Add option to pin setuptools version

bootstrap/bootstrap.py

@@ -59,6 +59,7 @@ parser.add_option("-f", "--find-links",
 parser.add_option("--allow-site-packages",
                   action="store_true", default=False,
                   help=("Let bootstrap.py use existing site packages"))
+parser.add_option("--setuptools-version", help="use a specific setuptools version")
 
 
 options, args = parser.parse_args()
@@ -89,6 +90,10 @@ if not options.allow_site_packages:
             sys.path[:] = [x for x in sys.path if sitepackage_path not in x]
 
 setup_args = dict(to_dir=tmpeggs, download_delay=0)
+
+if not options.setuptools_version is None:
+    setup_args['version'] = options.setuptools_version
+
 ez['use_setuptools'](**setup_args)
 import setuptools
 import pkg_resources

src/zc/buildout/bootstrap.txt

@@ -89,3 +89,41 @@ Let's make sure the generated `buildout` script uses it::
       '/sample/eggs/setuptools-...egg',
       '/sample/eggs/zc.buildout-2.0.0...egg',
       ]...
+
+Now trying the `--setuptools-version` option, that let you define a version for
+`setuptools`.
+
+Now let's try with `5.3`, which happens to exist::
+
+    >>> print_('X'); print_(system(
+    ...     zc.buildout.easy_install._safe_arg(sys.executable)+' '+
+    ...     'bootstrap.py --setuptools-version 5.3')); print_('X')
+    ... # doctest: +ELLIPSIS
+    X...Generated script '/sample/bin/buildout'...X
+
+Let's make sure the generated `buildout` script uses it::
+
+    >>> print_(open(buildout_script).read()) # doctest: +ELLIPSIS
+    #...
+    sys.path[0:0] = [
+      '/sample/eggs/setuptools-5.3...egg',
+      '/sample/eggs/zc.buildout-...egg',
+      ]...
+
+Now let's try specifying both `zc.buildout` and `setuptools` to versions
+which happens to exist::
+
+    >>> print_('X'); print_(system(
+    ...     zc.buildout.easy_install._safe_arg(sys.executable)+' '+
+    ...     'bootstrap.py --setuptools-version 5.3 --version 2.0.0')); print_('X')
+    ... # doctest: +ELLIPSIS
+    X...Generated script '/sample/bin/buildout'...X
+
+Let's make sure the generated `buildout` script uses it::
+
+    >>> print_(open(buildout_script).read()) # doctest: +ELLIPSIS
+    #...
+    sys.path[0:0] = [
+      '/sample/eggs/setuptools-5.3...egg',
+      '/sample/eggs/zc.buildout-2.0.0...egg',
+      ]...