feat: add file::Store::is_empty()

Author: Byron

gix-ref/src/store/file/mod.rs

@@ -53,7 +53,7 @@ mod access {
         }
     }
 
-    use crate::file;
+    use crate::{file, Target};
 
     /// Access
     impl file::Store {
@@ -78,6 +78,35 @@ mod access {
         pub fn common_dir_resolved(&self) -> &Path {
             self.common_dir.as_deref().unwrap_or(&self.git_dir)
         }
+
+        /// Return `Some(true)` if this is a freshly initialized ref store without any observable changes.
+        /// Return `None` if `HEAD` couldn't be read.
+        ///
+        /// This is the case if:
+        ///
+        /// * the ref-store is valid
+        /// * `HEAD` exists
+        /// * `HEAD` still points to `default_ref`
+        /// * there are no packed refs
+        /// * There are no observable references in `refs/`
+        pub fn is_pristine(&self, default_ref: &crate::FullNameRef) -> Option<bool> {
+            let head = self.find_loose("HEAD").ok()?;
+            match head.target {
+                Target::Object(_) => return Some(false),
+                Target::Symbolic(name) => {
+                    if name.as_ref() != default_ref {
+                        return Some(false);
+                    }
+                }
+            }
+            if self.loose_iter().ok()?.filter_map(Result::ok).next().is_some() {
+                return Some(false);
+            }
+            if self.packed_refs_path().is_file() {
+                return Some(false);
+            }
+            Some(true)
+        }
     }
 }
 

gix-ref/tests/fixtures/generated-archives/make_pristine.tar

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -eu -o pipefail
+
+git init untouched
+
+git init changed-headref
+(cd changed-headref
+  echo "ref: refs/heads/other" >.git/HEAD
+)
+
+git init detached
+(cd detached
+  echo "abcdefabcdefabcdefabcdefabcdefabcdefabcd" >.git/HEAD
+)
+
+git init invalid-loose-ref
+(cd invalid-loose-ref
+  touch .git/refs/heads/empty
+)

gix-ref/tests/fixtures/make_pristine.sh

@@ -14,8 +14,12 @@ pub fn store_with_packed_refs() -> crate::Result<Store> {
 }
 
 pub fn store_at(name: &str) -> crate::Result<Store> {
-    let path = gix_testtools::scripted_fixture_read_only_standalone(name)?;
-    Ok(Store::at(path.join(".git"), Default::default()))
+    named_store_at(name, "")
+}
+
+pub fn named_store_at(script_name: &str, name: &str) -> crate::Result<Store> {
+    let path = gix_testtools::scripted_fixture_read_only_standalone(script_name)?;
+    Ok(Store::at(path.join(name).join(".git"), Default::default()))
 }
 
 pub fn store_at_with_args(name: &str, args: impl IntoIterator<Item = impl Into<String>>) -> crate::Result<Store> {

gix-ref/tests/refs/file/mod.rs

@@ -1,4 +1,4 @@
-use crate::file::store;
+use crate::file::{named_store_at, store};
 
 #[test]
 fn set_packed_buffer_mmap_threshold() -> crate::Result {
@@ -20,3 +20,22 @@ fn set_packed_buffer_mmap_threshold() -> crate::Result {
     );
     Ok(())
 }
+
+#[test]
+fn is_pristine() -> crate::Result {
+    let store = named_store_at("make_pristine.sh", "untouched")?;
+    assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(true));
+    assert_eq!(store.is_pristine("refs/heads/other".try_into()?), Some(false));
+
+    let store = named_store_at("make_pristine.sh", "changed-headref")?;
+    assert_eq!(store.is_pristine("refs/heads/other".try_into()?), Some(true));
+    assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
+
+    let store = named_store_at("make_pristine.sh", "detached")?;
+    assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
+
+    let store = named_store_at("make_pristine.sh", "invalid-loose-ref")?;
+    assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(true));
+
+    Ok(())
+}

gix-ref/tests/refs/file/store/access.rs

@@ -9,6 +9,7 @@ mod existing {
             "make_packed_ref_repository_for_overlay.sh",
         ] {
             let store = store_at(fixture)?;
+            assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
             let c1 = hex_to_id("134385f6d781b7e97062102c6a483440bfda2a03");
             let r = store.find("main")?;
             assert_eq!(r.target.into_id(), c1);

gix-ref/tests/refs/file/store/find.rs

@@ -576,6 +576,7 @@ fn overlay_partial_prefix_iter_when_prefix_is_dir() -> crate::Result {
     use gix_ref::Target::*;
 
     let store = store_at("make_packed_ref_repository_for_overlay.sh")?;
+    assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
     let c1 = hex_to_id("134385f6d781b7e97062102c6a483440bfda2a03");
 
     let ref_names = store

gix-ref/tests/refs/file/store/iter.rs

@@ -84,6 +84,7 @@ mod read_only {
     fn linked() -> crate::Result {
         for packed in [false, true] {
             let (store, odb, _tmp) = worktree_store(packed, "w1", Mode::Read)?;
+            assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
             let peel = into_peel(&store, odb);
 
             let w1_head_id = peel(store.find("HEAD").unwrap());
@@ -132,6 +133,7 @@ mod read_only {
     fn main() -> crate::Result {
         for packed in [false, true] {
             let (store, odb, _tmp) = main_store(packed, Mode::Read)?;
+            assert_eq!(store.is_pristine("refs/heads/main".try_into()?), Some(false));
             let peel = into_peel(&store, odb);
 
             let head_id = peel(store.find("HEAD").unwrap());