Add check for ignored configs & exit on error

- Add warning for a config you try to set but cannot due to
dependencies.
- Make message prefix conditional on if warnings are treated as errors
or not
- Exit with error if `warn_to_stderr` enabled

Author: STABL-SW

kconfiglib.py

@@ -1353,6 +1353,12 @@ def _load_config(self, filename, replace):
 
                 sym.set_value(val)
 
+                if val != sym.str_value:
+                    self._warn("{} was assigned the value '{}', but got the "
+                             "value '{}'. Check the symbol's dependencies, and make "
+                             "sure that it has a prompt."
+                             .format(name, val, sym.str_value))
+
         if replace:
             # If we're replacing the configuration, unset the symbols that
             # didn't get set
@@ -3995,13 +4001,15 @@ def _warn(self, msg, filename=None, linenr=None):
         if not self.warn:
             return
 
-        msg = "warning: " + msg
+        prefix = "error: " if self.warn_to_stderr else "warning: "
+        msg = prefix + msg
         if filename is not None:
             msg = "{}:{}: {}".format(filename, linenr, msg)
 
         self.warnings.append(msg)
         if self.warn_to_stderr:
             sys.stderr.write(msg + "\n")
+            sys.exit(1)
 
 
 class Symbol(object):
@@ -4892,6 +4900,8 @@ def _rec_invalidate(self):
             # Invalidating MODULES has wide-ranging effects
             self.kconfig._invalidate_all()
         else:
+            # print(self)
+            # print("invalidated")
             self._invalidate()
 
             for item in self._dependents: