support minimal 'fetch' using gitoxide

This most notably excludes:

* progress
* SSH name guessing
* retry on spurious timeout/connection issues

Author: Byron

Cargo.toml

@@ -29,6 +29,7 @@ filetime = "0.2.9"
 flate2 = { version = "1.0.3", default-features = false, features = ["zlib"] }
 git2 = "0.15.0"
 git2-curl = "0.16.0"
+git-repository = { version = "0.29.0", features = ["blocking-http-transport-curl"] }
 glob = "0.3.0"
 hex = "0.4"
 home = "0.5"

src/cargo/sources/git/mod.rs

@@ -1,4 +1,5 @@
 pub use self::source::GitSource;
 pub use self::utils::{fetch, GitCheckout, GitDatabase, GitRemote};
+mod oxide;
 mod source;
 mod utils;

src/cargo/sources/git/oxide.rs

@@ -0,0 +1,69 @@
+//! This module contains all code sporting `gitoxide` for operations on `git` repositories and it mirrors
+//! `utils` closely for now. One day it can be renamed into `utils` once `git2` isn't required anymore.
+
+use crate::util::{network, Progress};
+use crate::{CargoResult, Config};
+use git_repository as git;
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
+use std::time::Duration;
+
+/// For the time being, `repo_path` makes it easy to instantiate a gitoxide repo just for fetching.
+/// In future this may change to be the gitoxide repository itself.
+pub fn with_retry_and_progress(
+    repo_path: &std::path::Path,
+    config: &Config,
+    cb: &mut (dyn FnMut(
+        &git::Repository,
+        &AtomicBool,
+        &mut git::progress::tree::Item,
+    ) -> CargoResult<()>
+              + Send),
+) -> CargoResult<()> {
+    let repo = git::open_opts(repo_path, {
+        let mut opts = git::open::Options::default();
+        // We need `git_binary` configuration as well for being able to see credential helpers
+        // that are configured with the `git` installation itself.
+        // However, this is slow on windows (~150ms) and most people won't need it as they use the
+        // standard index which won't ever need authentication.
+        // TODO: This is certainly something to make configurable, at the very least on windows.
+        //       Maybe it's also something that could be cached, all we need is the path to the configuration file
+        //       which usually doesn't change unless the installation changes. Maybe something keyed by the location of the
+        //       binary along with its fingerprint.
+        opts.permissions.config = git::permissions::Config::all();
+        opts
+    })?;
+
+    let progress_root: Arc<git::progress::tree::Root> = git::progress::tree::root::Options {
+        initial_capacity: 10,
+        message_buffer_capacity: 10,
+    }
+    .into();
+    let mut progress = progress_root.add_child("operation");
+
+    // For decent interrupts of long-running computations and removal of temp files we should handle interrupts, and this
+    // is an easy way to do that. We will remove them later.
+    // We intentionally swallow errors here as if for some reason we can't register handlers, `cargo` will just work like before and
+    // abort on signals.
+    let _deregister_signal_handlers_on_drop = git::interrupt::init_handler(|| {})
+        .ok()
+        .unwrap_or_default()
+        .auto_deregister();
+    let should_interrupt = AtomicBool::new(false);
+    let _progress_bar = Progress::new("Fetch", config);
+    std::thread::scope(move |s| {
+        s.spawn({
+            let root = Arc::downgrade(&progress_root);
+            move || -> CargoResult<()> {
+                let mut tasks = Vec::with_capacity(10);
+                while let Some(root) = root.upgrade() {
+                    root.sorted_snapshot(&mut tasks);
+                    // dbg!(&tasks);
+                    std::thread::sleep(Duration::from_millis(300));
+                }
+                Ok(())
+            }
+        });
+        network::with_retry(config, || cb(&repo, &should_interrupt, &mut progress))
+    })
+}

src/cargo/sources/git/utils.rs

@@ -2,6 +2,7 @@
 //! authentication/cloning.
 
