phase3: nullfix field-formal field-nullable handler. 907 -> 872

tools/nullfix.py

@@ -101,6 +101,17 @@ def insert_bang(line, col0, name, kind):
         return None
     return None
 
+def make_field_nullable(lines, name):
+    """找字段声明 'Type name;' 并在类型后加 '?'。返回 (行索引, 新行) 或 (None,None)。"""
+    pat = re.compile(r'^(\s+(?:final\s+|const\s+)?(?:static\s+)?)(.+)\s+'+re.escape(name)+r';\s*$')
+    for i,L in enumerate(lines):
+        m=pat.match(L)
+        if not m: continue
+        mod, typ = m.group(1), m.group(2).rstrip()
+        if '?' in typ or '=' in L: continue
+        return i, f"{mod}{typ}? {name};"
+    return None, None
+
 def insert_late(line):
     stripped=line.strip()
     if not stripped or stripped.startswith('late '): return None
@@ -147,7 +158,16 @@ def apply_round(errs):
             if cls: new=insert_bang(old, col-1, cls[0], cls[1])
         elif rule=='missing_default_value_for_parameter':
             nm=NAME.search(msg)
-            if nm: new=insert_nullable_before_name(old, nm.group(1), col-1)
+            if nm:
+                pname=nm.group(1)
+                # field-formal this.x ? 则把字段改可空（跨行）
+                if ('this.'+pname) in old:
+                    fl=get(path)
+                    fi, fnew = make_field_nullable(fl, pname)
+                    if fi is not None and fl[fi]!=fnew:
+                        fl[fi]=fnew; changed+=1
+                else:
+                    new=insert_nullable_before_name(old, pname, col-1)
         elif rule in ('not_initialized_non_nullable_instance_field','not_initialized_non_nullable_variable'):
             new=insert_late(old)
         if new and new!=old: