2 files changed, 90 insertions, 6 deletions

diff --git a/bitbake/lib/bb/fetch2/git.py b/bitbake/lib/bb/fetch2/git.py
index 4d6e57ade7..9ecc855af8 100644
--- a/bitbake/lib/bb/fetch2/git.py
+++ b/bitbake/lib/bb/fetch2/git.py
@@ -307,7 +307,10 @@ class Git(FetchMethod):
         return ud.clonedir
 
     def need_update(self, ud, d):
-        return self.clonedir_need_update(ud, d) or self.shallow_tarball_need_update(ud) or self.tarball_need_update(ud)
+        return self.clonedir_need_update(ud, d) \
+                or self.shallow_tarball_need_update(ud) \
+                or self.tarball_need_update(ud) \
+                or self.lfs_need_update(ud, d)
 
     def clonedir_need_update(self, ud, d):
         if not os.path.exists(ud.clonedir):
@@ -319,6 +322,15 @@ class Git(FetchMethod):
                 return True
         return False
 
+    def lfs_need_update(self, ud, d):
+        if self.clonedir_need_update(ud, d):
+            return True
+
+        for name in ud.names:
+            if not self._lfs_objects_downloaded(ud, d, name, ud.clonedir):
+                return True
+        return False
+
     def clonedir_need_shallow_revs(self, ud, d):
         for rev in ud.shallow_revs:
             try:
@@ -406,7 +418,7 @@ class Git(FetchMethod):
             if missing_rev:
                 raise bb.fetch2.FetchError("Unable to find revision %s even from upstream" % missing_rev)
 
-        if self._contains_lfs(ud, d, ud.clonedir) and self._need_lfs(ud):
+        if self.lfs_need_update(ud, d):
             # Unpack temporary working copy, use it to run 'git checkout' to force pre-fetching
             # of all LFS blobs needed at the srcrev.
             #
@@ -649,6 +661,35 @@ class Git(FetchMethod):
             raise bb.fetch2.FetchError("The command '%s' gave output with more then 1 line unexpectedly, output: '%s'" % (cmd, output))
         return output.split()[0] != "0"
 
+    def _lfs_objects_downloaded(self, ud, d, name, wd):
+        """
+        Verifies whether the LFS objects for requested revisions have already been downloaded
+        """
+        # Bail out early if this repository doesn't use LFS
+        if not self._need_lfs(ud) or not self._contains_lfs(ud, d, wd):
+            return True
+
+        # The Git LFS specification specifies ([1]) the LFS folder layout so it should be safe to check for file
+        # existence.
+        # [1] https://github.com/git-lfs/git-lfs/blob/main/docs/spec.md#intercepting-git
+        cmd = "%s lfs ls-files -l %s" \
+                % (ud.basecmd, ud.revisions[name])
+        output = runfetchcmd(cmd, d, quiet=True, workdir=wd).rstrip()
+        # Do not do any further matching if no objects are managed by LFS
+        if not output:
+            return True
+
+        # Match all lines beginning with the hexadecimal OID
+        oid_regex = re.compile("^(([a-fA-F0-9]{2})([a-fA-F0-9]{2})[A-Fa-f0-9]+)")
+        for line in output.split("\n"):
+            oid = re.search(oid_regex, line)
+            if not oid:
+                bb.warn("git lfs ls-files output '%s' did not match expected format." % line)
+            if not os.path.exists(os.path.join(wd, "lfs", "objects", oid.group(2), oid.group(3), oid.group(1))):
+                return False
+
+        return True
+
     def _need_lfs(self, ud):
         return ud.parm.get("lfs", "1") == "1"
 
diff --git a/bitbake/lib/bb/tests/fetch.py b/bitbake/lib/bb/tests/fetch.py
index 847a35602d..5aa3e464dd 100644
--- a/bitbake/lib/bb/tests/fetch.py
+++ b/bitbake/lib/bb/tests/fetch.py
@@ -6,6 +6,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 #
 
+import contextlib
 import unittest
 import hashlib
 import tempfile
@@ -2182,10 +2183,14 @@ class GitLfsTest(FetcherTest):
 
         bb.utils.mkdirhier(self.srcdir)
         self.git_init(cwd=self.srcdir)
-        with open(os.path.join(self.srcdir, '.gitattributes'), 'wt') as attrs:
-            attrs.write('*.mp3 filter=lfs -text')
-        self.git(['add', '.gitattributes'], cwd=self.srcdir)
-        self.git(['commit', '-m', "attributes", '.gitattributes'], cwd=self.srcdir)
+        self.commit_file('.gitattributes', '*.mp3 filter=lfs -text')
+
+    def commit_file(self, filename, content):
+        with open(os.path.join(self.srcdir, filename), "w") as f:
+            f.write(content)
+        self.git(["add", filename], cwd=self.srcdir)
+        self.git(["commit", "-m", "Change"], cwd=self.srcdir)
+        return self.git(["rev-parse", "HEAD"], cwd=self.srcdir).strip()
 
     def fetch(self, uri=None, download=True):
         uris = self.d.getVar('SRC_URI').split()
@@ -2206,6 +2211,44 @@ class GitLfsTest(FetcherTest):
         return unpacked_lfs_file
 
     @skipIfNoGitLFS()
+    def test_fetch_lfs_on_srcrev_change(self):
+        """Test if fetch downloads missing LFS objects when a different revision within an existing repository is requested"""
+        self.git(["lfs", "install", "--local"], cwd=self.srcdir)
+
+        @contextlib.contextmanager
+        def hide_upstream_repository():
+            """Hide the upstream repository to make sure that git lfs cannot pull from it"""
+            temp_name = self.srcdir + ".bak"
+            os.rename(self.srcdir, temp_name)
+            try:
+                yield
+            finally:
+                os.rename(temp_name, self.srcdir)
+
+        def fetch_and_verify(revision, filename, content):
+            self.d.setVar('SRCREV', revision)
+            fetcher, ud = self.fetch()
+
+            with hide_upstream_repository():
+                workdir = self.d.getVar('WORKDIR')
+                fetcher.unpack(workdir)
+
+                with open(os.path.join(workdir, "git", filename)) as f:
+                    self.assertEqual(f.read(), content)
+
+        commit_1 = self.commit_file("a.mp3", "version 1")
+        commit_2 = self.commit_file("a.mp3", "version 2")
+
+        self.d.setVar('SRC_URI', "git://%s;protocol=file;lfs=1;branch=master" % self.srcdir)
+
+        # Seed the local download folder by fetching the latest commit and verifying that the LFS contents are
+        # available even when the upstream repository disappears.
+        fetch_and_verify(commit_2, "a.mp3", "version 2")
+        # Verify that even when an older revision is fetched, the needed LFS objects are fetched into the download
+        # folder.
+        fetch_and_verify(commit_1, "a.mp3", "version 1")
+
+    @skipIfNoGitLFS()
     @skipIfNoNetwork()
     def test_real_git_lfs_repo_succeeds_without_lfs_param(self):
         self.d.setVar('SRC_URI', "git://gitlab.com/gitlab-examples/lfs.git;protocol=https;branch=master")