fix(git)!: Default to net.git-fetch-with-cli if git is present by epage · Pull Request #17329 · rust-lang/cargo

epage · 2026-08-06T22:15:53Z

What does this PR try to resolve?

This changes the default for how we fetch to use the git CLI if present for better conformity and performance without breaking people (yet) who don't have it.

Part of #17227

How to test and review this PR?

I have triaged open issues related to git-fetch-with-cli.

corrupt_git.rs is an interesting case. From what an agent told me that sounds reasonable, we hit an infinite loop in libgit2. We should report that but not feeling it is bad enough to be a blocker for merging this, especially since people are using a sparse index.

Future goals:

Remove git2 fetch to unblock moving off of curl
Remove git2 to speed up startup and reduce C deps

Future steps:

Add future-incompat when the default falls back to git2
Remove the git check, always defaulting to git-cli
Remove git2 fetch

rustbot · 2026-08-06T22:15:59Z

r? @weihanglo

rustbot has assigned @weihanglo.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: @epage, @weihanglo
@epage, @weihanglo expanded to epage, weihanglo

weihanglo · 2026-08-13T03:52:48Z

corrupt_git.rs is an interesting case. From what an agent told me that sounds reasonable, we hit an infinite loop in libgit2. We should report that but not feeling it is bad enough to be a blocker for merging this, especially since people are using a sparse index.

A possible upstream fix: libgit2/libgit2#7346

weihanglo · 2026-08-16T16:44:15Z

 }

+fn is_git_cli_present() -> bool {
+    #[tracing::instrument(skip_all)]


I think before making it default, we may want to make sure:

What the minimum required Git CLI version we depend on.

This doesn't need to be precise, but at least we figure out an approximate.

What Git CLI v3 would ship and whether it would be hard to keep our compatibility story: https://git-scm.com/docs/BreakingChanges#_git_3_0.

Looked over the proposed change, refutable and sha256 may require a bit more attention, as old Git may not be able to read the new index format.

If there is any more defaults we need to make explicit and opt-out, it is better to as early as possible. (e.g. safe.bareRepository though we already set GIT_DIR explicitly for fetch in git-fetch-with-cli: Set GIT_DIR for bare repository compatibility #14860).

View changes since the review

Made this: #17370

We have Git version detection in #17400.

What the minimum required Git CLI version we depend on.

Just for curiousity I wanted to know, why can't we simply assume the current version(available on user device) to be the appropriate version and if while doing the action we encounter an error, rust's awesome error handling will explain the error to user and may be add a sugestion to upgrade git CLI?
This way If I am using a old unix system with no sudo privilege (like my college HPC server) and cargo needs git pull that could be done by any version, I will not be blocked! Basically it give highest flexibility.

Because that may fail previous-successful builds. To provide a good diagnostic we also need to know what version user need to upgrade to.

For the change to sha256, the change is for the default for git init. Cargo uses ligit2 instead of git init, so we won't be impacted by the hasher default changing with git v3.

### What does this PR try to resolve? Git v3 will enforce `safe.bareRepository=explicit`, while older versions don't. See <https://git-scm.com/docs/BreakingChanges/2.55.0#_git_3_0> This ensures `git gc` work with `safe.bareRepository=explicit` by setting an explicit `GIT_DIR` environment variable. This is not a requirement of making CLI fetch the default, but better to have before Git CLI v3 is out. CC rust-lang#17329 ### How to test and review this PR? You can basically repro this manually today with Git 2.38.0 and later (which `safe.bareRepository` first appears). 1. Set `safe.bareRepository=explicit` 2. `cargo fetch` with config `net.git-fetch-with-cli=true` 3. Put a marker file inside `$CARGO_HOME/git/db/<git-dir>/` 4. `cargo update` to force a git fetch 5. Observe the marker is gone, because Cargo reinitialized the entire db. I am not sure if there is a better way to test it than a marker file though. 🤖 **LLM disclosure**: I told Codex to check if Cargo's `git fetch` usage is not compatibility with Git CLI v3, and surprisingly it told me `git gc` is not good. I didn't expect this.

