From 35e8acdb2d49f279862a99ea129a9bb260b0bc4a Mon Sep 17 00:00:00 2001
From: Ulf Magnusson <ulfalizer@gmail.com>
Date: Fri, 29 Sep 2017 02:10:55 +0200
Subject: Only invalidate defined symbols

Think I had it in the back of my head somewhere that not invalidating
undefined symbols could break some obscure cases, but turns out it's
perfectly safe: Nothing can change the value of an undefined symbol.
They always get their name as their value.

There's no need to unset user values on them either, because
set_user_value() already refuses to to set one on them.

Lets us get rid of the Python 2/3 compatibility hack and instead iterate
over a plain list of defined symbols.
---
 kconfiglib.py | 21 +++++++++++++++------
 tests/Kchain  |  3 +++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/kconfiglib.py b/kconfiglib.py
index 5e8426b..be10efb 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -132,9 +132,6 @@ class Config(object):
 
         # The set of all symbols, indexed by name (a string)
         self._syms = {}
-        # Python 2/3 compatibility hack. This is the only one needed.
-        self._syms_iter = self._syms.values if sys.version_info[0] >= 3 else \
-                          self._syms.itervalues
 
         # The set of all defined symbols in the configuration in the order they
         # appear in the Kconfig files. This excludes the special symbols n, m,
@@ -576,7 +573,12 @@ class Config(object):
     def unset_user_values(self):
         """Resets the values of all symbols, as if Config.load_config() or
         Symbol.set_user_value() had never been called."""
-        for sym in self._syms_iter():
+
+        # set_user_value() already rejects undefined symbols, and they don't
+        # need to be invalidated (because their value never changes), so we can
+        # just iterate over defined symbols.
+
+        for sym in self._kconfig_syms:
             # We're iterating over all symbols already, so no need for symbols
             # to invalidate their dependent symbols
             sym._unset_user_value_no_recursive_invalidate()
@@ -1595,7 +1597,12 @@ class Config(object):
         #    (these won't be included in _dep as that makes the dependency
         #    graph unwieldy, but Symbol._get_dependent() will include them)
         #  - Any symbols in a choice statement that depends on the symbol
-        for sym in self._syms_iter():
+
+        # Only calculate _dep for defined symbols. Undefined symbols could
+        # theoretically be selected/implied, but it wouldn't change their value
+        # (they always evaluate to their name), so it's not a true dependency.
+
+        for sym in self._kconfig_syms:
             for _, e in sym._prompts:
                 add_expr_deps(e, sym)
 
@@ -1664,7 +1671,9 @@ class Config(object):
         return rec(expr)
 
     def _invalidate_all(self):
-        for sym in self._syms_iter():
+        # Undefined symbols never change value and don't need to be
+        # invalidated, so we can just iterate over defined symbols
+        for sym in self._kconfig_syms:
             sym._invalidate()
 
     #
diff --git a/tests/Kchain b/tests/Kchain
index 643a949..d742c9e 100644
--- a/tests/Kchain
+++ b/tests/Kchain
@@ -75,6 +75,9 @@ config CHAIN_IMPLY_RELAY
     default y
     imply CHAIN_18 if CHAIN_17
 
+config CHAIN_18
+    tristate "chain 19"
+
 if CHAIN_18 = 0
 config CHAIN_19
     tristate "chain 19"
-- 
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