feat: add clone::PrepareFetch::with_in_memory_config_overrides().

With it one can affect the repository configuration right before fetching.

gix/src/clone/access.rs

@@ -10,7 +10,7 @@ impl PrepareFetch {
     /// _all changes done in `f()` will be persisted_.
     ///
     /// It can also be used to configure additional options, like those for fetching tags. Note that
-    /// [`with_fetch_tags()`][crate::Remote::with_fetch_tags()] should be called here to configure the clone as desired.
+    /// [`with_fetch_tags()`](crate::Remote::with_fetch_tags()) should be called here to configure the clone as desired.
     /// Otherwise a clone is configured to be complete and fetches all tags, not only those reachable from all branches.
     pub fn configure_remote(
         mut self,
@@ -21,7 +21,7 @@ impl PrepareFetch {
     }
 
     /// Set the remote's name to the given value after it was configured using the function provided via
-    /// [`configure_remote()`][Self::configure_remote()].
+    /// [`configure_remote()`](Self::configure_remote()).
     ///
     /// If not set here, it defaults to `origin` or the value of `clone.defaultRemoteName`.
     pub fn with_remote_name(mut self, name: impl Into<BString>) -> Result<Self, crate::remote::name::Error> {
@@ -35,10 +35,11 @@ impl PrepareFetch {
         self
     }
 
-    /// Apply the given configuration `values` early to allow affecting the repository instantiation phase.
-    /// The configuration is marked with [source API][gix_config::Source::Api].
-    pub fn config_overrides(mut self, values: impl IntoIterator<Item = impl Into<BString>>) -> Self {
-        self.api_config_overrides = values.into_iter().map(Into::into).collect();
+    /// Apply the given configuration `values` right before readying the actual fetch from the remote.
+    /// The configuration is marked with [source API](gix_config::Source::Api), and will not be written back, it's
+    /// retained only in memory.
+    pub fn with_in_memory_config_overrides(mut self, values: impl IntoIterator<Item = impl Into<BString>>) -> Self {
+        self.config_overrides = values.into_iter().map(Into::into).collect();
         self
     }
 }

gix/src/clone/fetch/mod.rs

@@ -79,9 +79,11 @@ impl PrepareFetch {
             .as_mut()
             .expect("user error: multiple calls are allowed only until it succeeds");
 
-        let mut snapshot = repo.config_snapshot_mut();
-        snapshot.append_config(self.api_config_overrides.as_slice(), gix_config::Source::Api)?;
-        snapshot.commit()?;
+        if !self.config_overrides.is_empty() {
+            let mut snapshot = repo.config_snapshot_mut();
+            snapshot.append_config(&self.config_overrides, gix_config::Source::Api)?;
+            snapshot.commit()?;
+        }
 
         let remote_name = match self.remote_name.as_ref() {
             Some(name) => name.to_owned(),

gix/src/clone/mod.rs

@@ -21,7 +21,7 @@ pub struct PrepareFetch {
     /// The name of the remote, which defaults to `origin` if not overridden.
     remote_name: Option<BString>,
     /// Additional config `values` that are applied in-memory before starting the fetch process.
-    api_config_overrides: Vec<BString>,
+    config_overrides: Vec<BString>,
     /// A function to configure a remote prior to fetching a pack.
     configure_remote: Option<ConfigureRemoteFn>,
     /// A function to configure a connection before using it.
@@ -128,7 +128,7 @@ impl PrepareFetch {
             #[cfg(any(feature = "async-network-client", feature = "blocking-network-client"))]
             fetch_options: Default::default(),
             repo: Some(repo),
-            api_config_overrides: Vec::new(),
+            config_overrides: Vec::new(),
             remote_name: None,
             configure_remote: None,
             #[cfg(any(feature = "async-network-client", feature = "blocking-network-client"))]
@@ -147,8 +147,6 @@ pub struct PrepareCheckout {
     pub(self) repo: Option<crate::Repository>,
 }
 
-mod access;
-
 // This module encapsulates functionality that works with both feature toggles. Can be combined with `fetch`
 // once async and clone are a thing.
 #[cfg(any(feature = "async-network-client", feature = "blocking-network-client"))]
@@ -184,6 +182,8 @@ mod access_feat {
 #[cfg(any(feature = "async-network-client-async-std", feature = "blocking-network-client"))]
 pub mod fetch;
 
+mod access;
+
 ///
 #[cfg(feature = "worktree-mutation")]
 pub mod checkout;

gix/tests/clone/mod.rs

@@ -109,6 +109,7 @@ mod blocking_io {
     fn from_shallow_allowed_by_default() -> crate::Result {
         let tmp = gix_testtools::tempfile::TempDir::new()?;
         let (repo, _change) = gix::prepare_clone_bare(remote::repo("base.shallow").path(), tmp.path())?
+            .with_in_memory_config_overrides(Some("my.marker=1"))
             .fetch_only(gix::progress::Discard, &std::sync::atomic::AtomicBool::default())?;
         assert_eq!(
             repo.shallow_commits()?.expect("present").as_slice(),
@@ -118,6 +119,18 @@ mod blocking_io {
                 hex_to_id("dfd0954dabef3b64f458321ef15571cc1a46d552"),
             ]
         );
+        assert_eq!(
+            repo.config_snapshot().boolean("my.marker"),
+            Some(true),
+            "configuration overrides are set in time"
+        );
+        assert_eq!(
+            gix::open_opts(repo.git_dir(), gix::open::Options::isolated())?
+                .config_snapshot()
+                .boolean("my.marker"),
+            None,
+            "these options are not persisted"
+        );
         Ok(())
     }