…7400) ### What does this PR try to resolve? Trying to make the output cleaner, particularly on ambiguous refs, in prep for rust-lang#17329 ### How to test and review this PR? Since progress does not have end-to-end tests, I ran ``` cargo new git-dep cd git-dep cargo add cargo --git https://github.com/rust-lang/cargo/ rm -rf ~/.cargo/git CARGO_NET_GIT_FETCH_WITH_CLI=true nargo check ``` Remaining git output is: ``` remote: Enumerating objects: 187021, done. remote: Counting objects: 100% (326/326), done. remote: Compressing objects: 100% (155/155), done. remote: Total 187021 (delta 241), reused 177 (delta 171), pack-reused 186695 (from 3) Receiving objects: 100% (187021/187021), 69.48 MiB | 4.90 MiB/s, done. Resolving deltas: 100% (130194/130194), done. ```

If we get rid of ligit2 fetch, we'll need to re-evaluate how we do retry testing.

weihanglo · 2026-09-03T19:39:24Z

@rfcbot fcp merge

This proposes changing Cargo default backend for network Git fetches.

Before this

When net.git-fetch-with-cli is unset, Cargo uses the builtin backend (libgit2 as of 1.100-nightly)
net.git-fetch-with-cli=true to opt-in Git CLI for fetches.

After this

When net.git-fetch-with-cli is unset, Cargo uses Git CLI by default, and falls back to the builtin backend if the Git CLI is not present.
net.git-fetch-with-cli=false to switch back to the builtin backend.

This affects both fetching git dependencies and Git registry index, and only network fetching. Repo checkout is still run on libgit2.

Benefits

Address long-standing fetch issue like proxies or SSH authentication that libgit2 doesn't support well.
Git CLI is performant, and doesn't need to pay for startup loading cost if not used (this was already partially addressed outside this switch)
Reduce the support burden on chasing extra Git configuration supports in upstream libgit2
Git CLI is the reference implementation and used by most Git users
See Migrate to CLI git fetching #17227 for more
Eventually like the PR description has said, we may be able to remove away libgit2 C dep from Cargo.

Downsides

Cargo now relies on external tools, and fetches behavior may vary on different systems, user configs, and PATH env vars
- The expectation is that most dev machines has Git installed, and we also added Git CLI version detection. We can also unset more user configs that may impact on fetch behavior.
Due to the lack of programmable output, Git CLI diagnostics slightly regresses, and could be more verbose when --verbose flag is present.
With Git CLI, git fetches now doesn't retry for non HTTP 429 transient errors. Previously libgit2 retries 3 times for both network and spurious errors.

rust-rfcbot · 2026-09-03T19:39:27Z

@weihanglo has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

weihanglo · 2026-09-03T19:42:27Z

+    let result = if gctx
+        .net_config()?
+        .git_fetch_with_cli
+        .unwrap_or_else(|| git_version().is_some())


We should also update doc for net.git-fetch-with-cli.

View changes since the review

Thanks for catching that!

Not specific to this PR, though there is a catch: cargo config get doesn't really reflect the if something then true else false logic. I don't think this is a blocker though worth some thinking.

Tracked in #9301

arlosi · 2026-09-03T19:50:48Z

@@ -1,7 +1,7 @@
-<svg width="740px" height="92px" xmlns="http://www.w3.org/2000/svg">
+<svg width="2204px" height="146px" xmlns="http://www.w3.org/2000/svg">


Any idea why the width increased so much here?

View changes since the review

That is the git fetch command's full length before redacting content. This happens in other SVG tests.

