[feat] Add support for escaping $ with $$

src/zc/buildout/buildout.py

@@ -58,6 +58,7 @@ import sys
 import tempfile
 import zc.buildout
 import zc.buildout.download
+from functools import partial
 
 PY3 = sys.version_info[0] == 3
 if PY3:
@@ -833,7 +834,7 @@ class Buildout(DictMixin):
             if part in install_parts:
                 old_options = installed_part_options[part].copy()
                 installed_files = old_options.pop('__buildout_installed__')
-                new_options = self.get(part)
+                new_options = self.get(part).copy()
                 if old_options == new_options:
                     # The options are the same, but are all of the
                     # installed files still there?  If not, we should
@@ -1575,12 +1576,16 @@ class Options(DictMixin):
     def _dosub(self, option, v):
         __doing__ = 'Getting option %s:%s.', self.name, option
         seen = [(self.name, option)]
-        v = '$$'.join([self._sub(s, seen) for s in v.split('$$')])
+        v = '$$'.join([self._sub(s, seen, last=False)
+                       for s in v.split('$$')])
         self._cooked[option] = v
 
-    def get(self, option, default=None, seen=None):
+    def get(self, option, default=None, seen=None, last=True):
         try:
-            return self._data[option]
+            if last:
+                return self._data[option].replace('$${', '${')
+            else:
+                return self._data[option]
         except KeyError:
             pass
 
@@ -1602,16 +1607,20 @@ class Options(DictMixin):
                     )
             else:
                 seen.append(key)
-            v = '$$'.join([self._sub(s, seen) for s in v.split('$$')])
+            v = '$$'.join([self._sub(s, seen, last=False)
+                           for s in v.split('$$')])
             seen.pop()
 
         self._data[option] = v
-        return v
+        if last:
+            return v.replace('$${', '${')
+        else:
+            return v
 
     _template_split = re.compile('([$]{[^}]*})').split
     _simple = re.compile('[-a-zA-Z0-9 ._]+$').match
     _valid = re.compile(r'\${[-a-zA-Z0-9 ._]*:[-a-zA-Z0-9 ._]+}$').match
-    def _sub(self, template, seen):
+    def _sub(self, template, seen, last=True):
         value = self._template_split(template)
         subs = []
         for ref in value[1::2]:
@@ -1639,7 +1648,7 @@ class Options(DictMixin):
             section, option = s
             if not section:
                 section = self.name
-            v = self.buildout[section].get(option, None, seen)
+            v = self.buildout[section].get(option, None, seen, last=last)
             if v is None:
                 if option == '_buildout_section_name_':
                     v = self.name
@@ -1652,11 +1661,6 @@ class Options(DictMixin):
         return ''.join([''.join(v) for v in zip(value[::2], subs)])
 
     def __getitem__(self, key):
-        try:
-            return self._data[key]
-        except KeyError:
-            pass
-
         v = self.get(key)
         if v is None:
             raise MissingOption("Missing option: %s:%s" % (self.name, key))
@@ -1768,10 +1772,12 @@ def _save_option(option, value, f):
 
 def _save_options(section, options, f):
     print_('[%s]' % section, file=f)
-    items = list(options.items())
-    items.sort()
-    for option, value in items:
-        _save_option(option, value, f)
+    if isinstance(options, Options):
+        get_option = partial(options.get, last=False)
+    else:
+        get_option = options.get
+    for option in sorted(options):
+        _save_option(option, get_option(option), f)
 
 def _default_globals():
     """Return a mapping of default and precomputed expressions.

src/zc/buildout/tests/test_all.py

@@ -1181,6 +1181,8 @@ Uninstall recipes need to be called when a part is removed too:
     uninstalling
     Installing demo.
     installing
+    Section `demo` contains unused option(s): 'x'.
+    This may be an indication for either a typo in the option's name or a bug in the used recipe.
 
 
     >>> write('buildout.cfg', '''
@@ -2924,6 +2926,73 @@ def increment_on_command_line():
       recipe='zc.buildout:debug'
     """
 
+def bug_664539_simple_buildout():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = $${nonexistent:option}
+  ... ''')
+
+  >>> print_(system(buildout), end='')
+  Installing escape.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
+def bug_664539_reference():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = ${:bar}
+  ... bar = $${nonexistent:option}
+  ... ''')
+
+  >>> print_(system(buildout), end='')
+  Installing escape.
+    bar='${nonexistent:option}'
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
+def bug_664539_complex_buildout():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = ${level1:foo}
+  ...
+  ... [level1]
+  ... recipe = zc.buildout:debug
+  ... foo = ${level2:foo}
+  ...
+  ... [level2]
+  ... recipe = zc.buildout:debug
+  ... foo = $${nonexistent:option}
+  ... ''')
+
+  >>> print_(system(buildout), end='')
+  Installing level2.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  Installing level1.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  Installing escape.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
 def test_constrained_requirement():
     """
     zc.buildout.easy_install._constrained_requirement(constraint, requirement)