Let buildout run a script to create a constraints file. [5.2]

core.cfg

@@ -19,15 +19,10 @@ allow-hosts =
 find-links += http://dist.plone.org/thirdparty/
 
 extensions =
-    buildout.requirements
 # Keep mr.developer as last one, because some jenkins scripts look for
 # this and add a git-clone-depth after it.
     mr.developer
 
-# write a constraints file
-dump-requirements-file = ${buildout:directory}/constraints.txt
-overwrite-requirements-file = true
-
 # require picked versions
 show-picked-versions = true
 allow-picked-versions = false
@@ -53,6 +48,7 @@ plone-user =
 
 [buildout:python27]
 parts =
+    constraints
     instance
     instance-archetypes
     zopepy
@@ -67,6 +63,7 @@ extensions +=
 
 [buildout:python3]
 parts =
+    constraints
     instance
     zopepy
     ploneversioncheck
@@ -158,3 +155,8 @@ recipe = zc.recipe.egg
 eggs =
     zodbupdate
     ${instance:eggs}
+
+[constraints]
+recipe = plone.recipe.command
+command = bin/python create-constraints.py
+update-command = ${:command}

create-constraints.py

@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+"""
+Parse versions from buildout.cfg and write them into constraints.txt.
+This script is automatically called by buildout.
+
+Manual usage: bin/python create-constraints.py
+zc.buildout needs to be importable in that python.
+"""
+from zc.buildout import buildout
+
+
+# We could read a buildout config filename from the command line arguments,
+# but for now it is fine to hardcode it:
+configfile = "buildout.cfg"
+config = buildout.Buildout(configfile, [])
+
+# Get the constraints from the version pins.
+# Nice: the versions get set directly on the config.
+# Note: this works like a dictionary, but is a class 'zc.buildout.buildout.Options'.
+versions = config.versions
+constraints_file = "constraints.txt"
+with open(constraints_file, "w") as cfile:
+    cfile.write("# File created by {}\n".format(__file__))
+    cfile.write("# Constraints parsed from {}\n".format(configfile))
+    for package, version in sorted(versions.items()):
+        cfile.write("{}=={}\n".format(package, version))
+print("Wrote all versions as constraints to {}.".format(constraints_file))

tests.cfg

@@ -173,6 +173,7 @@ oauthlib = 3.1.0
 pathtools = 0.1.2
 pdbpp = 0.10.2
 pkginfo = 1.5.0.1
+plone.recipe.command = 1.1
 progress = 1.5
 prompt-toolkit = 1.0.18
 pycparser = 2.19