 use crate::core::GitReference;
+use crate::sources::git::oxide;
 use crate::util::errors::CargoResult;
 use crate::util::{human_readable_bytes, network, Config, IntoUrl, MetricsCounter, Progress};
 use anyhow::{anyhow, Context as _};
@@ -855,51 +856,123 @@ pub fn fetch(
     if let Some(true) = config.net_config()?.git_fetch_with_cli {
         return fetch_with_cli(repo, url, &refspecs, tags, config);
     }
-
-    debug!("doing a fetch for {}", url);
-    let git_config = git2::Config::open_default()?;
-    with_fetch_options(&git_config, url, config, &mut |mut opts| {
-        if tags {
-            opts.download_tags(git2::AutotagOption::All);
-        }
-        // The `fetch` operation here may fail spuriously due to a corrupt
-        // repository. It could also fail, however, for a whole slew of other
-        // reasons (aka network related reasons). We want Cargo to automatically
-        // recover from corrupt repositories, but we don't want Cargo to stomp
-        // over other legitimate errors.
-        //
-        // Consequently we save off the error of the `fetch` operation and if it
-        // looks like a "corrupt repo" error then we blow away the repo and try
-        // again. If it looks like any other kind of error, or if we've already
-        // blown away the repository, then we want to return the error as-is.
-        let mut repo_reinitialized = false;
-        loop {
-            debug!("initiating fetch of {:?} from {}", refspecs, url);
-            let res = repo
-                .remote_anonymous(url)?
-                .fetch(&refspecs, Some(&mut opts), None);
-            let err = match res {
-                Ok(()) => break,
-                Err(e) => e,
-            };
-            debug!("fetch failed: {}", err);
-
-            if !repo_reinitialized && matches!(err.class(), ErrorClass::Reference | ErrorClass::Odb)
-            {
-                repo_reinitialized = true;
-                debug!(
-                    "looks like this is a corrupt repository, reinitializing \
+    if config
+        .cli_unstable()
+        .gitoxide
+        .map_or(false, |git| git.fetch)
+    {
+        use git::remote::fetch::Error;
+        use git_repository as git;
+        let git2_repo = repo;
+        oxide::with_retry_and_progress(
+            &git2_repo.path().to_owned(),
+            config,
+            &mut |repo, should_interrupt, progress| {
+                // The `fetch` operation here may fail spuriously due to a corrupt
+                // repository. It could also fail, however, for a whole slew of other
+                // reasons (aka network related reasons). We want Cargo to automatically
+                // recover from corrupt repositories, but we don't want Cargo to stomp
+                // over other legitimate errors.
+                //
+                // Consequently we save off the error of the `fetch` operation and if it
+                // looks like a "corrupt repo" error then we blow away the repo and try
+                // again. If it looks like any other kind of error, or if we've already
+                // blown away the repository, then we want to return the error as-is.
+                let mut repo_reinitialized = false;
+                let mut repo_storage;
+                let mut repo = &*repo;
+                loop {
+                    debug!("initiating fetch of {:?} from {}", refspecs, url);
+                    let res = repo
+                        .remote_at(url)?
+                        .with_refspecs(
+                            refspecs.iter().map(|s| s.as_str()),
+                            git::remote::Direction::Fetch,
+                        )?
+                        .connect(git::remote::Direction::Fetch, progress.add_child("fetch"))?
+                        .prepare_fetch(git::remote::ref_map::Options::default())?
+                        .receive(should_interrupt);
+                    let err = match res {
+                        Ok(_) => break,
+                        Err(e) => e,
+                    };
+                    debug!("fetch failed: {}", err);
+
+                    if !repo_reinitialized
+                        && matches!(
+                            err,
+                            Error::Configuration { .. }
+                                | Error::IncompatibleObjectHash { .. }
+                                | Error::WritePack(_)
+                                | Error::UpdateRefs(_)
+                                | Error::RemovePackKeepFile { .. }
+                        )
+                    {
+                        repo_reinitialized = true;
+                        debug!(
+                            "looks like this is a corrupt repository, reinitializing \
                      and trying again"
-                );
-                if reinitialize(repo).is_ok() {
-                    continue;
+                        );
+                        if reinitialize(git2_repo).is_ok() {
+                            repo_storage =
+                                git::open_opts(repo.path(), repo.open_options().to_owned())?;
+                            repo = &repo_storage;
+                            continue;
+                        }
+                    }
+
+                    return Err(err.into());
                 }
+                Ok(())
+            },
+        )
+    } else {
+        debug!("doing a fetch for {}", url);
+        let git_config = git2::Config::open_default()?;
+        with_fetch_options(&git_config, url, config, &mut |mut opts| {
+            if tags {
+                opts.download_tags(git2::AutotagOption::All);
             }
+            // The `fetch` operation here may fail spuriously due to a corrupt
+            // repository. It could also fail, however, for a whole slew of other
+            // reasons (aka network related reasons). We want Cargo to automatically
+            // recover from corrupt repositories, but we don't want Cargo to stomp
+            // over other legitimate errors.
+            //
+            // Consequently we save off the error of the `fetch` operation and if it
+            // looks like a "corrupt repo" error then we blow away the repo and try
+            // again. If it looks like any other kind of error, or if we've already
+            // blown away the repository, then we want to return the error as-is.
+            let mut repo_reinitialized = false;
+            loop {
+                debug!("initiating fetch of {:?} from {}", refspecs, url);
+                let res = repo
+                    .remote_anonymous(url)?
+                    .fetch(&refspecs, Some(&mut opts), None);
+                let err = match res {
+                    Ok(()) => break,
+                    Err(e) => e,
+                };
+                debug!("fetch failed: {}", err);
+
+                if !repo_reinitialized
+                    && matches!(err.class(), ErrorClass::Reference | ErrorClass::Odb)
+                {
+                    repo_reinitialized = true;
+                    debug!(
+                        "looks like this is a corrupt repository, reinitializing \
+                     and trying again"
+                    );
+                    if reinitialize(repo).is_ok() {
+                        continue;
+                    }
+                }
 
-            return Err(err.into());
-        }
-        Ok(())
-    })
+                return Err(err.into());
+            }
+            Ok(())
+        })
+    }
 }
 
 fn fetch_with_cli(