ls-tree: default <tree-ish> to HEAD

When no positional arguments are passed to `git ls-tree`, it currently
prints "usage" info to stderr and exits with code 129. A more intuitive
default would be to operate on the `HEAD` commit's tree (similarly to
`git show`, `git log`, and possibly others).

This patch updates `git ls-tree [options...]` to operate identically to
`git ls-tree [options...] HEAD`, updates the docs to reflect that
`<tree-ish>` is optional (and `[path...]` args can only be provided if a
`<tree-ish>` is explicitly provided first), and duplicates some existing
test cases to omit the `HEAD` argument to `ls-tree` (verifying that
`ls-tree` behaves identically whether `HEAD` is provided or not).

Signed-off-by: Ryan Williams <[email protected]>

Documentation/git-ls-tree.txt

@@ -11,7 +11,7 @@ SYNOPSIS
 [verse]
 'git ls-tree' [-d] [-r] [-t] [-l] [-z]
 	    [--name-only] [--name-status] [--object-only] [--full-name] [--full-tree] [--abbrev[=<n>]] [--format=<format>]
-	    <tree-ish> [<path>...]
+	    [<tree-ish> [<path>...]]
 
 DESCRIPTION
 -----------
@@ -36,7 +36,7 @@ in the current working directory.  Note that:
 OPTIONS
 -------
 <tree-ish>::
-	Id of a tree-ish.
+	Id of a tree-ish. If omitted, defaults to "HEAD".
 
 -d::
 	Show only the named tree entry itself, not its children.
@@ -139,7 +139,7 @@ which is able to interpolate different fields using a `%(fieldname)` notation.
 For example, if you only care about the "objectname" and "path" fields, you
 can execute with a specific "--format" like
 
-	git ls-tree --format='%(objectname) %(path)' <tree-ish>
+	git ls-tree --format='%(objectname) %(path)' [<tree-ish>]
 
 FIELD NAMES
 -----------

builtin/ls-tree.c

@@ -18,7 +18,7 @@
 #include "pathspec.h"
 
 static const char * const ls_tree_usage[] = {
-	N_("git ls-tree [<options>] <tree-ish> [<path>...]"),
+	N_("git ls-tree [<options>] [<tree-ish> [<path>...]]"),
 	NULL
 };
 
@@ -377,6 +377,7 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 	};
 	struct ls_tree_cmdmode_to_fmt *m2f = ls_tree_cmdmode_format;
 	int ret;
+	const char* fallback_argv[] = { "HEAD", NULL };
 
 	git_config(git_default_config, NULL);
 
@@ -405,8 +406,13 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 		usage_msg_opt(
 			_("--format can't be combined with other format-altering options"),
 			ls_tree_usage, ls_tree_options);
-	if (argc < 1)
-		usage_with_options(ls_tree_usage, ls_tree_options);
+
+	/* If no positional args were passed, default <tree-ish> to HEAD. */
+	if (argc < 1) {
+		argv = fallback_argv;
+		argc = 1;
+	}
+
 	if (repo_get_oid(the_repository, argv[0], &oid))
 		die("Not a valid object name %s", argv[0]);
 

t/t3105-ls-tree-output.sh

@@ -26,11 +26,16 @@ test_ls_tree_format_mode_output () {
 		local mode="$1" &&
 		shift &&
 
-		test_expect_success "'ls-tree $opts${mode:+ $mode}' output" '
+		test_expect_success "'ls-tree ${mode:+$mode }$opts' output" '
 			git ls-tree ${mode:+$mode }$opts HEAD >actual &&
 			test_cmp expect actual
 		'
 
+		test_expect_success "'ls-tree ${mode:+$mode }$opts' (default HEAD) output" '
+			git ls-tree ${mode:+$mode }$opts >actual &&
+			test_cmp expect actual
+		'
+
 		case "$opts" in
 		--full-tree)
 			test_expect_success "'ls-tree $opts${mode:+ $mode}' output (via subdir, fails)" '