Add a friendly comment at the top of auto-generated C files.

descriptor/descriptor.c

@@ -1,4 +1,16 @@
-/* This file was generated by upbc (the upb compiler).  Do not edit. */
+/*
+ * This file is a data dump of a protocol buffer into a C structure.
+ * It was created by the upb compiler (upbc) with the following
+ * command-line:
+ *
+ *   ./tools/upbc -i upb_file_descriptor_set -o descriptor/descriptor descriptor/descriptor.proto.pb
+ *
+ * This file is a dump of 'descriptor/descriptor.proto.pb'.
+ * It contains exactly the same data, but in a C structure form
+ * instead of a serialized protobuf.  This file contains no code,
+ * only data.
+ *
+ * This file was auto-generated.  Do not edit. */
 
 #include "descriptor/descriptor.h"
 

tools/upbc.c

@@ -372,10 +372,30 @@ static void add_submsgs(void *data, struct upb_msg *m, struct upb_strtable *t)
 /* write_messages_c emits a .c file that contains the data of a protobuf,
  * serialized as C structures. */
 static void write_message_c(void *data, struct upb_msg *m,
-                            char *cident, char *hfile_name, FILE *stream)
+                            char *cident, char *hfile_name,
+                            int argc, char *argv[], char *infile_name,
+                            FILE *stream)
 {
-  fputs("/* This file was generated by upbc (the upb compiler).  "
-        "Do not edit. */\n\n", stream),
+  fputs(
+    "/*\n"
+    " * This file is a data dump of a protocol buffer into a C structure.\n"
+    " * It was created by the upb compiler (upbc) with the following\n"
+    " * command-line:\n"
+    " *\n", stream);
+  fputs(" *   ", stream);
+  for(int i = 0; i < argc; i++) {
+    fputs(argv[i], stream);
+    if(i < argc-1) fputs(" ", stream);
+  }
+  fputs("\n *\n", stream);
+  fprintf(stream, " * This file is a dump of '%s'.\n", infile_name);
+  fputs(
+    " * It contains exactly the same data, but in a C structure form\n"
+    " * instead of a serialized protobuf.  This file contains no code,\n"
+    " * only data.\n"
+    " *\n"
+    " * This file was auto-generated.  Do not edit. */\n\n", stream);
+
   fprintf(stream, "#include \"%s\"\n\n", hfile_name);
 
   /* Gather all strings into a giant string.  Use a hash to prevent adding the
@@ -652,7 +672,7 @@ int main(int argc, char *argv[])
   if(cident) {
     FILE *c_file = fopen(c_filename, "w");
     if(!c_file) error("Failed to open .h output file");
-    write_message_c(fds, c.fds_msg, cident, h_filename, c_file);
+    write_message_c(fds, c.fds_msg, cident, h_filename, argc, argv, input_file, c_file);
     fclose(c_file);
   }
   upb_context_free(&c);