Support shallow fetch through net.git-fetch-with-cli

[Ygg01]

What does this PR try to resolve?

Fixes #14956

How should we test and review this PR?

Additional information

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[weihanglo]

I don't think we are using variants other than NoChange/DepthAtRemote. We might just leave then unimplmented!(…).

cargo/src/cargo/sources/git/mod.rs

Lines 35 to 57 in 611b7c4

	pub(crate) fn to_shallow_setting(
	&self,
	repo_is_shallow: bool,
	gctx: &GlobalContext,
	) -> gix::remote::fetch::Shallow {
	let has_feature = |cb: &dyn Fn(GitFeatures) -> bool| {
	gctx.cli_unstable()
	.git
	.map_or(false, |features| cb(features))
	};
	// maintain shallow-ness and keep downloading single commits, or see if we can do shallow clones
	if !repo_is_shallow {
	match self {
	RemoteKind::GitDependency if has_feature(&|features| features.shallow_deps) => {
	}
	RemoteKind::Registry if has_feature(&|features| features.shallow_index) => {}
	_ => return gix::remote::fetch::Shallow::NoChange,
	}
	};
	gix::remote::fetch::Shallow::DepthAtRemote(1.try_into().expect("non-zero"))
	}

[weihanglo]

For test, adding one simple backend test should be good.

cargo/tests/testsuite/git_shallow.rs

Lines 40 to 43 in 3e96f1a

	#[cargo_test]
	fn git2_fetch_complete_dep_two_revs() {
	fetch_dep_two_revs(Backend::Git2, RepoMode::Complete)
	}

I would also encourage to try if we can have cover more gitoxide tests for git CLI with the same switch backend trick.

Also, I'd like to see a test like:

1. First using gix to fetch
2. Compiles.
3. Add a new commit
4. Use git cli to fetch
5. Can still compile.

[Ygg01]

Hm, I tried that with:

https://github.com/rust-lang/cargo/pull/15315/files#diff-bbd634ceb4c39b4119029427e558942d8eeefb1a24f033332bb0a36d73aca890R47-R51

It does not work.

test git_shallow::git_cli_fetch_complete_dep_two_revs ... FAILED

successes:

successes:

failures:

---- git_shallow::git_cli_fetch_complete_dep_two_revs stdout ----
running `C:\projects\cargo\target\debug\cargo.exe check -v -Zgit=shallow-deps`

thread 'git_shallow::git_cli_fetch_complete_dep_two_revs' panicked at tests\testsuite\git_shallow.rs:135:10:

test failed running `C:\projects\cargo\target\debug\cargo.exe check -v -Zgit=shallow-deps`
error: process exited with code 101 (expected 0)
--- stdout

--- stderr
warning: no edition set: defaulting to the 2015 edition while the latest is 2024
    Updating git repository `file:///C:/projects/cargo/target/tmp/cit/t0/meta-dep`
warning: spurious network error (3 tries remaining): shallow fetch is not supported by the local transport; class=Net (12)
warning: spurious network error (2 tries remaining): shallow fetch is not supported by the local transport; class=Net (12)
warning: spurious network error (1 tries remaining): shallow fetch is not supported by the local transport; class=Net (12)
error: failed to get `bar` as a dependency of package `foo v0.0.0 (C:\projects\cargo\target\tmp\cit\t0\foo)`

Caused by:
  failed to load source for dependency `bar`

Caused by:
  Unable to update file:///C:/projects/cargo/target/tmp/cit/t0/meta-dep?rev=a3e80bc72d40dc21a921742d9f808e7be2b3302f

Caused by:
  failed to clone into: C:\projects\cargo\target\tmp\cit\t0\home\.cargo\git\db\meta-dep-356a1674513a4a27-shallow

Caused by:
  network failure seems to have happened
  if a proxy or similar is necessary `net.git-fetch-with-cli` may help here
  https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli

Caused by:
  shallow fetch is not supported by the local transport; class=Net (12)

stack backtrace:
   0: std::panicking::begin_panic_handler
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library\std\src\panicking.rs:692
   1: core::panicking::panic_fmt
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library\core\src\panicking.rs:75
   2: cargo_test_support::panic_error::pe
             at .\crates\cargo-test-support\src\lib.rs:99
   3: cargo_test_support::panic_error<anyhow::Error>
             at .\crates\cargo-test-support\src\lib.rs:91
   4: cargo_test_support::Execs::run
             at .\crates\cargo-test-support\src\lib.rs:1061
   5: testsuite::git_shallow::fetch_dep_two_revs
             at .\tests\testsuite\git_shallow.rs:130
   6: testsuite::git_shallow::git_cli_fetch_complete_dep_two_revs
             at .\tests\testsuite\git_shallow.rs:49
   7: testsuite::git_shallow::git_cli_fetch_complete_dep_two_revs::closure$0
             at .\tests\testsuite\git_shallow.rs:48
   8: core::ops::function::FnOnce::call_once<testsuite::git_shallow::git_cli_fetch_complete_dep_two_revs::closure_env$0,tuple$<> >
             at C:\Users\~~~~~~\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ops\function.rs:250
   9: core::ops::function::FnOnce::call_once
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library\core\src\ops\function.rs:250     
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Should I set the netgit-fetch-with-cli parameter somewhere as well. I'm not sure how the tests work. Is there a guide or something?

[weihanglo]

See the https://doc.crates.io/contrib/tests/index.html and cargo-test-support doc.

You can read how other test works (not limited to git-related tests).
You can also check how switching backend works in git tests. --config override should be able to help set the net.git-fetch-with-cli option.