fix: rev-spec parsing can now handle the empty tree as full hex hash. (#470)

Even though the empty-tree object can be found when searched via
`Repository::find_object()`, previously it was not locatable when
used during rev-spec parsing.

Author: Byron

git-repository/src/revision/spec/parse/delegate/revision.rs

@@ -40,7 +40,16 @@ impl<'repo> delegate::Revision for Delegate<'repo> {
         self.last_call_was_disambiguate_prefix[self.idx] = true;
         let mut candidates = Some(HashSet::default());
         self.prefix[self.idx] = Some(prefix);
-        match self.repo.objects.lookup_prefix(prefix, candidates.as_mut()) {
+
+        let empty_tree_id = git_hash::ObjectId::empty_tree(prefix.as_oid().kind());
+        let res = if prefix.as_oid() == empty_tree_id {
+            candidates.as_mut().expect("set").insert(empty_tree_id);
+            Ok(Some(Err(())))
+        } else {
+            self.repo.objects.lookup_prefix(prefix, candidates.as_mut())
+        };
+
+        match res {
             Err(err) => {
                 self.err.push(object::find::existing::Error::Find(err).into());
                 None

git-repository/tests/fixtures/generated-archives/make_diff_repo.tar.xz

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2123aa9e3fd85166d35c02c59ce8f0e8aaa3631c3dd4e43468f98d26cddf049c
+size 11128

git-repository/tests/fixtures/generated-archives/make_rev_spec_parse_repos.tar.xz

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:4de4199add061d1ef825b392162898fcf4da67f69c5d588012fe4d71465c768f
-size 28372
+oid sha256:0edf5366df74aaeb3c58ad070f9f9a522d0fae049f0905b7372ff28d0b3628bf
+size 28716

git-repository/tests/fixtures/make_diff_repo.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+set -eu -o pipefail
+
+git init -q
+
+git checkout -b main
+mkdir dir
+touch a b dir/c
+git add .
+git commit -q -m c1
+
+echo a >> a
+echo b >> b
+echo dir/c >> dir/c
+git commit -q -am c2
+
+echo a1 >> a
+git commit -q -am c3

git-repository/tests/fixtures/make_rev_spec_parse_repos.sh

@@ -389,6 +389,7 @@ git init complex_graph
 
   baseline "@^{tree}"
   baseline "@:"
+  baseline "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
 )
 
 git init new

git-repository/tests/object/tree.rs

@@ -1,5 +1,5 @@
 mod diff {
-    use crate::remote;
+    use crate::named_repo;
     use git_object::bstr::ByteSlice;
     use git_object::tree::EntryMode;
     use git_repository as git;
@@ -8,9 +8,9 @@ mod diff {
 
     #[test]
     fn changes_against_tree_modified() {
-        let repo = remote::repo("base");
-        let from = tree_named(&repo, "g");
-        let to = tree_named(&repo, "h");
+        let repo = named_repo("make_diff_repo.sh").unwrap();
+        let from = tree_named(&repo, "@^{/c3}~1");
+        let to = tree_named(&repo, ":/c3");
         from.changes()
             .for_each_to_obtain_tree(&to, |change| -> Result<_, Infallible> {
                 assert_eq!(change.location, "", "without configuration the location field is empty");
@@ -23,22 +23,33 @@ mod diff {
                     } => {
                         assert_eq!(previous_entry_mode, EntryMode::Blob);
                         assert_eq!(entry_mode, EntryMode::Blob);
-                        assert_eq!(previous_id.object().unwrap().data.as_bstr(), "g\n");
-                        assert_eq!(id.object().unwrap().data.as_bstr(), "h\n");
+                        assert_eq!(previous_id.object().unwrap().data.as_bstr(), "a\n");
+                        assert_eq!(id.object().unwrap().data.as_bstr(), "a\na1\n");
                         Ok(Default::default())
                     }
                     Event::Deletion { .. } | Event::Addition { .. } => unreachable!("only modification is expected"),
                 }
             })
             .unwrap();
+    }
+    #[test]
+    fn changes_against_tree_with_filename_tracking() {
+        let repo = named_repo("make_diff_repo.sh").unwrap();
+        let from = tree_named(
+            &repo,
+            &git::hash::ObjectId::empty_tree(git::hash::Kind::Sha1).to_string(),
+        );
+        let to = tree_named(&repo, ":/c1");
 
+        let mut expected = vec!["a", "b", "c"];
         from.changes()
             .track_filename()
             .for_each_to_obtain_tree(&to, |change| -> Result<_, Infallible> {
-                assert_eq!(change.location, "file");
-                Ok(git::object::tree::diff::Action::Continue)
+                expected.retain(|name| name != change.location);
+                Ok(Default::default())
             })
             .unwrap();
+        assert_eq!(expected, Vec::<&str>::new(), "all paths should have been seen")
     }
 
     fn tree_named<'repo>(repo: &'repo git::Repository, rev_spec: &str) -> git::Tree<'repo> {

git-repository/tests/revision/spec/from_bytes/mod.rs

@@ -123,3 +123,12 @@ fn access_blob_through_tree() {
         "Could not find path \"missing\" in tree 0000000000c of parent object 0000000000c"
     );
 }
+
+#[test]
+fn empty_tree_as_full_name() {
+    let repo = repo("complex_graph").unwrap();
+    assert_eq!(
+        parse_spec("4b825dc642cb6eb9a060e54bf8d69288fbee4904", &repo).unwrap(),
+        Spec::from_id(hex_to_id("4b825dc642cb6eb9a060e54bf8d69288fbee4904").attach(&repo))
+    );
+}