bitbake: fetch/git: Avoid clean upon failure

Currently when git fetches fail, it destroys all the existing local clone data.
For large repositories this can introduce long build delays when for example,
you just typo'd the git revision hash.

The git fetcher should be able to recover most directories so when the fetch is
for a git repo, avoid removing things unless clean is explicitly called
(e.g. a -c cleanall task).

(Bitbake rev: 1b3cd039fe19b24bd4be9a0202a98cdcbb0e9443)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -1115,7 +1115,8 @@ def try_mirror_url(fetch, origud, ud, ld, check = False):
             logger.debug("Mirror fetch failure for url %s (original url: %s)" % (ud.url, origud.url))
             logger.debug(str(e))
         try:
-            ud.method.clean(ud, ld)
+            if ud.method.cleanup_upon_failure():
+                ud.method.clean(ud, ld)
         except UnboundLocalError:
             pass
         return False
@@ -1440,6 +1441,12 @@ class FetchMethod(object):
         """
         return False
 
+    def cleanup_upon_failure(self):
+        """
+        When a fetch fails, should clean() be called?
+        """
+        return True
+
     def verify_donestamp(self, ud, d):
         """
         Verify the donestamp file
@@ -1885,7 +1892,7 @@ class Fetch(object):
                             logger.debug(str(e))
                         firsterr = e
                         # Remove any incomplete fetch
-                        if not verified_stamp:
+                        if not verified_stamp and m.cleanup_upon_failure():
                             m.clean(ud, self.d)
                         logger.debug("Trying MIRRORS")
                         mirrors = mirror_from_string(self.d.getVar('MIRRORS'))

bitbake/lib/bb/fetch2/git.py

@@ -150,6 +150,9 @@ class Git(FetchMethod):
     def supports_checksum(self, urldata):
         return False
 
+    def cleanup_upon_failure(self):
+        return False
+
     def urldata_init(self, ud, d):
         """
         init git specific variable within url data