Don't write out 'option env' symbols to C header

Oversight. SYMBOL_AUTO (env_var) being set indirectly clears
SYMBOL_WRITE (_write_to_conf) in sym_calc_value(). The .config case was
already fine due to an explicit env_var check.

Even non-visible env. symbols ended up in the header, due to
'option env' internally adding a default.

Disallow user values altogether on 'option env' symbols, even if
specified manually. This matches the C implementation. Add a warning
too.

1 files changed, 10 insertions, 4 deletions

diff --git a/kconfiglib.py b/kconfiglib.py
index f31a71c..05cc172 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -2474,6 +2474,10 @@ class Symbol(object):
                         val = val_expr.str_value
                         break
 
+        # Corresponds to SYMBOL_AUTO in the C implementation
+        if self.env_var is not None:
+            self._write_to_conf = False
+
         self._cached_str_val = val
         return val
 
@@ -2572,10 +2576,6 @@ class Symbol(object):
         """
         See the class documentation.
         """
-        if self.env_var is not None:
-            # Corresponds to SYMBOL_AUTO being set in the C implementation
-            return None
-
         # Note: _write_to_conf is determined when the value is calculated. This
         # is a hidden function call due to property magic.
         val = self.str_value
@@ -2666,6 +2666,12 @@ class Symbol(object):
 
             return False
 
+        if self.env_var is not None:
+            self.kconfig._warn("ignored attempt to assign user value to "
+                               "{}, which gets its value from the environment"
+                               .format(self.name))
+            return False
+
         if self.choice and value == 2:
             # Remember this as a choice selection only. Makes switching back
             # and forth between choice modes work as expected, and makes the