Reduce cap length of cnames generated from long function argument lis…

…ts (GH-6104)

Because max_prefix was much less than max_len, it was actually just making the names longer.

Closes #6052

Cython/Compiler/PyrexTypes.py

@@ -3490,8 +3490,12 @@ def create_to_py_utility_code(self, env):
         def arg_name_part(arg):
             return "%s%s" % (len(arg.name), punycodify_name(arg.name)) if arg.name else "0"
         arg_names = [ arg_name_part(arg) for arg in self.args ]
-        arg_names = "_".join(arg_names)
+        arg_names = cap_length("_".join(arg_names))
         safe_typename = type_identifier(self, pyrex=True)
+        # Note that the length here is slightly bigger than twice the default cap in
+        # "cap_length" (since the length is capped in both arg_names and the type_identifier)
+        # but since this is significantly shorter than compilers should be able to handle,
+        # that is acceptable.
         to_py_function = "__Pyx_CFunc_%s_to_py_%s" % (safe_typename, arg_names)
 
         for arg in self.args:
@@ -5486,8 +5490,8 @@ def type_identifier_from_declaration(decl, scope = None):
         _type_identifier_cache[key] = safe
     return safe
 
-def cap_length(s, max_prefix=63, max_len=1024):
-    if len(s) <= max_prefix:
+def cap_length(s, max_len=63):
+    if len(s) <= max_len:
         return s
     hash_prefix = hashlib.sha256(s.encode('ascii')).hexdigest()[:6]
     return '%s__%s__etc' % (hash_prefix, s[:max_len-17])

Cython/Compiler/Tests/TestTypes.py

@@ -59,9 +59,9 @@ def test_type_identifier_for_declaration(self):
             ("const &&&std::vector", "const__fwref__refstd__in_vector"),
             ("const &&std::vector", "const__fwrefstd__in_vector"),
             ("void (*func)(int x, float y)",
-             "975d51__void__lParen__ptrfunc__rParen__lParenint__space_x__comma_float__space_y__rParen__etc"),
+             "975d51__void__lParen__ptrfunc__rParen__lParenint__spac__etc"),
             ("float ** (*func)(int x, int[:] y)",
-             "31883a__float__ptr__ptr__lParen__ptrfunc__rParen__lParenint__space_x__comma_int__lArr__D__rArry__rParen__etc"),
+             "31883a__float__ptr__ptr__lParen__ptrfunc__rParen__lPar__etc"),
         ]
         self._test_escape(function_name, test_data)
 
@@ -71,3 +71,5 @@ def _test_escape(self, func_name, test_data=TEST_DATA):
             escaped_value = escape(declaration)
             self.assertEqual(escaped_value, expected, "%s('%s') == '%s' != '%s'" % (
                 func_name, declaration, escaped_value, expected))
+            # test that the length has been successfully capped
+            self.assertLessEqual(len(escaped_value), 64)