Add -M option

main.c

@@ -10,6 +10,7 @@ bool opt_fcommon = true;
 static FileType opt_x;
 static StringArray opt_include;
 static bool opt_E;
+static bool opt_M;
 static bool opt_S;
 static bool opt_c;
 static bool opt_cc1;
@@ -176,6 +177,11 @@ static void parse_args(int argc, char **argv) {
       continue;
     }
 
+    if (!strcmp(argv[i], "-M")) {
+      opt_M = true;
+      continue;
+    }
+
     if (!strcmp(argv[i], "-cc1-input")) {
       base_file = argv[++i];
       continue;
@@ -326,6 +332,20 @@ static void print_tokens(Token *tok) {
   fprintf(out, "\n");
 }
 
+// If -M options is given, the compiler write a list of input files to
+// stdout in a format that "make" command can read. This feature is
+// used to automate file dependency management.
+static void print_dependencies(void) {
+  FILE *out = open_file(opt_o ? opt_o : "-");
+  fprintf(out, "%s:", replace_extn(base_file, ".o"));
+
+  File **files = get_input_files();
+
+  for (int i = 0; files[i]; i++)
+    fprintf(out, " \\\n  %s", files[i]->name);
+  fprintf(out, "\n\n");
+}
+
 static Token *must_tokenize_file(char *path) {
   Token *tok = tokenize_file(path);
   if (!tok)
@@ -369,6 +389,12 @@ static void cc1(void) {
   tok = append_tokens(tok, tok2);
   tok = preprocess(tok);
 
+  // If -M is given, print file dependencies.
+  if (opt_M) {
+    print_dependencies();
+    return;
+  }
+
   // If -E is given, print out preprocessed C code as a result.
   if (opt_E) {
     print_tokens(tok);
@@ -551,7 +577,7 @@ int main(int argc, char **argv) {
     assert(type == FILE_C);
 
     // Just preprocess
-    if (opt_E) {
+    if (opt_E || opt_M) {
       run_cc1(argc, argv, input, NULL);
       continue;
     }

test/driver.sh

@@ -221,4 +221,11 @@ check '.so'
 $chibicc -hashmap-test
 check 'hashmap'
 
+# -M
+echo '#include "out2.h"' > $tmp/out.c
+echo '#include "out3.h"' >> $tmp/out.c
+touch $tmp/out2.h $tmp/out3.h
+$chibicc -M -I$tmp $tmp/out.c | grep -q -z '^out.o: .*/out\.c .*/out2\.h .*/out3\.h'
+check -M
+
 echo OK