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.

3 files changed, 36 insertions, 6 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
diff --git a/tests/Kmisc b/tests/Kmisc
index 44fdfdc..9da57a4 100644
--- a/tests/Kmisc
+++ b/tests/Kmisc
@@ -61,12 +61,18 @@ menu "menu"
 endmenu
 
 config FROM_ENV
-    string
+    string "from env"
     option env="ENV_VAR"
 
 config FROM_ENV_MISSING
-    string
+    string "from env missing"
     option env="MISSING_ENV_VAR"
+    default "missing"
+
+config FROM_ENV_WEIRD
+    string
+    default "weird"
+    option env="ENV_VAR"
 
 config NOT_ALLNOCONFIG_Y
     bool "not allnoconfig_y"
diff --git a/testsuite.py b/testsuite.py
index e7168a6..932ee6a 100644
--- a/testsuite.py
+++ b/testsuite.py
@@ -1233,6 +1233,24 @@ g
                format(s.name))
 
 
+    print("Testing 'option env' semantics")
+
+    os.environ["ENV_VAR"] = "ENV_VAR value"
+
+    # References undefined env. var. and tries to assign 'option env' variable,
+    # so disable warnings
+    c = Kconfig("Kconfiglib/tests/Kmisc", warn=False)
+
+    # Verify that 'option env' symbols can't be assigned user values, and that
+    # 'option env' is treated like a default
+    assign_and_verify_user_value("FROM_ENV", "foo", None, False)
+    assign_and_verify_user_value("FROM_ENV_MISSING", "foo", None, False)
+    verify_value("FROM_ENV", "ENV_VAR value")
+    verify_value("FROM_ENV_MISSING", "missing")
+
+    verify_value("FROM_ENV_WEIRD", "weird")
+
+
     print("Testing defined vs undefined symbols")
 
     for name in "A", "B", "C", "D", "BOOL", "TRISTATE", "STRING", "INT", "HEX":