pythongh-128152: Argument Clinic: ignore pre-processor directives inside C comments (python#128464)

Author: erlend-aasland

Lib/test/test_clinic.py

@@ -740,6 +740,16 @@ def test_cloned_forced_text_signature_illegal(self):
         err = "Cannot use @text_signature when cloning a function"
         self.expect_failure(block, err, lineno=11)
 
+    def test_ignore_preprocessor_in_comments(self):
+        for dsl in "clinic", "python":
+            raw = dedent(f"""\
+                /*[{dsl} input]
+                # CPP directives, valid or not, should be ignored in C comments.
+                #
+                [{dsl} start generated code]*/
+            """)
+            self.clinic.parse(raw)
+
 
 class ParseFileUnitTest(TestCase):
     def expect_parsing_failure(

Misc/NEWS.d/next/Tools-Demos/2025-01-03-23-51-07.gh-issue-128152.IhzElS.rst

@@ -0,0 +1,2 @@
+Fix a bug where Argument Clinic's C pre-processor parser tried to parse
+pre-processor directives inside C comments. Patch by Erlend Aasland.

Tools/clinic/libclinic/cpp.py

@@ -132,6 +132,9 @@ def pop_stack() -> TokenAndCondition:
         if line_comment:
             line = before.rstrip()
 
+        if self.in_comment:
+            return
+
         if not line.startswith('#'):
             return