bitbake: git: Allow local repos to use HEAD

Introduce a new 'usehead' url parameter for git repositories. Specifying
usehead=1 causes bitbake to use whatever commit the repository HEAD is
pointing to. Usage of usehead=1 is only allowed for local git
repositories, i.e. it must always be accompanied with protocol=file url
parameter.

[YOCTO #9351]

(Bitbake rev: 2673fac5a9d06de937101e3fb2ddf1e60ff99abf)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/git.py

@@ -49,6 +49,10 @@ Supported SRC_URI options are:
    referring to commit which is valid in tag instead of branch.
    The default is "0", set nobranch=1 if needed.
 
+- usehead
+   For local git:// urls to use the current branch HEAD as the revsion for use with
+   AUTOREV. Implies nobranch.
+
 """
 
 #Copyright (C) 2005 Richard Purdie
@@ -153,6 +157,13 @@ class Git(FetchMethod):
 
         ud.nobranch = ud.parm.get("nobranch","0") == "1"
 
+        # usehead implies nobranch
+        ud.usehead = ud.parm.get("usehead","0") == "1"
+        if ud.usehead:
+            if ud.proto != "file":
+                 raise bb.fetch2.ParameterError("The usehead option is only for use with local ('protocol=file') git repositories", ud.url)
+            ud.nobranch = 1
+
         # bareclone implies nocheckout
         ud.bareclone = ud.parm.get("bareclone","0") == "1"
         if ud.bareclone:
@@ -168,6 +179,9 @@ class Git(FetchMethod):
             ud.branches[name] = branch
             ud.unresolvedrev[name] = branch
 
+        if ud.usehead:
+            ud.unresolvedrev['default'] = 'HEAD'
+
         ud.basecmd = data.getVar("FETCHCMD_git", d, True) or "git -c core.fsyncobjectfiles=0"
 
         ud.write_tarballs = ((data.getVar("BB_GENERATE_MIRROR_TARBALLS", d, True) or "0") != "0") or ud.rebaseable
@@ -387,7 +401,7 @@ class Git(FetchMethod):
         """
         output = self._lsremote(ud, d, "")
         # Tags of the form ^{} may not work, need to fallback to other form
-        if ud.unresolvedrev[name][:5] == "refs/":
+        if ud.unresolvedrev[name][:5] == "refs/" or ud.usehead:
             head = ud.unresolvedrev[name]
             tag = ud.unresolvedrev[name]
         else: