fix(build): glibc 2.43 happened

using the GNU compiler we just get a bunch of const warnings we can fix.
clang, however, gets really upset that the standard library suddenly
starts using a lot of c11 features, despite us being in -std=gnu99 mode.

Basically, _GNU_SOURCE which we set is taken as a _carte blanche_ by the
glibc headers to do whatever they please, and thus we must inform clang
that everything is still OK.

src/nvim/CMakeLists.txt

@@ -137,7 +137,8 @@ elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU")
 elseif(CMAKE_C_COMPILER_ID MATCHES "Clang")
   # On FreeBSD 64 math.h uses unguarded C11 extension, which taints clang
   # 3.4.1 used there.
-  if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
+  # on GNU/Linux, glibc 2.43 is tainted with c11 features when you use _GNU_SOURCE
+  if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD" OR CMAKE_SYSTEM_NAME STREQUAL "Linux")
     target_compile_options(main_lib INTERFACE -Wno-c11-extensions)
   endif()
 
@@ -1029,4 +1030,4 @@ add_target(lintdocurls
   COMMAND ${NVIM_LUA} scripts/lintdoc.lua true
   DEPENDS ${DOCFILES}
   CUSTOM_COMMAND_ARGS USES_TERMINAL)
-add_dependencies(lintdocurls nvim)
+add_dependencies(lintdocurls nvim)

src/nvim/api/private/validate.c

@@ -14,7 +14,7 @@ void api_err_invalid(Error *err, const char *name, const char *val_s, int64_t va
   ErrorType errtype = kErrorTypeValidation;
   // Treat `name` without whitespace as a parameter (surround in quotes).
   // Treat `name` with whitespace as a description (no quotes).
-  char *has_space = strchr(name, ' ');
+  const char *has_space = strchr(name, ' ');
 
   // No value.
   if (val_s && val_s[0] == NUL) {
@@ -43,7 +43,7 @@ void api_err_exp(Error *err, const char *name, const char *expected, const char
   ErrorType errtype = kErrorTypeValidation;
   // Treat `name` without whitespace as a parameter (surround in quotes).
   // Treat `name` with whitespace as a description (no quotes).
-  char *has_space = strchr(name, ' ');
+  const char *has_space = strchr(name, ' ');
 
   if (!actual) {
     api_set_error(err, errtype,

src/nvim/cmdexpand.c

@@ -1783,7 +1783,8 @@ static const char *find_cmd_after_isearch_cmd(expand_T *xp, const char *arg)
 /// Set the completion context for the :unlet command. Always returns NULL.
 static const char *set_context_in_unlet_cmd(expand_T *xp, const char *arg)
 {
-  while ((xp->xp_pattern = strchr(arg, ' ')) != NULL) {
+  // NOLINTNEXTLINE(*-casting): remove once CI uses glibc 2.43
+  while ((xp->xp_pattern = (char *)strchr(arg, ' ')) != NULL) {
     arg = xp->xp_pattern + 1;
   }
 
@@ -2165,7 +2166,8 @@ static const char *set_context_by_cmdname(const char *cmd, cmdidx_T cmdidx, expa
   case CMD_bdelete:
   case CMD_bwipeout:
   case CMD_bunload:
-    while ((xp->xp_pattern = strchr(arg, ' ')) != NULL) {
+    // NOLINTNEXTLINE(*-casting): remove once CI uses glibc 2.43
+    while ((xp->xp_pattern = (char *)strchr(arg, ' ')) != NULL) {
       arg = xp->xp_pattern + 1;
     }
     FALLTHROUGH;

src/nvim/event/socket.c

@@ -27,7 +27,7 @@
 ///
 /// @param address Address string
 /// @return pointer to the end of the host part of the address, or NULL if it is not a TCP address
-char *socket_address_tcp_host_end(const char *address)
+char *socket_address_tcp_host_end(char *address)
 {
   if (address == NULL) {
     return NULL;

src/nvim/lua/stdlib.c

@@ -474,8 +474,8 @@ static int nlua_stricmp(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
   size_t s2_len;
   const char *s1 = luaL_checklstring(lstate, 1, &s1_len);
   const char *s2 = luaL_checklstring(lstate, 2, &s2_len);
-  char *nul1;
-  char *nul2;
+  const char *nul1;
+  const char *nul2;
   int ret = 0;
   assert(s1[s1_len] == NUL);
   assert(s2[s2_len] == NUL);

src/nvim/strings.c

@@ -509,12 +509,14 @@ char *vim_strchr(const char *const string, const int c)
   if (c <= 0) {
     return NULL;
   } else if (c < 0x80) {
-    return strchr(string, c);
+    // NOLINTNEXTLINE(*-casting): remove once CI uses glibc 2.43
+    return (char *)strchr(string, c);
   } else {
     char u8char[MB_MAXBYTES + 1];
     const int len = utf_char2bytes(c, u8char);
     u8char[len] = NUL;
-    return strstr(string, u8char);
+    // NOLINTNEXTLINE(*-casting): remove once CI uses glibc 2.43
+    return (char *)strstr(string, u8char);
   }
 }