Auto-detect C++ extensions needed to build

ext/charlock_holmes/common.h

@@ -38,4 +38,19 @@ static inline VALUE charlock_new_str2(const char *str)
 #endif
 }
 
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+extern void Init_charlock_holmes();
+extern void _init_charlock_encoding_detector();
+extern void _init_charlock_converter();
+extern void _init_charlock_transliterator();
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif

ext/charlock_holmes/converter.c

@@ -29,7 +29,7 @@ static VALUE rb_converter_convert(VALUE self, VALUE rb_txt, VALUE rb_src_enc, VA
 	if (status != U_BUFFER_OVERFLOW_ERROR) {
 		rb_raise(rb_eArgError, "%s", u_errorName(status));
 	}
-	out_buf = malloc(out_len);
+	out_buf = (char *) malloc(out_len);
 
 	// now do the actual conversion
 	status = U_ZERO_ERROR;

ext/charlock_holmes/encoding_detector.c

@@ -352,7 +352,7 @@ static VALUE rb_encdec__alloc(VALUE klass)
 	UErrorCode status = U_ZERO_ERROR;
 	VALUE obj;
 
-	detector = calloc(1, sizeof(charlock_detector_t));
+	detector = (charlock_detector_t *) calloc(1, sizeof(charlock_detector_t));
 	obj = Data_Wrap_Struct(klass, NULL, rb_encdec__free, (void *)detector);
 
 	detector->csd = ucsdet_open(&status);

ext/charlock_holmes/ext.c

@@ -1,9 +1,5 @@
 #include "common.h"
 
-extern void _init_charlock_encoding_detector();
-extern void _init_charlock_converter();
-extern void _init_charlock_transliterator();
-
 VALUE rb_mCharlockHolmes;
 
 void Init_charlock_holmes() {
@@ -12,4 +8,4 @@ void Init_charlock_holmes() {
 	_init_charlock_encoding_detector();
 	_init_charlock_converter();
 	_init_charlock_transliterator();
-}
+}

ext/charlock_holmes/extconf.rb

@@ -49,4 +49,30 @@
 $CFLAGS << ' -Wall -funroll-loops'
 $CFLAGS << ' -Wextra -O0 -ggdb3' if ENV['DEBUG']
 
+minimal_program = <<~SRC
+  #include <unicode/translit.h>
+  int main() { return 0; }
+SRC
+
+# Pass -x c++ to force gcc to compile the test program
+# as C++ (as it will end in .c by default).
+compile_options = +"-x c++"
+
+icu_requires_version_flag = checking_for("icu that requires explicit C++ version flag") do
+  !try_compile(minimal_program, compile_options)
+end
+
+if icu_requires_version_flag
+  abort "Cannot compile icu with your compiler: recent versions require C++17 support." unless %w[c++20 c++17 c++11 c++0x].any? do |std|
+    checking_for("icu that compiles with #{std} standard") do
+      flags = compile_options + " -std=#{std}"
+      if try_compile(minimal_program, flags)
+        $CPPFLAGS << flags
+
+        true
+      end
+    end
+  end
+end
+
 create_makefile 'charlock_holmes/charlock_holmes'