feat: add Repository::is_empty() to emulate the similar git2 API

Author: Byron

gix/src/repository/location.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::path::{Path, PathBuf};
 
 use gix_path::realpath::MAX_SYMLINKS;
@@ -108,4 +109,19 @@ impl crate::Repository {
             None => crate::repository::Kind::Bare,
         }
     }
+
+    /// Returns `Some(true)` if the reference database [is untouched](gix_ref::file::Store::is_pristine()).
+    /// This typically indicates that the repository is new and empty.
+    /// Return `None` if a defect in the database makes the answer uncertain.
+    pub fn is_pristine(&self) -> Option<bool> {
+        let name = self
+            .config
+            .resolved
+            .string(crate::config::tree::Init::DEFAULT_BRANCH)
+            .unwrap_or(Cow::Borrowed("master".into()));
+        let default_branch_ref_name: gix_ref::FullName = format!("refs/heads/{name}")
+            .try_into()
+            .unwrap_or_else(|_| gix_ref::FullName::try_from("refs/heads/master").expect("known to be valid"));
+        self.refs.is_pristine(default_branch_ref_name.as_ref())
+    }
 }

gix/tests/gix/repository/mod.rs

@@ -56,6 +56,16 @@ mod index {
             repo.index_or_load_from_head_or_empty()?.entries().is_empty(),
             "an empty index is created on the fly"
         );
+        assert_eq!(
+            repo.is_pristine(),
+            Some(false),
+            "not pristine as it things the initial ref was changed to 'main'"
+        );
+        assert_eq!(
+            repo.refs.is_pristine("refs/heads/main".try_into()?),
+            Some(true),
+            "This is a quirk of default values in gix and the way we override the initial branch for test fixtures"
+        );
         Ok(())
     }
 }