Allow empty macro arguments, with a warning

Fixes #739

include/asm/lexer.h

@@ -67,6 +67,7 @@ enum LexerMode {
 };
 
 void lexer_SetMode(enum LexerMode mode);
+bool lexer_IsRawMode(void);
 void lexer_ToggleStringExpansion(bool enable);
 
 uint32_t lexer_GetIFDepth(void);

include/asm/macro.h

@@ -10,6 +10,7 @@
 #define RGBDS_MACRO_H
 
 #include <stdint.h>
+#include <stdbool.h>
 #include <stdlib.h>
 
 #include "asm/warning.h"
@@ -20,7 +21,7 @@ struct MacroArgs;
 
 struct MacroArgs *macro_GetCurrentArgs(void);
 struct MacroArgs *macro_NewArgs(void);
-void macro_AppendArg(struct MacroArgs **args, char *s);
+void macro_AppendArg(struct MacroArgs **args, char *s, bool isLastArg);
 void macro_UseNewArgs(struct MacroArgs *args);
 void macro_FreeArgs(struct MacroArgs *args);
 char const *macro_GetArg(uint32_t i);

include/asm/warning.h

@@ -20,6 +20,7 @@ enum WarningID {
 	WARNING_DIV,		      /* Division undefined behavior */
 	WARNING_EMPTY_DATA_DIRECTIVE, /* `db`, `dw` or `dl` directive without data in ROM */
 	WARNING_EMPTY_ENTRY,	      /* Empty entry in `db`, `dw` or `dl` */
+	WARNING_EMPTY_MACRO_ARG,      /* Empty macro argument */
 	WARNING_EMPTY_STRRPL,	      /* Empty second argument in `STRRPL` */
 	WARNING_LARGE_CONSTANT,	      /* Constants too large */
 	WARNING_LONG_STR,	      /* String too long for internal buffers */