Consistent behavior with missing or incorrect parameters

include/platform.h

@@ -73,8 +73,10 @@
 #if defined(_MSC_VER) || defined(__MINGW32__)
 # include <io.h>
 # define setmode(fd, mode) _setmode(fd, mode)
+# define isatty(fd) _isatty(fd)
 #else
 # define setmode(fd, mode) (0)
+# define isatty(fd) (0)
 #endif
 
 #endif // RGBDS_PLATFORM_H

src/asm/main.c

@@ -126,7 +126,7 @@ static struct option const longopts[] = {
 	{ NULL,               no_argument,       NULL,     0   }
 };
 
-static void print_usage(void)
+_Noreturn static void print_usage(void)
 {
 	fputs(
 "Usage: rgbasm [-EHhLlVvw] [-b chars] [-D name[=value]] [-g chars] [-I path]\n"

src/fix/main.c

@@ -62,7 +62,7 @@ static struct option const longopts[] = {
 	{ NULL,               no_argument,       NULL, 0   }
 };
 
-static void printUsage(void)
+_Noreturn static void printUsage(void)
 {
 	fputs(
 "Usage: rgbfix [-jOsVv] [-C | -c] [-f <fix_spec>] [-i <game_id>] [-k <licensee>]\n"
@@ -78,6 +78,7 @@ static void printUsage(void)
 "\n"
 "For help, use `man rgbfix' or go to https://rgbds.gbdev.io/docs/\n",
 	      stderr);
+	exit(1);
 }
 
 static uint8_t nbErrors;
@@ -1401,9 +1402,7 @@ do { \
 			break;
 
 		default:
-			fprintf(stderr, "FATAL: unknown option '%c'\n", ch);
 			printUsage();
-			exit(1);
 		}
 #undef parseByte
 	}
@@ -1443,6 +1442,10 @@ do { \
 	bool failed = nbErrors;
 
 	if (!*argv) {
+		if (isatty(STDIN_FILENO)) {
+			fputs("FATAL: Please specify an input file (pass `-` to read from standard input)\n", stderr);
+			printUsage();
+		}
 		failed |= processFilename("-");
 	} else {
 		do {

src/gfx/main.cpp

@@ -139,7 +139,7 @@ static struct option const longopts[] = {
     {NULL,                 no_argument,       NULL, 0  }
 };
 
-static void printUsage(void) {
+[[noreturn]] static void printUsage(void) {
 	fputs("Usage: rgbgfx [-r stride] [-CmuVZ] [-v [-v ...]] [-a <attr_map> | -A]\n"
 	      "       [-b <base_ids>] [-c <colors>] [-d <depth>] [-L <slice>] [-N <nb_tiles>]\n"
 	      "       [-n <nb_pals>] [-o <out_file>] [-p <pal_file> | -P] [-q <pal_map> | -Q]\n"
@@ -241,11 +241,9 @@ static void registerInput(char const *arg) {
 		        "\"%s\")\n",
 		        options.input.c_str(), arg);
 		printUsage();
-		exit(1);
 	} else if (arg[0] == '\0') { // Empty input path
 		fprintf(stderr, "FATAL: input image path cannot be empty!\n");
 		printUsage();
-		exit(1);
 	} else {
 		options.input = arg;
 	}
@@ -573,7 +571,6 @@ static char *parseArgv(int argc, char **argv, bool &autoAttrmap, bool &autoTilem
 			break;
 		default:
 			printUsage();
-			exit(1);
 		}
 	}
 
@@ -769,7 +766,8 @@ int main(int argc, char *argv[]) {
 	}
 
 	if (options.input.empty()) {
-		fatal("No input image specified");
+		fputs("FATAL: No input image specified\n", stderr);
+		printUsage();
 	}
 
 	// Do not do anything if option parsing went wrong

src/link/main.c

@@ -196,8 +196,7 @@ static struct option const longopts[] = {
 	{ NULL,            no_argument,       NULL, 0   }
 };
 
-// Prints the program's usage to stdout.
-static void printUsage(void)
+_Noreturn static void printUsage(void)
 {
 	fputs(
 "Usage: rgblink [-dMtVvwx] [-l script] [-m map_file] [-n sym_file]\n"
@@ -214,6 +213,7 @@ static void printUsage(void)
 "\n"
 "For help, use `man rgblink' or go to https://rgbds.gbdev.io/docs/\n",
 	      stderr);
+	exit(1);
 }
 
 // Cleans up what has been done
@@ -435,17 +435,15 @@ int main(int argc, char *argv[])
 			break;
 		default:
 			printUsage();
-			exit(1);
 		}
 	}
 
 	int curArgIndex = musl_optind;
 
 	// If no input files were specified, the user must have screwed up
 	if (curArgIndex == argc) {
-		fputs("FATAL: no input files\n", stderr);
+		fputs("FATAL: Please specify an input file (pass `-` to read from standard input)\n", stderr);
 		printUsage();
-		exit(1);
 	}
 
 	// Patch the size array depending on command-line options