[clang] [Clang] Use const pointer to eliminate warning with libxml 2.12.0 (PR #76719)

[via cfe-commits]

https://github.com/FantasqueX created https://github.com/llvm/llvm-project/pull/76719

Currently, if `CLANG_HAVE_LIBXML` is defined, and the version of libxml2 is above 2.12.0, there will be two warnings when building clang.

warning: initializing 'xmlErrorPtr' (aka 'struct _xmlError *') with an expression of type 'const xmlError *' (aka 'const struct _xmlError *') discards qualifiers

Since this commit
https://gitlab.gnome.org/GNOME/libxml2/-/commit/45470611b047db78106dcb2fdbd4164163c15ab7, libxml2 makes cmlGetLastError return a const error. This patch follows libxml2. Making the result a const pointer should be compatible with versions before 2.12.0.

Tested on ArchLinux with libxml2 2.12.3 installed.

>From 603f9c000f4bdecb20449b22c55d6c2eda88f134 Mon Sep 17 00:00:00 2001
From: Letu Ren <fantasquex at gmail.com>
Date: Tue, 2 Jan 2024 21:50:45 +0800
Subject: [PATCH] [Clang] Use const pointer to eliminate warning with libxml
 2.12.0

Currently, if `CLANG_HAVE_LIBXML` is defined, and the version of libxml2
is above 2.12.0, there will be two warnings when building clang.

warning: initializing 'xmlErrorPtr' (aka 'struct _xmlError *') with an
expression of type 'const xmlError *' (aka 'const struct _xmlError *')
discards qualifiers

Since this commit
https://gitlab.gnome.org/GNOME/libxml2/-/commit/45470611b047db78106dcb2fdbd4164163c15ab7,
libxml2 makes cmlGetLastError return a const error. This patch follows
libxml2. Making the result a const pointer should be compatible with
versions before 2.12.0.

Tested on ArchLinux with libxml2 2.12.3 installed.
---
 clang/tools/c-index-test/c-index-test.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/tools/c-index-test/c-index-test.c b/clang/tools/c-index-test/c-index-test.c
index 6fa400a0675b7a..a79da8eac30972 100644
--- a/clang/tools/c-index-test/c-index-test.c
+++ b/clang/tools/c-index-test/c-index-test.c
@@ -695,7 +695,7 @@ static void ValidateCommentXML(const char *Str, const char *CommentSchemaFile) {
   Doc = xmlParseDoc((const xmlChar *) Str);
 
   if (!Doc) {
-    xmlErrorPtr Error = xmlGetLastError();
+    const xmlError *Error = xmlGetLastError();
     printf(" CommentXMLInvalid [not well-formed XML: %s]", Error->message);
     return;
   }
@@ -705,7 +705,7 @@ static void ValidateCommentXML(const char *Str, const char *CommentSchemaFile) {
   if (!status)
     printf(" CommentXMLValid");
   else if (status > 0) {
-    xmlErrorPtr Error = xmlGetLastError();
+    const xmlError *Error = xmlGetLastError();
     printf(" CommentXMLInvalid [not valid XML: %s]", Error->message);
   } else
     printf(" libXMLError");