Re: [PATCH 0/3] support `--oid-only` in `ls-tree`

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Mon, Nov 15 2021, Jeff King wrote:

> On Mon, Nov 15, 2021 at 04:13:24PM +0100, Ævar Arnfjörð Bjarmason wrote:
>
>> But I'd much rather see this be done with adding strbuf_expand() to
>> ls-tree. I.e. its docs say that it can emit:
>
> I had a similar thought, but that's a much bigger task. I think it would
> be reasonable to add --oid-only to match the existing --name-only, etc.
> If we later add a custom --format option, then it can easily be folded
> in and explained as "this is an alias for --format=%(objectname)", just
> like --name-only would become "this is an alias for --format=%(path)".

A quick patch to do it below, seems to work, passes all tests, but I
don't know how much I'd trust it. It's also quite an add use of
strbuf_expa(). We print to stdout directly since
write_name_quoted_relative() really wants to write to stdout, and not
give you a buffer. But I guess it makes sense in a way.

The hardcoded %7s for %(objectsize) is a bit nasty, but I don't know if
we've got anything existing that handles format specifiers with
strbuf_expand() that we could steal.

I really wouldn't trust this code much, I found it when writing it that
our tests for ls-tree are really lacking, e.g. we may not have a single
test for "-l" anywhere (or maybe I didn't look enough, I was just
running t/*ls*tree* while hacking it.

I do thin that we should consider just going with --format in either
case if we agree that this is a good direction. I.e. could just support
3-4 hardcoded formats now and die if anything else is specified.

Then we'd be future-proof with the same interface expanding later, and
wouldn't need to support options that we're only carrying because we
didn't implement the more generic format support.

(Assume my Signed-off-by, if there's any interest...)

diff --git a/builtin/ls-tree.c b/builtin/ls-tree.c
index 3a442631c71..e89daad4229 100644
--- a/builtin/ls-tree.c
+++ b/builtin/ls-tree.c
@@ -31,6 +31,20 @@ static const  char * const ls_tree_usage[] = {
 	NULL
 };
 
+static const char *ls_tree_format_d = "%(objectmode) %(objecttype) %(objectname)	%(path)";
+static const char *ls_tree_format_l = "%(objectmode) %(objecttype) %(objectname) %(objectsize)	%(path)";
+static const char *ls_tree_format_n = "%(path)";
+
+struct expand_ls_tree_data {
+	const char *format;
+	unsigned mode;
+	const char *type;
+	const struct object_id *oid;
+	int abbrev;
+	const char *pathname;
+	const char *basebuf;
+};
+
 static int show_recursive(const char *base, int baselen, const char *pathname)
 {
 	int i;
@@ -61,9 +75,69 @@ static int show_recursive(const char *base, int baselen, const char *pathname)
 	return 0;
 }
 
+static size_t expand_show_tree(struct strbuf *sb,
+			       const char *start,
+			       void *context)
+{
+	struct expand_ls_tree_data *data = context;
+	const char *end;
+	const char *p;
+	size_t len;
+	const char *type = blob_type;
+
+	if (sb->len) {
+		fputs(sb->buf, stdout);
+		strbuf_reset(sb);
+	}
+
+	if (*start != '(')
+		die(_("bad format as of '%s'"), start);
+	end = strchr(start + 1, ')');
+	if (!end)
+		die(_("ls-tree format element '%s' does not end in ')'"),
+		    start);
+	len = end - start + 1;
+
+	if (skip_prefix(start, "(objectmode)", &p)) {
+		printf("%06o", data->mode);
+	} else if (skip_prefix(start, "(objecttype)", &p)) {
+		fputs(data->type, stdout);
+	} else if (skip_prefix(start, "(objectsize)", &p)) {
+		char size_text[24];
+		const struct object_id *oid = data->oid;
+
+		if (!strcmp(type, blob_type)) {
+			unsigned long size;
+			if (oid_object_info(the_repository, oid, &size) == OBJ_BAD)
+				xsnprintf(size_text, sizeof(size_text),
+					  "BAD");
+			else
+				xsnprintf(size_text, sizeof(size_text),
+					  "%"PRIuMAX, (uintmax_t)size);
+		} else {
+			xsnprintf(size_text, sizeof(size_text), "-");
+		}
+		printf("%7s", size_text);
+	} else if (skip_prefix(start, "(objectname)", &p)) {
+		fputs(find_unique_abbrev(data->oid, data->abbrev), stdout);
+	} else if (skip_prefix(start, "(path)", &p)) {
+		write_name_quoted_relative(data->basebuf,
+					   chomp_prefix ? ls_tree_prefix : NULL,
+					   stdout, line_termination);
+
+	} else {
+		unsigned int errlen = (unsigned long)len;
+		die(_("bad ls-tree format specifiec %%%.*s"), errlen, start);	
+	}
+
+	return len;
+}
+
 static int show_tree(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, void *context)
 {
+	struct expand_ls_tree_data *data = context;
+	struct strbuf sb = STRBUF_INIT;
 	int retval = 0;
 	int baselen;
 	const char *type = blob_type;
@@ -90,31 +164,18 @@ static int show_tree(const struct object_id *oid, struct strbuf *base,
 	else if (ls_options & LS_TREE_ONLY)
 		return 0;
 
