gen_invocations: handle undefined values

When evaluating XML condition expressions, properly treat undefined
values as undefined, not as False. Otherwise, the negation of an
undefined value may make an entire expression true and incorrectly
label some methods as MCS methods.

Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

manual/tools/gen_invocations.py

@@ -65,6 +65,7 @@ def eval_condition(condition, values):
     """
 
     pos = 0
+    undefined = "Undef"
 
     def accept(string):
         nonlocal pos
@@ -94,7 +95,7 @@ def eval_condition(condition, values):
         end = pos
         if not accept(")"):
             return None
-        return values.get(condition[start:end], "False")
+        return values.get(condition[start:end], undefined)
 
     def parse_not():
         nonlocal pos
@@ -106,6 +107,8 @@ def eval_condition(condition, values):
             return "False"
         elif term == "False":
             return "True"
+        elif term == undefined:
+            return undefined
         else:
             return None
 
@@ -143,11 +146,13 @@ def eval_condition(condition, values):
     cond = parse_condition()
     skip_whitespace()
     if not cond or pos != len(condition):
-        raise Exception(f"Failed to parse condition '{condition}'")
+        raise Exception(f"Failed to parse condition '{condition}' (got {cond} at {pos})")
     if cond == "True":
         return True
     if cond == "False":
         return False
+    if cond == undefined:
+        return None
     raise Exception(f"Unexpected value {cond} for condition '{condition}'")
 
 
@@ -155,7 +160,7 @@ def is_mcs(method_condition):
     """
     Returns whether the condition evaluates to true when CONFIG_KERNEL_MCS is set.
     """
-    return eval_condition(method_condition, {"CONFIG_KERNEL_MCS": "True"})
+    return eval_condition(method_condition, {"CONFIG_KERNEL_MCS": "True"}) is True
 
 
 def gen_invocations(input_files, output_dir, args):