Allow fetching a single object, shallow or not.

Doing so seems cleaner as there should be no logical difference between
shallow or not-shallow when fetching. We want a specific object, and should
get it with the refspec. `git` will assure we see all objects we need,
handling shallow-ness for us.

Note that one test needed adjustments due to the different mechanism used
when fetching local repositories, requiring more changes to properly 'break'
the submodule repo when `gitoxide` is used.

Author: Byron

src/cargo/sources/git/utils.rs

@@ -855,7 +855,6 @@ pub fn fetch(
 
     // If we're fetching from GitHub, attempt GitHub's special fast path for
     // testing if we've already got an up-to-date copy of the repository.
-    let is_shallow = !matches!(shallow, gix::remote::fetch::Shallow::NoChange);
     let oid_to_fetch = match github_fast_path(repo, orig_url, reference, config) {
         Ok(FastPathRev::UpToDate) => return Ok(()),
         Ok(FastPathRev::NeedsFetch(rev)) => Some(rev),
@@ -901,10 +900,10 @@ pub fn fetch(
                 refspecs.push(format!("+{0}:{0}", rev));
             } else if let Some(oid_to_fetch) = oid_to_fetch {
                 refspecs.push(format!("+{0}:refs/commit/{0}", oid_to_fetch));
-            } else if is_shallow && rev.parse::<Oid>().is_ok() {
+            } else if rev.parse::<Oid>().is_ok() {
                 // There is a specific commit to fetch and we will just do so in shallow-mode only
                 // to not disturb the previous logic. Note that with typical settings for shallowing,
-                // With shallow histories this is a bit fuzzy, and we opt-out for now.
+                // we will just fetch a single `rev` as single commit.
                 refspecs.push(format!("+{0}:refs/remotes/origin/HEAD", rev));
             } else {
                 // We don't know what the rev will point to. To handle this

tests/testsuite/git.rs

@@ -948,6 +948,13 @@ fn dep_with_bad_submodule() {
             None,
         )
         .unwrap();
+    std::fs::remove_file(
+        repo.path()
+            .join("objects")
+            .join(&commit.id().to_string()[..2])
+            .join(&commit.id().to_string()[2..]),
+    )
+    .unwrap();
 
     let p = project
         .file(
@@ -972,9 +979,36 @@ fn dep_with_bad_submodule() {
             "extern crate dep1; pub fn foo() { dep1::dep() }",
         )
         .build();
+    let expected = if cargo_uses_gitoxide() {
+        format!(
+            "\
+[UPDATING] git repository [..]
+[UPDATING] git submodule `file://[..]/dep2`
+[ERROR] failed to get `dep1` as a dependency of package `foo v0.5.0 [..]`
+
+Caused by:
+  failed to load source for dependency `dep1`
+
+Caused by:
+  Unable to update {}
+
+Caused by:
+  failed to update submodule `src`
 
-    let expected = format!(
-        "\
+Caused by:
+  failed to fetch submodule `src` from [..]
+
+Caused by:
+  Could not decode server reply
+
+Caused by:
+  upload-pack: not our ref [..]
+",
+            path2url(git_project.root())
+        )
+    } else {
+        format!(
+            "\
 [UPDATING] git repository [..]
 [UPDATING] git submodule `file://[..]/dep2`
 [ERROR] failed to get `dep1` as a dependency of package `foo v0.5.0 [..]`
@@ -989,10 +1023,14 @@ Caused by:
   failed to update submodule `src`
 
 Caused by:
-  object not found - no match for id [..]
+  failed to fetch submodule `src` from [..]
+
+Caused by:
+  target OID for the reference doesn't exist on the repository; class=Reference (4)
 ",
-        path2url(git_project.root())
-    );
+            path2url(git_project.root())
+        )
+    };
 
     p.cargo("check")
         .with_stderr(expected)