Compilation fails with GCC 16: discarded-qualifiers

[xfgusta]

trurl 0.16.1 fails to build from source with GCC 16 in Fedora rawhide/f44:

Details

trurl.c: In function ‘encodeassign’:
trurl.c:486:13: error: initialization discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
  486 |   char *p = strchr(query, '=');
      |             ^~~~~~
trurl.c: In function ‘getarg’:
trurl.c:603:20: error: initialization discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
  603 |     char *equals = strchr(&flag[2], '=');
      |                    ^~~~~~
trurl.c: In function ‘get’:
trurl.c:872:13: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
  872 |         end = strchr(ptr, endbyte);
      |             ^
trurl.c:888:14: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
  888 |           cl = memchr(ptr, ':', vlen);
      |              ^
trurl.c: In function ‘setone’:
trurl.c:1025:15: error: initialization discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 1025 |   char *ptr = strchr(setline, '=');
      |               ^~~~~~
trurl.c: In function ‘canonical_path’:
trurl.c:1695:8: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 1695 |     sl = memchr(path, '/', len);
      |        ^
trurl.c: In function ‘singleurl’:
trurl.c:1819:13: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 1819 |         sep = strchr(part, '=');
      |             ^
trurl.c:1855:11: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 1855 |       sep = strchr(w, ' ');
      |           ^

Applying the following patch fixes these errors in trurl 0.16.1:

Details

diff --git a/trurl.c b/trurl.c
index b5a716c..8ff2112 100644
--- a/trurl.c
+++ b/trurl.c
@@ -483,7 +483,7 @@ static void pathadd(struct option *o, const char *path)
 
 static char *encodeassign(const char *query)
 {
-  char *p = strchr(query, '=');
+  const char *p = strchr(query, '=');
   char *urle;
   if(p) {
     /* URL encode the left and the right side of the '=' separately */
@@ -600,9 +600,9 @@ static int getarg(struct option *o,
     gap = false;
   }
   else if((flag[0] == '-') && (flag[1] == '-')) {
-    char *equals = strchr(&flag[2], '=');
+    const char *equals = strchr(&flag[2], '=');
     if(equals) {
-      arg = (char *)&equals[1];
+      arg = &equals[1];
       gap = false;
     }
   }
@@ -862,14 +862,14 @@ static void get(struct option *o, CURLU *uh)
         /* this is meant as a variable to output */
         const char *start = ptr;
         char *end;
-        char *cl;
+        const char *cl;
         size_t vlen;
         bool isquery = false;
         bool queryall = false;
         bool strict = false; /* strict mode, fail on URL decode problems */
         bool must = false; /* must mode, fail on missing component */
         int mods = 0;
-        end = strchr(ptr, endbyte);
+        end = (char *)strchr(ptr, endbyte);
         ptr++; /* pass the { */
         if(!end) {
           /* syntax error */
@@ -1022,7 +1022,7 @@ static void get(struct option *o, CURLU *uh)
 static const struct var *setone(CURLU *uh, const char *setline,
                                 struct option *o)
 {
-  char *ptr = strchr(setline, '=');
+  const char *ptr = strchr(setline, '=');
   const struct var *v = NULL;
   if(ptr && (ptr > setline)) {
     size_t vlen = ptr - setline;
@@ -1684,7 +1684,7 @@ static char *canonical_path(const char *path)
 {
   /* split the path per slash, URL decode + encode, then put together again */
   size_t len = strlen(path);
-  char *sl;
+  const char *sl;
   char *dupe = NULL;
 
   do {
@@ -1810,7 +1810,7 @@ static void singleurl(struct option *o,
       size_t plen;
       const char *w;
       size_t wlen;
-      char *sep;
+      const char *sep;
       bool urlencode = true;
       const struct var *v;
 
@@ -1855,7 +1855,7 @@ static void singleurl(struct option *o,
       sep = strchr(w, ' ');
       if(sep) {
         wlen = sep - w;
-        iinfo->ptr = sep + 1; /* next word is here */
+        iinfo->ptr = (char *)(sep + 1); /* next word is here */
       }
       else {
         /* last word */

https://fedoraproject.org/wiki/Fedora_44_GCC_16_mass_prebuild#Discarding_const_qualifiers_of_input_arguments_to_string_functions

[vszakats]

Thanks @xfgusta, this should be fixed via #432.

[vpzomtrrfrt]

I still see this issue, both in 6e1479c and current master:

cc $(curl-config --cflags) -W -Wall -pedantic -Wconversion -Wmissing-prototypes -Wshadow -Wsign-compare -Wno-sign-conversion -Wwrite-strings -Wcast-qual -Wdeclaration-after-statement -Wmissing-noreturn -Werror -g   -c -o trurl.o trurl.c
trurl.c: In function ‘singleurl’:
trurl.c:1869:12: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 1869 |       sepw = strchr(w, ' ');
      |            ^
cc1: all warnings being treated as errors
make: *** [<builtin>: trurl.o] Error 1

[vszakats]

@vpzomtrrfrt Thanks, should be fixed after b3c2faf #447.
Also CI-tested now via 84b21f0 #446.