bitbake: fetch2: Ensure a valid symlink in PREMIRRORS case when using shallow cloning

- Since `ud.path` contains in that case the `PREMIRRORS` prefix path,
  this change ensures that a correct symlink is set up.

(Bitbake rev: 37ed18e45aa17406162efc5ee3ddb2d6b33d07b9)

Signed-off-by: Stefan Koch <stefan-koch@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/git.py

@@ -348,6 +348,13 @@ class Git(FetchMethod):
     def tarball_need_update(self, ud):
         return ud.write_tarballs and not os.path.exists(ud.fullmirror)
 
+    def update_mirror_links(self, ud, origud):
+        super().update_mirror_links(ud, origud)
+        # When using shallow mode, add a symlink to the original fullshallow
+        # path to ensure a valid symlink even in the `PREMIRRORS` case
+        if ud.shallow and not os.path.exists(origud.fullshallow):
+            self.ensure_symlink(ud.localpath, origud.fullshallow)
+
     def try_premirror(self, ud, d):
         # If we don't do this, updating an existing checkout with only premirrors
         # is not possible