Allow for passing in previously compiled grains to custom grain modules

Closes #47338

doc/topics/grains/index.rst

@@ -269,6 +269,11 @@ grain will override that core grain. Similarly, grains from
 ``/etc/salt/minion`` override both core grains and custom grain modules, and
 grains in ``_grains`` will override *any* grains of the same name.
 
+For custom grains, if the function takes an argument ``grains``, then the
+previously rendered grains will be passed in.  Because the rest of the grains
+could be rendered in any order, the only grains that can be relied upon to be
+passed in are ``core`` grains. This was added in the Fluorine Release.
+
 
 Examples of Grains
 ==================

doc/topics/releases/fluorine.rst

@@ -5,6 +5,16 @@ Salt Release Notes - Codename Fluorine
 ======================================
 
 
+Grains Dictionary Passed into Custom Grains
+-------------------------------------------
+
+Starting in this release, if a custom grains function accepts a variable named
+``grains``, the Grains dictionary of the already compiled grains will be passed
+in.  Because of the non deterministic order that grains are rendered in, the
+only grains that can be relied upon to be passed in are ``core.py`` grains,
+since those are compiled first.
+
+
 "Virtual Package" Support Dropped for APT
 -----------------------------------------
 

salt/loader.py

@@ -751,8 +751,14 @@ def grains(opts, force_refresh=False, proxy=None):
             # proxymodule for retrieving information from the connected
             # device.
             log.trace('Loading %s grain', key)
-            if funcs[key].__code__.co_argcount == 1:
-                ret = funcs[key](proxy)
+            parameters = list(funcs[key].__code__.co_varnames)
+            if funcs[key].__code__.co_argcount > 0:
+                kwargs = {}
+                if 'proxy' in parameters:
+                    kwargs['proxy'] = proxy
+                if 'grains' in parameters:
+                    kwargs['grains'] = grains_data
+                ret = funcs[key](**kwargs)
             else:
                 ret = funcs[key]()
         except Exception:

tests/integration/files/file/base/_grains/test_custom_grains.py

@@ -0,0 +1,4 @@
+def test(grains):
+    if 'os' in grains:
+        return {'custom_grain_test': 'itworked'}
+    return {'custom_grain_test': 'itdidntwork'}

tests/integration/grains/test_custom.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+'''
+Test the core grains
+'''
+
+# Import python libs
+from __future__ import absolute_import, unicode_literals
+
+# Import Salt Testing libs
+from tests.support.case import ModuleCase
+
+
+class TestGrainsCore(ModuleCase):
+    '''
+    Test the core grains grains
+    '''
+
+    def test_grains_passed_to_custom_grain(self):
+        '''
+        test if current grains are passed to grains module functions that have a grains argument
+        '''
+        self.assertEqual(self.run_function('grains.get', ['custom_grain_test']), 'itworked')