Detect iconv type at compile time instead of project generation

Author: wangqr

CMakeLists.txt

@@ -520,12 +520,8 @@ target_include_directories(Aegisub PRIVATE ${OPENGL_INCLUDE_DIR})
 target_link_libraries(Aegisub ${OPENGL_LIBRARIES})
 
 find_package(Iconv REQUIRED)
-target_compile_definitions(libaegisub PRIVATE "HAVE_ICONV")
 target_include_directories(libaegisub PRIVATE ${Iconv_INCLUDE_DIRS})
 target_link_libraries(libaegisub ${Iconv_LIBRARIES})
-if(NOT Iconv_IS_BUILT_IN)
-    target_compile_definitions(libaegisub PRIVATE "AGI_ICONV_CONST")
-endif()
 
 find_package(ICU REQUIRED uc dt in)
 target_include_directories(libaegisub PRIVATE ${ICU_INCLUDE_DIRS})

configure.ac

@@ -272,20 +272,6 @@ AC_SUBST(ICONV_CFLAGS)
 
 AS_IF([test x$agi_cv_with_iconv = xno], [AC_MSG_FAILURE([Please install a working iconv library.])])
 
-AC_AGI_COMPILE([iconv (const)], [iconv_const], [$ICONV_CFLAGS], [$ICONV_LIBS],[
-#include <iconv.h>
-int main(void) {
-  iconv_t cd = iconv_open("UTF-16", "UTF-8");
-  const char *in = "in";
-  char *out = new char();
-  size_t res, inbytesleft, outbytesleft;
-  res = iconv(cd, &in, &inbytesleft, &out, &outbytesleft);
-  return 0;
-} ])
-
-AS_IF([test x$agi_cv_with_iconv_const = xyes],
-      [AC_DEFINE(AGI_ICONV_CONST, 1, [Enable if iconv expects the in argument to be const])])
-
 ###############
 # Audio Players
 ###############

libaegisub/common/charset_conv.cpp

@@ -33,12 +33,6 @@
 #define ICONV_POSIX
 #endif
 
-#ifdef AGI_ICONV_CONST
-#define ICONV_CONST_CAST(a) a
-#else
-#define ICONV_CONST_CAST(a) const_cast<char **>(a)
-#endif
-
 static const iconv_t iconv_invalid = (iconv_t)-1;
 static const size_t iconv_failed = (size_t)-1;
 
@@ -286,7 +280,13 @@ Iconv::~Iconv() {
 }
 
 size_t Iconv::operator()(const char **inbuf, size_t *inbytesleft, char **outbuf, size_t *outbytesleft) {
-	return iconv(cd, ICONV_CONST_CAST(inbuf), inbytesleft, outbuf, outbytesleft);
+	struct InbufConstCast{
+		const char** p;
+		InbufConstCast(const char** p) : p(p) {}
+		operator const char** () const { return p; }
+		operator char** () const { return const_cast<char**>(p); }
+	} inbuf_const_cast(inbuf);
+	return iconv(cd, inbuf_const_cast, inbytesleft, outbuf, outbytesleft);
 }
 
 IconvWrapper::IconvWrapper(const char* sourceEncoding, const char* destEncoding, bool enableSubst)