Fix warning for when 2nd `iconv()` argument is const

CMakeLists.txt

@@ -514,6 +514,9 @@ endforeach()
 
 if(ICONV_FOUND)
     add_definitions(-DHAVE_ICONV)
+    if(ICONV_SECOND_ARGUMENT_IS_CONST)
+        add_definitions(-DICONV_SECOND_ARGUMENT_IS_CONST)
+    endif()
 endif()
 
 # if(MINGW)

cmake/FindICONV.cmake

@@ -22,8 +22,7 @@ if(ICONV_FOUND AND NOT DEFINED ICONV_SECOND_ARGUMENT_IS_CONST)
     set(CMAKE_REQUIRED_INCLUDES ${ICONV_INCLUDE_DIRS})
     set(CMAKE_REQUIRED_LIBRARIES ${ICONV_LIBRARIES})
 
-    check_c_source_compiles(
-        "
+    check_c_source_compiles("
         #include <iconv.h>
         int main ()
         {
@@ -34,7 +33,10 @@ if(ICONV_FOUND AND NOT DEFINED ICONV_SECOND_ARGUMENT_IS_CONST)
             size_t olen = 0;
             iconv (conv, &in, &ilen, &out, &olen);
             return 0;
-        }" ICONV_SECOND_ARGUMENT_IS_CONST)
+        }"
+        ICONV_SECOND_ARGUMENT_IS_CONST
+        FAIL_REGEX "incompatible pointer type"
+        FAIL_REGEX "discards qualifiers in nested pointer types")
 
     set(CMAKE_REQUIRED_INCLUDES)
     set(CMAKE_REQUIRED_LIBRARIES)

libtransmission/utils.c

@@ -1034,7 +1034,11 @@ to_utf8 (const char * in, size_t inlen)
 
   for (i=0; !ret && i<encoding_count; ++i)
     {
+#ifdef ICONV_SECOND_ARGUMENT_IS_CONST
+      const char * inbuf = in;
+#else
       char * inbuf = (char*) in;
+#endif
       char * outbuf = out;
       size_t inbytesleft = inlen;
       size_t outbytesleft = buflen;