Correct a problem whereby system packages already in the working set

may conflict with new eggs buildout is trying to install.

src/zc/buildout/easy_install.py

@@ -568,6 +568,9 @@ class Installer:
                         "Couldn't download distribution %s." % avail)
 
                 dists = [_move_to_eggs_dir_and_compile(dist, self._dest)]
+                for _d in dists:
+                    if _d not in ws:
+                        ws.add(_d, replace=True)
 
             finally:
                 if tmp != self._download_cache:
@@ -575,10 +578,14 @@ class Installer:
 
             self._env_rescan_dest()
             dist = self._env.best_match(requirement, ws)
+
             logger.info("Got %s.", dist)
 
         else:
             dists = [dist]
+            if dist not in ws:
+                ws.add(dist)
+
 
         if not self._install_from_cache and self._use_dependency_links:
             self._add_dependency_links_from_dists(dists)
@@ -635,8 +642,7 @@ class Installer:
                 pkg_resources.Requirement.parse('setuptools')
                 )
             if ws.find(requirement) is None:
-                for dist in self._get_dist(requirement, ws):
-                    ws.add(dist)
+                self._get_dist(requirement, ws)
 
     def _constrain(self, requirement):
         """Return requirement with optional [versions] constraint added."""
@@ -670,7 +676,6 @@ class Installer:
 
         for requirement in requirements:
             for dist in self._get_dist(requirement, ws):
-                ws.add(dist)
                 self._maybe_add_setuptools(ws, dist)
 
         # OK, we have the requested distributions and they're in the working
@@ -719,7 +724,6 @@ class Installer:
                     logger.debug('Adding required %r', str(req))
                 self._log_requirement(ws, req)
                 for dist in self._get_dist(req, ws):
-                    ws.add(dist)
                     self._maybe_add_setuptools(ws, dist)
             if dist not in req:
                 # Oops, the "best" so far conflicts with a dependency.

src/zc/buildout/easy_install.txt

@@ -125,8 +125,8 @@ The working set contains the distributions we retrieved.
 
     >>> for dist in ws:
     ...     print_(dist)
-    demo 0.2
     demoneeded 1.1
+    demo 0.2
 
 We got demoneeded because it was a dependency of demo.
 
@@ -169,8 +169,8 @@ The old setting is returned.
     ...     ['demo'], dest, links=[link_server], index=link_server+'index/')
     >>> for dist in ws:
     ...     print_(dist)
-    demo 0.4rc1
     demoneeded 1.2rc1
+    demo 0.4rc1
 
     >>> ls(dest)
     d  demo-0.2-py2.4.egg
@@ -195,9 +195,9 @@ dependencies.  We might do this to specify a specific version.
 
     >>> for dist in ws:
     ...     print_(dist)
-    demo 0.3
-    other 1.0
     demoneeded 1.0
+    other 1.0
+    demo 0.3
 
     >>> ls(dest)
     d  demo-0.2-py2.4.egg
@@ -231,8 +231,8 @@ Let's check that the uppercase dist is installed.
 
     >>> for dist in ws:
     ...     print_(dist)
-    MIXEDCASE 0.5
     demoneeded 1.1
+    MIXEDCASE 0.5
     >>> ls(dest)
     d  MIXEDCASE-0.5-pyN.N.egg
     d  demoneeded-1.1-py2.4.egg
@@ -256,7 +256,7 @@ then the versions numbers will be used.
     ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
     ...     versions = dict(demo='0.2', demoneeded='1.0'))
     >>> [d.version for d in ws]
-    ['0.2', '1.0']
+    ['1.0', '0.2']
 
 In this example, we specified a version for demoneeded, even though we
 didn't define a requirement for it.  The versions specified apply to
@@ -890,8 +890,8 @@ to pass a common base directory of the scripts and eggs:
     <BLANKLINE>
     import sys
     sys.path[0:0] = [
-      join(base, 'eggs/demo-0.3-pyN.N.egg'),
       join(base, 'eggs/demoneeded-1.1-pyN.N.egg'),
+      join(base, 'eggs/demo-0.3-pyN.N.egg'),
       '/ba',
       join(base, 'bar'),
       base,
@@ -924,13 +924,14 @@ We specified an interpreter and its paths are adjusted too:
     import sys
     <BLANKLINE>
     sys.path[0:0] = [
-      join(base, 'eggs/demo-0.3-pyN.N.egg'),
       join(base, 'eggs/demoneeded-1.1-pyN.N.egg'),
+      join(base, 'eggs/demo-0.3-pyN.N.egg'),
       '/ba',
       join(base, 'bar'),
       base,
       ]
     <BLANKLINE>
+    <BLANKLINE>
     _interactive = True
     if len(sys.argv) > 1:
         _options, _args = __import__("getopt").getopt(sys.argv[1:], 'ic:m:')

src/zc/buildout/tests.py

@@ -2018,8 +2018,8 @@ def bug_61890_file_urls_dont_seem_to_work_in_find_dash_links():
 
     >>> for dist in ws:
     ...     print_(dist)
-    demo 0.2
     demoneeded 1.1
+    demo 0.2
 
     >>> ls(dest)
     d  demo-0.2-py2.4.egg

src/zc/buildout/update.txt

@@ -87,8 +87,8 @@ Our buildout script has been updated to use the new eggs:
     <BLANKLINE>
     import sys
     sys.path[0:0] = [
-      '/sample-buildout/eggs/zc.buildout-99.99-py2.4.egg',
       '/sample-buildout/eggs/setuptools-99.99-py2.4.egg',
+      '/sample-buildout/eggs/zc.buildout-99.99-py2.4.egg',
       ]
     <BLANKLINE>
     import zc.buildout.buildout

zc.recipe.egg_/src/zc/recipe/egg/api.rst

@@ -89,9 +89,9 @@ of extra requirements to be included in the working set.
     Egg requirements:
     demo<0.3
     Working set:
-    demo 0.2
-    other 1.0
     demoneeded 1.1
+    other 1.0
+    demo 0.2
     extra paths: []
 
 We can see that the options were augmented with additional data