Teach fast-import to honor pack.compression and pack.depth

We now use the configured pack.compression and pack.depth values
within fast-import, as like builtin-pack-objects fast-import is
generating a packfile for consumption by the Git tools.

We use the same behavior as builtin-pack-objects does for these
options, allowing core.compression to supply the default value
for pack.compression.

The default setting for pack.depth within fast-import is still 10
as users will generally repack fast-import generated packfiles by
`repack -f`.  A large delta depth within the fast-import packfile
can significantly slow down such a later repack.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fast-import.c

@@ -275,6 +275,8 @@ struct recent_command
 static unsigned long max_depth = 10;
 static off_t max_packsize = (1LL << 32) - 1;
 static int force_update;
+static int pack_compression_level = Z_DEFAULT_COMPRESSION;
+static int pack_compression_seen;
 
 /* Stats and misc. counters */
 static uintmax_t alloc_count;
@@ -1038,7 +1040,7 @@ static int store_object(
 		delta = NULL;
 
 	memset(&s, 0, sizeof(s));
-	deflateInit(&s, zlib_compression_level);
+	deflateInit(&s, pack_compression_level);
 	if (delta) {
 		s.next_in = delta;
 		s.avail_in = deltalen;
@@ -1066,7 +1068,7 @@ static int store_object(
 			delta = NULL;
 
 			memset(&s, 0, sizeof(s));
-			deflateInit(&s, zlib_compression_level);
+			deflateInit(&s, pack_compression_level);
 			s.next_in = (void *)dat->buf;
 			s.avail_in = dat->len;
 			s.avail_out = deflateBound(&s, s.avail_in);
@@ -2282,6 +2284,27 @@ static void import_marks(const char *input_file)
 	fclose(f);
 }
 
+static int git_pack_config(const char *k, const char *v)
+{
+	if (!strcmp(k, "pack.depth")) {
+		max_depth = git_config_int(k, v);
+		if (max_depth > MAX_DEPTH)
+			max_depth = MAX_DEPTH;
+		return 0;
+	}
+	if (!strcmp(k, "pack.compression")) {
+		int level = git_config_int(k, v);
+		if (level == -1)
+			level = Z_DEFAULT_COMPRESSION;
+		else if (level < 0 || level > Z_BEST_COMPRESSION)
+			die("bad pack compression level %d", level);
+		pack_compression_level = level;
+		pack_compression_seen = 1;
+		return 0;
+	}
+	return git_default_config(k, v);
+}
+
 static const char fast_import_usage[] =
 "git-fast-import [--date-format=f] [--max-pack-size=n] [--depth=n] [--active-branches=n] [--export-marks=marks.file]";
 
@@ -2289,7 +2312,10 @@ int main(int argc, const char **argv)
 {
 	unsigned int i, show_stats = 1;
 
-	git_config(git_default_config);
+	git_config(git_pack_config);
+	if (!pack_compression_seen && core_compression_seen)
+		pack_compression_level = core_compression_level;
+
 	alloc_objects(object_entry_alloc);
 	strbuf_init(&command_buf, 0);
 	atom_table = xcalloc(atom_table_sz, sizeof(struct atom_str*));