[feat] Add setup-eggs option in zc.recipe.egg:custom.

src/zc/buildout/easy_install.py

@@ -1796,7 +1796,12 @@ def call_pip_install(spec, dest):
 
     env = os.environ.copy()
     python_path = pip_path[:]
-    python_path.append(env.get('PYTHONPATH', ''))
+    env_paths = env.get('PYTHONPATH')
+    if env_paths:
+        python_path.append(env_paths)
+    extra_env_path = env.get('PYTHONEXTRAPATH')
+    if extra_env_path:
+        python_path.append(extra_env_path)
     env['PYTHONPATH'] = os.pathsep.join(python_path)
 
     if level <= logging.DEBUG:

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

@@ -83,6 +83,23 @@ class Custom(Base):
 
         distribution = options.get('egg', options.get('eggs', self.name)
                                    ).strip()
+
+        setup_eggs = [
+            r.strip()
+            for r in options.get('setup-eggs', '').split('\n')
+            if r.strip()]
+        if setup_eggs:
+            ws = zc.buildout.easy_install.install(
+                setup_eggs, options['_e'],
+                links=self.links,
+                index=self.index,
+                executable=sys.executable,
+                path=[options['_d'], options['_e']],
+                newest=self.newest,
+                )
+            extra_path = os.pathsep.join(ws.entries)
+            self.environment['PYTHONEXTRAPATH'] = os.environ['PYTHONEXTRAPATH'] = extra_path
+
         self._set_environment()
         try:
             return zc.buildout.easy_install.build(

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

@@ -20,6 +20,10 @@ rpath
    A new-line separated list of directories to search for dynamic libraries
    at run time.
 
+setup-eggs
+   A new-line separated list of eggs that need to be installed
+   beforehand. It is useful to meet the `setup_requires` requirement.
+
 define
    A comma-separated list of names of C preprocessor variables to
    define.