tcc: Draft suppoprt for -MD/-MF options

In build systems, this is used to automatically collect target
dependencies, e.g.

    ---- 8< (hello.c) ----
    #include "hello.h"
    #include <stdio.h>

    int main()
    {
        printf("Hello World!\n");
        return 0;
    }

$ tcc -MD -c hello.c    # -> hello.o, hello.d
$ cat hello.d
hello.o : \
        hello.c \
        hello.h \
        /usr/include/stdio.h \
        /usr/include/features.h \
        /usr/include/bits/predefs.h \
        /usr/include/sys/cdefs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs-32.h \
        /home/kirr/local/tcc/lib/tcc/include/stddef.h \
        /usr/include/bits/types.h \
        /usr/include/bits/wordsize.h \
        /usr/include/bits/typesizes.h \
        /usr/include/libio.h \
        /usr/include/_G_config.h \
        /usr/include/wchar.h \
        /home/kirr/local/tcc/lib/tcc/include/stdarg.h \
        /usr/include/bits/stdio_lim.h \
        /usr/include/bits/sys_errlist.h \

NOTE: gcc supports -MD only for .c -> .o, but in tcc, we generate
dependencies for whatever action is being taken. E.g. for .c -> exe, the
result will be:

$ tcc -MD -o hello hello.c  # -> hello, hello.d
hello: \
        /usr/lib/crt1.o \
        /usr/lib/crti.o \
        hello.c \
        hello.h \
        /usr/include/stdio.h \
        /usr/include/features.h \
        /usr/include/bits/predefs.h \
        /usr/include/sys/cdefs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs-32.h \
        /home/kirr/local/tcc/lib/tcc/include/stddef.h \
        /usr/include/bits/types.h \
        /usr/include/bits/wordsize.h \
        /usr/include/bits/typesizes.h \
        /usr/include/libio.h \
        /usr/include/_G_config.h \
        /usr/include/wchar.h \
        /home/kirr/local/tcc/lib/tcc/include/stdarg.h \
        /usr/include/bits/stdio_lim.h \
        /usr/include/bits/sys_errlist.h \
        /usr/lib/libc.so \
        /lib/libc.so.6 \
        /usr/lib/ld-linux.so.2 \
        /lib/ld-linux.so.2 \
        /usr/lib/libc_nonshared.a \
        /lib/libc.so.6 \
        /usr/lib/libc_nonshared.a \
        /home/kirr/local/tcc/lib/tcc/libtcc1.a \
        /usr/lib/crtn.o \

So tcc dependency generator is a bit more clever than one used in gcc :)

Also, I've updated TODO and Changelog (in not-yet-released section).

v2:

(Taking inputs from grischka and me myself)

- put code to generate deps file into a function.
- used tcc_fileextension() instead of open-coding
- generate deps only when compilation/preprocessing was successful

v3:

- use pstrcpy instead of snprintf(buf, sizeof(buf), "%s", ...)

libtcc.c

@@ -1041,6 +1041,7 @@ LIBTCCAPI void tcc_delete(TCCState *s1)
 
     dynarray_reset(&s1->input_files, &s1->nb_input_files);
     dynarray_reset(&s1->input_libs, &s1->nb_input_libs);
+    dynarray_reset(&s1->target_deps, &s1->nb_target_deps);
 
 #ifdef HAVE_SELINUX
     munmap (s1->write_mem, s1->mem_size);
@@ -1092,6 +1093,10 @@ ST_FUNC int tcc_add_file_internal(TCCState *s1, const char *filename, int flags)
         goto the_end;
     }
 
+    /* update target deps */
+    dynarray_add((void ***)&s1->target_deps, &s1->nb_target_deps,
+            tcc_strdup(filename));
+
     if (flags & AFF_PREPROCESS) {
         ret = tcc_preprocess(s1);
         goto the_end;
@@ -1585,3 +1590,37 @@ LIBTCCAPI const char *tcc_default_target(TCCState *s)
 
     return outfile_default;
 }
+
+
+LIBTCCAPI void tcc_gen_makedeps(TCCState *s, const char *target, const char *filename)
+{
+    FILE *depout;
+    char buf[1024], *ext;
+    int i;
+
+    if (!target)
+        target = tcc_default_target(s);
+
+    if (!filename) {
+        /* compute filename automatically
+         * dir/file.o -> dir/file.d             */
+        pstrcpy(buf, sizeof(buf), target);
+        ext = tcc_fileextension(buf);
+        pstrcpy(ext, sizeof(buf) - (ext-buf), ".d");
+        filename = buf;
+    }
+
+    if (s->verbose)
+        printf("<- %s\n", filename);
+
+    /* XXX return err codes instead of error() ? */
+    depout = fopen(filename, "w");
+    if (!depout)
+        error("could not open '%s'", filename);
+
+    fprintf(depout, "%s : \\\n", target);
+    for (i=0; i<s->nb_target_deps; ++i)
+        fprintf(depout, "\t%s \\\n", s->target_deps[i]);
+    fprintf(depout, "\n");
+    fclose(depout);
+}