pythongh-64595: Fix write file logic in Argument Clinic

Check if any clinic output actually changes any of the output files
before deciding if we should touch the source file. This needs to be
done before we eventually update the source file.

Author: erlend-aasland

Diff for: Tools/clinic/clinic.py

@@ -1965,16 +1965,20 @@ def dump(self):
 return_converters = {}
 
 
-def write_file(filename, new_contents, force=False):
+def file_changed(filename: str, new_contents: str) -> bool:
+    """Return true if file contents changed (meaning we must update it)"""
     try:
         with open(filename, 'r', encoding="utf-8") as fp:
             old_contents = fp.read()
-
-        if old_contents == new_contents and not force:
-            # no change: avoid modifying the file modification time
-            return
+        return old_contents != new_contents
     except FileNotFoundError:
-        pass
+        return True
+
+
+def write_file(filename: str, new_contents: str, force=False):
+    if not force and not file_changed(filename, new_contents):
+        # no change: avoid modifying the file modification time
+        return
 
     # Atomic write using a temporary file and os.replace()
     filename_new = f"{filename}.new"
@@ -2238,7 +2242,7 @@ def parse_file(filename, *, verify=True, output=None):
     src_out, clinic_out = clinic.parse(raw)
 
     # If clinic output changed, force updating the source file as well.
-    force = bool(clinic_out)
+    force = any(file_changed(fn, data) for fn, data in clinic_out)
     write_file(output, src_out, force=force)
     for fn, data in clinic_out:
         write_file(fn, data)