive(Debug, Copy, Clone, Default, Deserialize)]
#[serde(untagged)]
pub enum Gitoxide {
    #[default]
    All,
    Some(GitoxideFeatures),
}

so that I assumed it would work well with

[unstable]
gitoxide = true

# or
[unstable.gitoxide]
checkout = true

As well as enviroment variables?

CARGO_UNSTABLE_GITOXIDE=true
CARGO_UNSTABLE_GITOXIDE_CHECKOUT=true

[linyihai]

It doesn't seem to be working. see gitoxide_features_as_table in the lastest commit.