From dce47d5020064fb1fc0c58db165d72c7ffd10835 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Sun, 20 Oct 2019 19:24:37 +0100
Subject: [PATCH] pyke/pyke.c: Check conversions hidden inside `KWLIST' and
 `KWMETH'.

Introduce a new macro `CONVERT_CAREFULLY' which checks (via a rather
sleazy hack) that its operand is of the expected type before converting
it to some other type.  This is protected by an `#ifdef' guard because
I'm thinking about adding it to a version of mLib, but I want to keep
the Pyke core independent of mLib.

Use this new macro to build better versions of `KWLIST' and `KWMETH',
which have casts hidden inside them, so that we can now be certain that
the method table entries match up with the functions.  (Spoiler: they
didn't, quite, and commit 19bff42f99d41cd9b8953ff61edfe35380b54d88,
backported onto the 1.1.x branch, fixes the bug that was found by this
change.)
---
 pyke.h | 43 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/pyke.h b/pyke.h
index 4e67464..b91b48d 100644
--- a/pyke.h
+++ b/pyke.h
@@ -160,7 +160,24 @@ extern PyObject *getulong(unsigned long); /* any kind of unsigned integer */
 extern PyObject *abstract_pynew(PyTypeObject *, PyObject *, PyObject *);
   /* A `tp_new' function which refuses to make the object. */
 
-#define KWLIST (/*unconst*/ char **)kwlist
+#ifndef CONVERT_CAREFULLY
+#  define CONVERT_CAREFULLY(newty, expty, obj)				\
+     (!sizeof(*(expty *)0 = (obj)) + (/*unconst*/ newty)(obj))
+  /* Convert OBJ to the type NEWTY, having previously checked that it is
+   * convertible to the expected type EXPTY.
+   *
+   * Because of the way we set up types, we can make many kinds of tables be
+   * `const' which can't usually be so (because Python will want to fiddle
+   * with their reference counts); and, besides, Python's internals are
+   * generally quite bad at being `const'-correct about tables.  One frequent
+   * application of this macro, then, is in removing `const' from a type
+   * without sacrificing all type safety.  The other common use is in
+   * checking that method function types match up with the signatures
+   * expected in their method definitions.
+   */
+#endif
+
+#define KWLIST CONVERT_CAREFULLY(char **, const char *const *, kwlist)
   /* Strip `const' qualifiers from the keyword list `kwlist'.  Useful when
    * calling `PyArg_ParseTupleAndKeywords', which isn't `const'-correct.
    */
@@ -209,6 +226,17 @@ extern PyTypeObject *inittype(PyTypeObject */*skel*/,
 #define INITTYPE(ty, base) INITTYPE_META(ty, base, type)
   /* Macros to initialize a type from its skeleton. */
 
+/* Macros for filling in `PyMethodDef' tables, ensuring that functions have
+ * the expected signatures.
+ */
+#define STD_METHOD(decor, func, doc)					\
+  { #func, decor(func), METH_VARARGS, doc },
+#define KEYWORD_METHOD(decor, func, doc)				\
+  { #func,								\
+    CONVERT_CAREFULLY(PyCFunction, PyCFunctionWithKeywords, decor(func)), \
+    METH_VARARGS | METH_KEYWORDS,					\
+    doc },
+
 /* Convenience wrappers for filling in `PyMethodDef' tables, following
  * Pyke naming convention.  Define `METHNAME' locally as
  *
@@ -216,11 +244,8 @@ extern PyTypeObject *inittype(PyTypeObject */*skel*/,
  *
  * around the method table.
  */
-#define METH(func, doc)							\
-  { #func, METHNAME(func), METH_VARARGS, doc },
-#define KWMETH(func, doc)						\
-  { #func, (PyCFunction)METHNAME(func),					\
-    METH_VARARGS | METH_KEYWORDS, doc },
+#define METH(func, doc) STD_METHOD(METHNAME, func, doc)
+#define KWMETH(func, doc) KEYWORD_METHOD(METHNAME, func, doc)
 
 /* Convenience wrappers for filling in `PyGetSetDef' tables, following Pyke
  * naming convention.  Define `GETSETNAME' locally as
@@ -319,9 +344,9 @@ extern PyMethodDef *donemethods(void);
 /*----- Generic mapping support -------------------------------------------*/
 
 /* Mapping methods. */
-#define GMAP_METH(func, doc) { #func, gmapmeth_##func, METH_VARARGS, doc },
-#define GMAP_KWMETH(func, doc)						\
-  { #func, (PyCFunction)gmapmeth_##func, METH_VARARGS|METH_KEYWORDS, doc },
+#define GMAP_METMNAME(func) gmapmeth_##func
+#define GMAP_METH(func, doc) STD_METHOD(GMAP_METMNAME, func, doc)
+#define GMAP_KWMETH(func, doc) KEYWORD_METHOD(GMAP_METMNAME, func, doc)
 #define GMAP_METHDECL(func, doc)					\
   extern PyObject *gmapmeth_##func(PyObject *, PyObject *);
 #define GMAP_KWMETHDECL(func, doc)					\
-- 
2.11.0