gitclone: revision has priority over branch

Both are compatible.

README.rst

@@ -148,7 +148,7 @@ Specific revision
 -----------------
 
 You can specify a specific commit hash or tag using `revision` option.
-This option is not compatible with "branch" option::
+This option has priority over the "branch" option::
 
   >>> cd(sample_buildout)
   >>> write(sample_buildout, 'buildout.cfg',
@@ -222,6 +222,37 @@ extend an existing section specifying a branch)::
   >>> print system('git branch')
   * master
 
+Revision/branch priority
+------------------------
+
+If both revision and branch parameters are set, revision parameters is used
+and branch parameter is ignored::
+
+  >>> cd(sample_buildout)
+  >>> write(sample_buildout, 'buildout.cfg',
+  ... """
+  ... [buildout]
+  ... parts = git-clone
+  ...
+  ... [git-clone]
+  ... recipe = slapos.recipe.build:gitclone
+  ... repository = http://git.erp5.org/repos/slapos.recipe.build.git
+  ... branch = mybranch
+  ... revision = 2566127
+  ... """)
+
+  >>> print system(buildout)
+  Uninstalling git-clone.
+  Running uninstall recipe.
+  Installing git-clone.
+  Warning: "branch" parameter with value "mybranch" is ignored. Checking out to revision 2566127...
+  Cloning into '/sample-buildout/parts/git-clone'...
+  HEAD is now at 2566127 ...
+
+  >>> cd(sample_buildout, 'parts', 'git-clone')
+  >>> print system('git branch')
+  * master
+
 Specific git binary
 -------------------
 

slapos/recipe/gitclone.py

@@ -28,6 +28,7 @@
 import hashlib
 import os
 import shutil
+import sys
 import time
 import traceback
 
@@ -146,9 +147,9 @@ class Recipe(object):
     if not self.repository:
       raise UserError('repository parameter is mandatory.')
     if self.revision and self.branch:
-      # revision and branch options are incompatible
-      raise UserError('revision and branch (other than master) parameters '
-          'are set but are incompatible. Please specify only one of them.')
+      # revision option has priority over branch option
+      self.branch_overrided = self.branch
+      self.branch = None
 
     # Check existence of directory
     if not os.path.exists(self.location):
@@ -180,6 +181,13 @@ class Recipe(object):
         # If develop is set, assume that this is a valid working copy
         return [self.location]
 
+    if getattr(self, 'branch_overrided', None):
+      print('Warning: "branch" parameter with value "%s" is ignored. '
+            'Checking out to revision %s.' % (
+            self.branch_overrided, self.revision)
+      )
+      sys.stdout.flush()
+
     git_clone_command = [self.git_command, 'clone',
                 self.repository,
                 self.location]