### What does this PR try to resolve? It was added for libgit2 but not git-cli ### How to test and review this PR? I tested this by forcing git-cli for the relevant tests and they still passed. I did not add any tests for this because we will get coverage with rust-lang#17329. I avoided duplicating the tests for each git backend out of concern for getting more rate limits from github in CI.

rustbot · 2026-09-03T21:04:53Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

This changes the default for how we fetch to use the git CLI if present for better conformity and performance without breaking people (yet) who don't have it. Part of rust-lang#17227

rustbot assigned weihanglo Aug 6, 2026

rustbot added A-git Area: anything dealing with git S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 6, 2026

epage force-pushed the lazy-git branch from 5a6551a to df50afd Compare August 7, 2026 00:33

weihanglo reviewed Aug 16, 2026

View reviewed changes

weihanglo mentioned this pull request Aug 16, 2026

fix(git): git gc with safe.bareRepository=explicit #17370

Merged

epage mentioned this pull request Aug 27, 2026

fix(git): Remove ref status update when showing progress #17400

Merged

test(git): Call out that corrupt_git only works with libgit2

f0ecafc

epage force-pushed the lazy-git branch from df50afd to 6da26ff Compare August 28, 2026 21:35

This comment has been minimized.

Sign in to view

epage marked this pull request as draft August 28, 2026 21:35

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 28, 2026

test(git): Ensure libgit2 tests stay with libgit2

73513c4

If we get rid of ligit2 fetch, we'll need to re-evaluate how we do retry testing.

epage force-pushed the lazy-git branch from 6da26ff to 0032614 Compare September 3, 2026 16:42

epage marked this pull request as ready for review September 3, 2026 16:42

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 3, 2026

weihanglo added the T-cargo Team: Cargo label Sep 3, 2026

epage mentioned this pull request Sep 3, 2026

fix(git): Apply pr hint to git-fetch-with-cli #17437

Merged

rust-rfcbot added proposed-final-comment-period An FCP proposal has started, but not yet signed off. disposition-merge FCP with intent to merge labels Sep 3, 2026

weihanglo mentioned this pull request Sep 3, 2026

Migrate to CLI git fetching #17227

Open

weihanglo reviewed Sep 3, 2026

View reviewed changes

arlosi reviewed Sep 3, 2026

View reviewed changes

epage force-pushed the lazy-git branch from 0032614 to 3061a27 Compare September 3, 2026 21:04

epage force-pushed the lazy-git branch from 3061a27 to a2c5cc9 Compare September 3, 2026 21:06

rustbot added the A-documenting-cargo-itself Area: Cargo's documentation label Sep 3, 2026

epage force-pushed the lazy-git branch 3 times, most recently from 1aae7d6 to fd77c15 Compare September 4, 2026 15:48

weihanglo mentioned this pull request Sep 4, 2026

Tracking Issue for cargo config #9301

Open

14 tasks

epage added 2 commits September 4, 2026 11:52

test(git): Be more specific in http header prefixes

8c47116

fix(git)!: Default to net.git-fetch-with-cli if git is present

bfc1332

This changes the default for how we fetch to use the git CLI if present for better conformity and performance without breaking people (yet) who don't have it. Part of rust-lang#17227

epage force-pushed the lazy-git branch 5 times, most recently from 759b6f1 to bfc1332 Compare September 4, 2026 21:44

		@@ -1,7 +1,7 @@
		<svg width="740px" height="92px" xmlns="http://www.w3.org/2000/svg">
		<svg width="2204px" height="146px" xmlns="http://www.w3.org/2000/svg">

Uh oh!

Uh oh!

Conversation

epage commented Aug 6, 2026

What does this PR try to resolve?

How to test and review this PR?

Uh oh!

rustbot commented Aug 6, 2026

Uh oh!

weihanglo commented Aug 13, 2026

Uh oh!

weihanglo Aug 16, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

This comment has been minimized.

weihanglo commented Sep 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Benefits

Downsides

Uh oh!

rust-rfcbot commented Sep 3, 2026 • edited by Eh2406 Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

weihanglo Sep 3, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

arlosi Sep 3, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

rustbot commented Sep 3, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

weihanglo Aug 16, 2026 •

edited by rustbot

Loading

weihanglo commented Sep 3, 2026 •

edited

Loading

rust-rfcbot commented Sep 3, 2026 •

edited by Eh2406

Loading

weihanglo Sep 3, 2026 •

edited by rustbot

Loading

arlosi Sep 3, 2026 •

edited by rustbot

Loading