git-rev-list: make --dense the default (and introduce "--sparse")

This actually does three things:

 - make "--dense" the default for git-rev-list. Since dense is a no-op if 
   no filenames are given, this doesn't actually change any historical 
   behaviour, but it's logically the right default (if we want to prune on 
   filenames, do it fully. The sparse "merge-only" thing may be useful, 
   but it's not what you'd normally expect)

 - make "git-rev-parse" show the default revision control before it shows 
   any pathnames.

   This was a real bug, but nobody would ever have noticed, because 
   the default thing tends to only make sense for git-rev-list, and 
   git-rev-list didn't use to take pathnames.

 - it changes "git-rev-list" to match the other commands that take a mix 
   of revisions and filenames - it no longer requires the "--" before 
   filenames (although you still need to do it if a filename could be 
   confused with a revision name, eg "gitk" in the git archive)

This all just makes for much more pleasant and obvous usage. Just doing a

	gitk t/

does the obvious thing: it will show the history as it concerns the "t/" 
subdirectory.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

NOTE! None of this will change anything that used to work before. But 
things that used to make git-rev-list die with a usage message will now 
possibly do things. In particular, it may do something that you don't 
expect.

For example, let's say that you mis-type a revision name, and do

	gitk v0.99.88

with one "8" too much. It used to cause gitk to die on you, echoing the 
usage string from git-rev-list. Now it will cause gitk to start up 
happily, and say "No commits selected", because there is no _file_ called 
"v0.99.88" anywhere, so git-rev-list will end up with empty output.

So it does change behaviour, even if it doesn't change anything that was 
_successful_ before.

For the same reasons, a

	git-rev-list $(git-rev-parse --default HEAD v0.99.88)

will now give an empty list rather than an error usage string.

(But doing

	git-rev-list v0.99.88

will still cause an error, since that doesn't have any revision at all!)

Comments? It really makes usage more "obvious", I think.

diff --git a/rev-list.c b/rev-list.c
index edf3b37..ac7a47f 100644
--- a/rev-list.c
+++ b/rev-list.c

@@ -28,7 +28,7 @@ static const char rev_list_usage[] =
 		      "  --merge-order [ --show-breaks ]\n"
 		      "  --topo-order";
 
-static int dense = 0;
+static int dense = 1;
 static int unpacked = 0;
 static int bisect_list = 0;
 static int tag_objects = 0;

@@ -619,7 +619,7 @@ static struct commit *get_commit_referen
 	struct object *object;
 
 	if (get_sha1(name, sha1))
-		usage(rev_list_usage);
+		return NULL;
 	object = parse_object(sha1);
 	if (!object)
 		die("bad object %s", name);

@@ -793,12 +793,12 @@ int main(int argc, const char **argv)
 			dense = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--sparse")) {
+			dense = 0;
+			continue;
+		}
 		if (!strcmp(arg, "--")) {
-			paths = get_pathspec(prefix, argv + i + 1);
-			if (paths) {
-				limited = 1;
-				diff_tree_setup_paths(paths);
-			}
+			i++;
 			break;
 		}
 

@@ -830,9 +830,20 @@ int main(int argc, const char **argv)
 			limited = 1;
 		}
 		commit = get_commit_reference(arg, flags);
+		if (!commit)
+			break;
 		handle_one_commit(commit, &list);
 	}
 
+	if (!list)
+		usage(rev_list_usage);
+
+	paths = get_pathspec(prefix, argv + i);
+	if (paths) {
+		limited = 1;
+		diff_tree_setup_paths(paths);
+	}
+
 	save_commit_buffer = verbose_header;
 	track_object_refs = 0;
 

diff --git a/rev-parse.c b/rev-parse.c
index 243f89f..adfc68c 100644
--- a/rev-parse.c
+++ b/rev-parse.c

@@ -153,6 +153,7 @@ static void show_datestring(const char *
 
 static void show_file(const char *arg)
 {
+	show_default();
 	if ((filter & (DO_NONFLAGS|DO_NOREV)) == (DO_NONFLAGS|DO_NOREV))
 		show(arg);
 }

@@ -174,7 +175,6 @@ int main(int argc, char **argv)
 		if (*arg == '-') {
 			if (!strcmp(arg, "--")) {
 				as_is = 1;
-				show_default();
 				/* Pass on the "--" if we show anything but files.. */
 				if (filter & (DO_FLAGS | DO_REVS))
 					show_file(arg);

On Tue, 25 Oct 2005, Linus Torvalds wrote:

This actually does three things:

 - make "--dense" the default for git-rev-list. Since dense is a no-op if 
   no filenames are given, this doesn't actually change any historical 
   behaviour, but it's logically the right default (if we want to prune on 
   filenames, do it fully. The sparse "merge-only" thing may be useful, 
   but it's not what you'd normally expect)

 - make "git-rev-parse" show the default revision control before it shows 
   any pathnames.

Btw, if it wasn't obvious, this has some subtle (and very nice) side 
effects.

For example, try this:

	git log git-fetch.sh

and notice how "git log" automagically became able to give per-file logs. 
With _zero_ changes to git-log.sh itself ;)

And same old rev-confusion-avoidance:

	git log -- gitk

to make clear that you want to get the log of "gitk the file", rather than 
"gitk the branch".

Magic. 

		Linus