Always detect missing extras, and let buildout exit cleanly if we find them.

Also add the required changes to zc.recipe.egg.

src/zc/buildout/easy_install.py

@@ -736,7 +736,7 @@ class Installer(object):
                     pkg_resources.VersionConflict(dist, req), ws)
 
             best[req.key] = dist
-            if self._allow_unknown_extras:
+
             missing_requested = sorted(
                 set(req.extras) - set(dist.extras)
             )
@@ -745,11 +745,20 @@ class Installer(object):
                     '%s does not provide the extra \'%s\'',
                     dist, missing
                 )
+
+            if missing_requested:
+                if not self._allow_unknown_extras:
+                    raise zc.buildout.UserError(
+                        "Couldn't find the required extras. Add 'allow-unknown-extras=true' "
+                        "to the [buildout] configuration if this is acceptable."
+                    )
+
                 extra_requirements = sorted(
                     set(dist.extras) & set(req.extras)
                 )
             else:
                 extra_requirements = dist.requires(req.extras)[::-1]
+
             for extra_requirement in extra_requirements:
                 self._requirements_and_constraints.append(
                     "Requirement of %s: %s" % (

src/zc/buildout/easy_install.txt

@@ -225,7 +225,7 @@ is an error.
     ...     index=link_server+'index/')
     Traceback (most recent call last):
     ...
-    UnknownExtra: demo 0.3 has no such extra feature 'unknown_extra'
+    UserError: Couldn't find the required extras. Add 'allow-unknown-extras=true' to the [buildout] configuration if this is acceptable.
 
 We can pass the ``allow_unknown_extras`` argument to force the
 installation to proceed.

src/zc/buildout/tests.py

@@ -3730,8 +3730,6 @@ def test_suite():
                 (re.compile(r'\\[\\]?'), '/'),
                 (re.compile('(\n?)-  ([a-zA-Z_.-]+)\n-  \\2.exe\n'),
                  '\\1-  \\2\n'),
-                (re.compile(r'^(\w+\.)*(UnknownExtra: )'),
-                 '\2'),
                ]+(sys.version_info < (2, 5) and [
                   (re.compile('.*No module named runpy.*', re.S), ''),
                   (re.compile('.*usage: pdb.py scriptfile .*', re.S), ''),

zc.recipe.egg_/src/zc/recipe/egg/egg.py

@@ -23,6 +23,8 @@ import re
 import sys
 import zc.buildout.easy_install
 
+from zc.buildout.buildout import bool_option
+
 
 class Eggs(object):
 
@@ -82,6 +84,7 @@ class Eggs(object):
             links=self.links,
             index=self.index,
             allow_hosts=self.allow_hosts,
+            allow_unknown_extras=bool_option(buildout['buildout'], 'allow-unknown-extras')
             )
 
         return orig_distributions, ws
@@ -127,6 +130,7 @@ class Eggs(object):
         links=(),
         index=None,
         allow_hosts=('*',),
+        allow_unknown_extras=False,
     ):
         """Helper function to build a working set.
 
@@ -145,6 +149,7 @@ class Eggs(object):
             tuple(links),
             index,
             tuple(allow_hosts),
+            allow_unknown_extras,
         )
         if cache_key not in cache_storage:
             if offline:
@@ -159,7 +164,8 @@ class Eggs(object):
                     index=index,
                     path=[develop_eggs_dir],
                     newest=newest,
-                    allow_hosts=allow_hosts)
+                    allow_hosts=allow_hosts,
+                    allow_unknown_extras=allow_unknown_extras)
             ws = self._sort_working_set(ws)
             cache_storage[cache_key] = ws