[Python-checkins] Fix compiler warning in the xml module (GH-26245) (GH-26249)

[pablogsal]

https://github.com/python/cpython/commit/e87fd41d02ab6dff9cee4f024e4e8c3c179fe255
commit: e87fd41d02ab6dff9cee4f024e4e8c3c179fe255
branch: 3.10
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: pablogsal <Pablogsal at gmail.com>
date: 2021-05-19T19:21:19+01:00
summary:

Fix compiler warning in the xml module (GH-26245) (GH-26249)

The newest version of gcc complains about passing un-initialized arrays
as constant pointers:

```
/Modules/expat/xmltok_ns.c: In function ‘findEncodingNS’:
/Modules/expat/xmltok.h:272:10: warning: ‘buf’ may be used uninitialized [-Wmaybe-uninitialized]
  272 |   (((enc)->utf8Convert)(enc, fromP, fromLim, toP, toLim))
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Modules/expat/xmltok_ns.c:95:3: note: in expansion of macro ‘XmlUtf8Convert’
   95 |   XmlUtf8Convert(enc, &ptr, end, &p, p + ENCODING_MAX - 1);
      |   ^~~~~~~~~~~~~~
/Modules/expat/xmltok.h:272:10: note: by argument 5 of type ‘const char *’ to ‘enum XML_Convert_Result(const ENCODING *, const char **, const char *, char **, const char *)’ {aka ‘enum XML_Convert_Result(const struct encoding *, const char **, const char *, char **, const char *)’}
  272 |   (((enc)->utf8Convert)(enc, fromP, fromLim, toP, toLim))
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Modules/expat/xmltok_ns.c:95:3: note: in expansion of macro ‘XmlUtf8Convert’
   95 |   XmlUtf8Convert(enc, &ptr, end, &p, p + ENCODING_MAX - 1);
      |   ^~~~~~~~~~~~~~
In file included from /Modules/expat/xmltok.c:1657:
/Modules/expat/xmltok_ns.c:92:8: note: ‘buf’ declared here
   92 |   char buf[ENCODING_MAX];

```
(cherry picked from commit be93f81e58ba3742589259ef84325a95b547e424)

Co-authored-by: Pablo Galindo <Pablogsal at gmail.com>

Co-authored-by: Pablo Galindo <Pablogsal at gmail.com>

files:
M Modules/expat/xmltok_ns.c

diff --git a/Modules/expat/xmltok_ns.c b/Modules/expat/xmltok_ns.c
index 919c74e9f97fe..e1b46a7c04c4e 100644
--- a/Modules/expat/xmltok_ns.c
+++ b/Modules/expat/xmltok_ns.c
@@ -89,7 +89,7 @@ NS(XmlInitEncoding)(INIT_ENCODING *p, const ENCODING **encPtr,
 static const ENCODING *
 NS(findEncoding)(const ENCODING *enc, const char *ptr, const char *end) {
 #  define ENCODING_MAX 128
-  char buf[ENCODING_MAX];
+  char buf[ENCODING_MAX] = {0};
   char *p = buf;
   int i;
   XmlUtf8Convert(enc, &ptr, end, &p, p + ENCODING_MAX - 1);