add an extra level of indirection to main()

There are certain startup tasks that we expect every git
process to do. In some cases this is just to improve the
quality of the program (e.g., setting up gettext()). In
others it is a requirement for using certain functions in
libgit.a (e.g., system_path() expects that you have called
git_extract_argv0_path()).

Most commands are builtins and are covered by the git.c
version of main(). However, there are still a few external
commands that use their own main(). Each of these has to
remember to include the correct startup sequence, and we are
not always consistent.

Rather than just fix the inconsistencies, let's make this
harder to get wrong by providing a common main() that can
run this standard startup.

We basically have two options to do this:

 - the compat/mingw.h file already does something like this by
   adding a #define that replaces the definition of main with a
   wrapper that calls mingw_startup().

   The upside is that the code in each program doesn't need
   to be changed at all; it's rewritten on the fly by the
   preprocessor.

   The downside is that it may make debugging of the startup
   sequence a bit more confusing, as the preprocessor is
   quietly inserting new code.

 - the builtin functions are all of the form cmd_foo(),
   and git.c's main() calls them.

   This is much more explicit, which may make things more
   obvious to somebody reading the code. It's also more
   flexible (because of course we have to figure out _which_
   cmd_foo() to call).

   The downside is that each of the builtins must define
   cmd_foo(), instead of just main().

This patch chooses the latter option, preferring the more
explicit approach, even though it is more invasive. We
introduce a new file common-main.c, with the "real" main. It
expects to call cmd_main() from whatever other objects it is
linked against.

We link common-main.o against anything that links against
libgit.a, since we know that such programs will need to do
this setup. Note that common-main.o can't actually go inside
libgit.a, as the linker would not pick up its main()
function automatically (it has no callers).

The rest of the patch is just adjusting all of the various
external programs (mostly in t/helper) to use cmd_main().
I've provided a global declaration for cmd_main(), which
means that all of the programs also need to match its
signature. In particular, many functions need to switch to
"const char **" instead of "char **" for argv. This effect
ripples out to a few other variables and functions, as well.

This makes the patch even more invasive, but the end result
is much better. We should be treating argv strings as const
anyway, and now all programs conform to the same signature
(which also matches the way builtins are defined).

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

Makefile

@@ -943,7 +943,7 @@ BUILTIN_OBJS += builtin/verify-tag.o
 BUILTIN_OBJS += builtin/worktree.o
 BUILTIN_OBJS += builtin/write-tree.o
 
-GITLIBS = $(LIB_FILE) $(XDIFF_LIB)
+GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB)
 EXTLIBS =
 
 GIT_USER_AGENT = git/$(GIT_VERSION)
@@ -1572,7 +1572,15 @@ TCLTK_PATH_SQ = $(subst ','\'',$(TCLTK_PATH))
 DIFF_SQ = $(subst ','\'',$(DIFF))
 PERLLIB_EXTRA_SQ = $(subst ','\'',$(PERLLIB_EXTRA))
 
-LIBS = $(GITLIBS) $(EXTLIBS)
+# We must filter out any object files from $(GITLIBS),
+# as it is typically used like:
+#
+#   foo: foo.o $(GITLIBS)
+#	$(CC) $(filter %.o,$^) $(LIBS)
+#
+# where we use it as a dependency. Since we also pull object files
+# from the dependency list, that would make each entry appear twice.
+LIBS = $(filter-out %.o, $(GITLIBS)) $(EXTLIBS)
 
 BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
 	$(COMPAT_CFLAGS)
@@ -1708,8 +1716,8 @@ git.sp git.s git.o: EXTRA_CPPFLAGS = \
 	'-DGIT_INFO_PATH="$(infodir_relative_SQ)"'
 
 git$X: git.o GIT-LDFLAGS $(BUILTIN_OBJS) $(GITLIBS)
-	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) git.o \
-		$(BUILTIN_OBJS) $(LIBS)
+	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
+		$(filter %.o,$^) $(LIBS)
 
