ZODB: Provide ZODB4-wc2 which backports MVCC approach from ZODB5

To always call loadBefore instead of load.
Wendelin.core 2 needs this - see nexedi/ZODB@8e7eab33 for details.

There is also ZEO4-wc2 which contains backports of ZEO5 patches that are
needed for wendelin.core 2 to work correctly.

Wendelin.core 2 will work with ZODB4-wc2 or ZODB5.
Wendelin.core 2 will not work with just ZODB4.

component/ZEO/buildout.cfg

@@ -68,3 +68,13 @@ egg_versions =
   ZEO = 5.2.2
   trollius = 2.2.post1
   futures = 3.2.0
+
+
+# ZEO4-wc2 is ZEO4 version with patches for wendelin.core 2 to work correctly.
+# The patches are backports of what is in ZEO master (ZEO5), but since upstream
+# considers 4 branch to be "dead", we have to maintain it by ourselves.
+# See https://github.com/zopefoundation/ZEO/pull/161 for the reference.
+[ZEO4-wc2]
+<= ZEO4
+revisions = bf80d23d3506
+location = ${buildout:parts-directory}/ZEO4-wc2

component/ZODB/buildout.cfg

@@ -9,7 +9,7 @@ extends =
 parts = ZODB/scripts
 
 
-# ZODB allows to use either ZODB4 or ZODB5.
+# ZODB allows to use either ZODB4, ZODB4-wc2 or ZODB5.
 # To select which version to use users should do:
 #
 #   [ZODB]
@@ -62,6 +62,24 @@ egg_versions =
   transaction = 2.4.0
 
 
+# ZODB4-wc2 is ZODB4 version with patches for wendelin.core 2 to work correctly.
+# The main change is backport of the way MVCC is handled by always calling
+# loadBefore instead of load.
+# See https://lab.nexedi.com/nexedi/ZODB/commit/8e7eab33 for details.
+[ZODB4-wc2]
+<= ZODB4
+recipe = zc.recipe.egg:develop
+setup = ${ZODB4-wc2-repository:location}
+
+[ZODB4-wc2-repository]
+recipe  = slapos.recipe.build:gitclone
+repository = https://lab.nexedi.com/nexedi/ZODB.git
+git-executable = ${git:location}/bin/git
+branch = 4-nxd+MVCC-load-before
+revision = 4.4.5-9-g8e7eab330
+location = ${buildout:parts-directory}/ZODB4-wc2
+
+
 # XXX: buildout fails to install properly eggs with setup_requires
 [BTrees]
 recipe = zc.recipe.egg:custom

component/ZODB/test-zodb4-wc2.cfg

+# SlapOS software release to test ZODB4-wc2 on Nexedi testing infrastructure.
+
+[buildout]
+extends =
+# test<X>.cfg configures ZODB.major=<X>.
+
+    ../../stack/nxdtest.cfg
+    ../pygolang/buildout.cfg
+    ../python-manuel/buildout.cfg
+    buildout.cfg
+    ../ZEO/buildout.cfg
+
+parts =
+    ZODB
+    .nxdtest
+
+#   for instance
+    ZODB-python
+    slapos-cookbook
+    instance.cfg
+
+[ZODB]
+major = 4-wc2
+[ZODB4-wc2-repository]
+revision =
+
+# we need persistent to be a git checkout because persistent tests want to
+# discover in-tree files that are not present in persistent egg when it is
+# installed in non-development mode:
+#
+#   https://erp5.nexedi.net/test_result_module/20201123-3F859E35/7
+#   (look for "AssertionError: could not find my setup.py")
+#
+#   https://github.com/zopefoundation/persistent/blob/4.6.4-0-g7ed95cf/persistent/tests/test_docs.py#L37-L43
+[persistent]
+recipe = zc.recipe.egg:develop
+setup = ${persistent-repository:location}
+
+[persistent-repository]
+recipe  = slapos.recipe.build:gitclone
+location = ${buildout:parts-directory}/persistent
+repository = https://github.com/zopefoundation/persistent.git
+branch = master
+revision = 4.6.4-0-g7ed95cf
+git-executable = ${git:location}/bin/git
+
+
+# test-dependent eggs that must come through in-tree recipes.
+[ZODB]
+depends += ${manuel:egg}
+
+
+# bin/python is preinstalled with sys.path to ZODB & friends.
+[ZODB-python]
+<= python-interpreter
+eggs +=
+  ${ZODB:egg}[test]
+  ${ZEO:egg}[test]
+  transaction[test]
+
+# env.sh for ZODB's python to be on $PATH.
+[ZODB-env.sh]
+recipe   = slapos.recipe.template:jinja2
+rendered = ${buildout:directory}/${:_buildout_section_name_}
+template = inline:
+  export PS1="(ZODB-env) $PS1"
+  export PATH=${buildout:bin-directory}:$PATH
+
+# .nxdtest to run ZODB tests
+[.nxdtest]
+<= jinja2-template
+template =
+  inline:
+  # determine where ZODB & friends were installed
+  from subprocess import check_output
+  _ = check_output(['python', '-c', """if 1:
+        from os.path import dirname
+        def X(mod):
+            m=__import__(mod)
+            print(dirname(m.__file__))
+        X("ZODB"); X("persistent"); X("BTrees"); X("transaction"), X("ZEO")
+  """])
+  ZODB, persistent, BTrees, transaction, ZEO = _.split()
+
+  # run tests for whole ZODB stack
+  TestCase('ZODB/unit',       ['python', '-m', 'zope.testrunner', '-uv', '--package-path', ZODB, 'ZODB'])
+  TestCase('ZODB/functional', ['python', '-m', 'zope.testrunner', '-fv', '--package-path', ZODB, 'ZODB'])
+
+  TestCase('ZEO/unit',       ['python', '-m', 'zope.testrunner', '-uv', '--package-path', ZEO, 'ZEO'])
+  TestCase('ZEO/functional', ['python', '-m', 'zope.testrunner', '-fv', '--package-path', ZEO, 'ZEO'])
+
+  TestCase('persistent', ['python', '-m', 'zope.testrunner', '-v', '--package-path', persistent, 'persistent'])
+  TestCase('BTrees',     ['python', '-m', 'zope.testrunner', '-v', '--package-path', BTrees, 'BTrees'])
+
+  # transaction uses unittest instead of zope.testrunner
+  import os.path
+  def P(path): return os.path.join(path, '..')
+  TestCase('transaction',['python', '-m', 'unittest', 'discover', '-s', P(transaction)])
+
+
+# instance to run nxdtest.
+[instance.cfg]
+<= jinja2-template
+template = inline:
+  [buildout]
+  extends = ${nxdtest-instance.cfg:rendered}
+
+  [runTestSuite]
+  env.sh  = ${ZODB-env.sh:rendered}
+  workdir = ${buildout:directory}
+
+
+[versions]
+mock = 3.0.5
+random2 = 1.0.1
+zope.testing = 4.7
+zope.testrunner = 5.2
+zope.exceptions = 4.4