-	if (!(ls_options & LS_NAME_ONLY)) {
-		if (ls_options & LS_SHOW_SIZE) {
-			char size_text[24];
-			if (!strcmp(type, blob_type)) {
-				unsigned long size;
-				if (oid_object_info(the_repository, oid, &size) == OBJ_BAD)
-					xsnprintf(size_text, sizeof(size_text),
-						  "BAD");
-				else
-					xsnprintf(size_text, sizeof(size_text),
-						  "%"PRIuMAX, (uintmax_t)size);
-			} else
-				xsnprintf(size_text, sizeof(size_text), "-");
-			printf("%06o %s %s %7s\t", mode, type,
-			       find_unique_abbrev(oid, abbrev),
-			       size_text);
-		} else
-			printf("%06o %s %s\t", mode, type,
-			       find_unique_abbrev(oid, abbrev));
-	}
 	baselen = base->len;
 	strbuf_addstr(base, pathname);
-	write_name_quoted_relative(base->buf,
-				   chomp_prefix ? ls_tree_prefix : NULL,
-				   stdout, line_termination);
+
+	strbuf_reset(&sb);
+	data->mode = mode;
+	data->type = type;
+	data->oid = oid;
+	data->abbrev = abbrev;
+	data->pathname = pathname;
+	data->basebuf = base->buf;
+	strbuf_expand(&sb, data->format, expand_show_tree, data);
+
 	strbuf_setlen(base, baselen);
 	return retval;
 }
@@ -147,6 +208,9 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 		OPT__ABBREV(&abbrev),
 		OPT_END()
 	};
+	struct expand_ls_tree_data ls_tree_cb_data = {
+		.format = ls_tree_format_d,
+	};
 
 	git_config(git_default_config, NULL);
 	ls_tree_prefix = prefix;
@@ -161,8 +225,14 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 	}
 	/* -d -r should imply -t, but -d by itself should not have to. */
 	if ( (LS_TREE_ONLY|LS_RECURSIVE) ==
-	    ((LS_TREE_ONLY|LS_RECURSIVE) & ls_options))
+	    ((LS_TREE_ONLY|LS_RECURSIVE) & ls_options)) {
 		ls_options |= LS_SHOW_TREES;
+	}
+	if (ls_options & LS_NAME_ONLY)
+		ls_tree_cb_data.format = ls_tree_format_n;
+
+	if (ls_options & LS_SHOW_SIZE)
+		ls_tree_cb_data.format = ls_tree_format_l;
 
 	if (argc < 1)
 		usage_with_options(ls_tree_usage, ls_tree_options);
@@ -185,6 +255,7 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 	tree = parse_tree_indirect(&oid);
 	if (!tree)
 		die("not a tree object");
+
 	return !!read_tree(the_repository, tree,
-			   &pathspec, show_tree, NULL);
+			   &pathspec, show_tree, &ls_tree_cb_data);
 }