 help.sp help.s help.o: common-cmds.h
 
@@ -1902,6 +1910,7 @@ TEST_OBJS := $(patsubst test-%$X,test-%.o,$(TEST_PROGRAMS))
 OBJECTS := $(LIB_OBJS) $(BUILTIN_OBJS) $(PROGRAM_OBJS) $(TEST_OBJS) \
 	$(XDIFF_OBJS) \
 	$(VCSSVN_OBJS) \
+	common-main.o \
 	git.o
 ifndef NO_CURL
 	OBJECTS += http.o http-walker.o remote-curl.o

common-main.c

@@ -0,0 +1,12 @@
+#include "git-compat-util.h"
+
+int main(int argc, char **av)
+{
+	/*
+	 * This const trickery is explained in
+	 * 84d32bf7678259c08406571cd6ce4b7a6724dcba
+	 */
+	const char **argv = (const char **)av;
+
+	return cmd_main(argc, argv);
+}

credential-cache--daemon.c

@@ -257,7 +257,7 @@ static void init_socket_directory(const char *path)
 	free(path_copy);
 }
 
-int main(int argc, const char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	const char *socket_path;
 	int ignore_sighup = 0;

credential-cache.c

@@ -83,7 +83,7 @@ static void do_cache(const char *socket, const char *action, int timeout,
 	strbuf_release(&buf);
 }
 
-int main(int argc, const char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	char *socket_path = NULL;
 	int timeout = 900;

credential-store.c

@@ -142,7 +142,7 @@ static void lookup_credential(const struct string_list *fns, struct credential *
 			return; /* Found credential */
 }
 
-int main(int argc, char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	const char * const usage[] = {
 		"git credential-store [<options>] <action>",

daemon.c

@@ -32,7 +32,7 @@ static const char daemon_usage[] =
 "           [<directory>...]";
 
 /* List of acceptable pathname prefixes */
-static char **ok_paths;
+static const char **ok_paths;
 static int strict_paths;
 
 /* If this is set, git-daemon-export-ok is not required */
@@ -240,7 +240,7 @@ static const char *path_ok(const char *directory, struct hostinfo *hi)
 	}
 
 	if ( ok_paths && *ok_paths ) {
-		char **pp;
+		const char **pp;
 		int pathlen = strlen(path);
 
 		/* The validation is done on the paths after enter_repo
@@ -1178,7 +1178,7 @@ static int serve(struct string_list *listen_addr, int listen_port,
 	return service_loop(&socklist);
 }
 
-int main(int argc, char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	int listen_port = 0;
 	struct string_list listen_addr = STRING_LIST_INIT_NODUP;
@@ -1193,7 +1193,7 @@ int main(int argc, char **argv)
 	git_extract_argv0_path(argv[0]);
 
 	for (i = 1; i < argc; i++) {
-		char *arg = argv[i];
+		const char *arg = argv[i];
 		const char *v;
 
 		if (skip_prefix(arg, "--listen=", &v)) {

fast-import.c

@@ -300,7 +300,7 @@ static int failure;
 static FILE *pack_edges;
 static unsigned int show_stats = 1;
 static int global_argc;
-static char **global_argv;
+static const char **global_argv;
 
 /* Memory pools */
 static size_t mem_pool_alloc = 2*1024*1024 - sizeof(struct mem_pool);
@@ -3381,7 +3381,7 @@ static void parse_argv(void)
 		read_marks();
 }
 
-int main(int argc, char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	unsigned int i;
 

git-compat-util.h

@@ -1043,3 +1043,5 @@ struct tm *git_gmtime_r(const time_t *, struct tm *);
 #endif
 
 #endif
+
+extern int cmd_main(int, const char **);

git.c

@@ -630,9 +630,8 @@ static void restore_sigpipe_to_default(void)
 	signal(SIGPIPE, SIG_DFL);
 }
 
-int main(int argc, char **av)
+int cmd_main(int argc, const char **argv)
 {
-	const char **argv = (const char **) av;
 	const char *cmd;
 	int done_help = 0;
 

http-backend.c

@@ -632,7 +632,7 @@ static struct service_cmd {
 	{"POST", "/git-receive-pack$", service_rpc}
 };
 
-int main(int argc, char **argv)
+int cmd_main(int argc, const char **argv)
 {
 	char *method = getenv("REQUEST_METHOD");
 	char *dir;