Bug 16194

Scenario I am describing is that multiple recipes fetch the same repo, but one of them is not requesting git-lfs data (lfs=0) and another one does (lfs=1).

If we have BB_GIT_SHALLOW enabled for those recipes, there is a risk that if do_fetch for recipe *not* requesting git-lfs data (let's call it foo.bb) runs before the other one - bar.bb, do_unpack for bar.bb will fail as it won't be able to retrieve git-lfs data from remote.

Here is a "synthetic test" for that scenario:
```
diff --git a/lib/bb/tests/fetch.py b/lib/bb/tests/fetch.py
index 74eb73472..028639ba1 100644
--- a/lib/bb/tests/fetch.py
+++ b/lib/bb/tests/fetch.py
@@ -2600,6 +2600,28 @@ class GitLfsTest(FetcherTest):
             shutil.rmtree(self.gitdir, ignore_errors=True)
             fetcher.unpack(self.d.getVar('WORKDIR'))
 
+    @skipIfNoGitLFS()
+    @skipIfNoNetwork()
+    def test_shallow_tarball_with_lfs(self):
+        uri = "git://gitlab.com/gitlab-examples/lfs.git;protocol=https;branch=master"
+
+        # Use shallow tarballs
+        self.d.setVar('BB_GIT_SHALLOW', '1')
+        self.d.setVar('BB_GENERATE_SHALLOW_TARBALLS', '1')
+
+        # Download without git-lfs
+        self.d.setVar('SRC_URI', uri + ";lfs=0")
+        fetcher, ud = self.fetch()
+
+        # Redownload with git-lfs
+        self.d.setVar('SRC_URI', uri + ";lfs=1")
+        fetcher, ud = self.fetch()
+
+        # Attempt unpack without network
+        bb.utils.disable_network()
+        fetcher.unpack(self.d.getVar('WORKDIR'))
+
+
 class GitURLWithSpacesTest(FetcherTest):
     test_git_urls = {
         "git://tfs-example.org:22/tfs/example%20path/example.git;branch=master" : {
```

You should run above test with `bin/bitbake-selftest bb.tests.fetch.GitLfsTest -k test_shallow_tarball_with_lfs`.

*Expected behavior*: Test passes, because when bitbake is supposed to download a shallow tarball with git-lfs blobs, it will check whether the git-lfs blobs are actually available and download them if needed.

*Actual behavior*: Test fails at the unpack step with git-lfs unable to fetch the blob.

I fear that to properly support such case without doing tarball content checks all the time, we would have to split the git-lfs blobs into a separate tarball. Then if a recipe sets lfs=1, both shallow tarball and lfs tarball would be unpacked. It could also be reused for full mirror tarballs, because from what I checked it can also affect them.

---

Side topic, I had to use `bb.utils.disable_network()` as I found no other way to disable network access for the unpack functionality in the tests. However it is not a viable way to actually do this as it affects the entire testing process and subsequent network tests will fail.