From a2b7a3b3a966c5801efe968d4b5656fa5a885409 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nguy=E1=BB=85n=20Th=C3=A1i=20Ng=E1=BB=8Dc=20Duy?=
 <pclouds@gmail.com>
Date: Thu, 3 Feb 2011 13:23:34 +0700
Subject: diff: support --cached on unborn branches
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

"git diff --cached" (without revision) used to mean "git diff --cached
HEAD" (i.e. the user was too lazy to type HEAD). This "correctly"
failed when there was no commit yet. But was that correctness useful?

This patch changes the definition of what particular command means.
It is a request to show what _would_ be committed without further "git
add". The internal implementation is the same "git diff --cached HEAD"
when HEAD exists, but when there is no commit yet, it compares the index
with an empty tree object to achieve the desired result.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-diff.txt b/Documentation/git-diff.txt
index f6ac847..4910510 100644
--- a/Documentation/git-diff.txt
+++ b/Documentation/git-diff.txt
@@ -38,6 +38,8 @@ directories. This behavior can be forced by --no-index.
 	commit relative to the named <commit>.  Typically you
 	would want comparison with the latest commit, so if you
 	do not give <commit>, it defaults to HEAD.
+	If HEAD does not exist (e.g. unborned branches) and
+	<commit> is not given, it shows all staged changes.
 	--staged is a synonym of --cached.
 
 'git diff' [--options] <commit> [--] [<path>...]::
diff --git a/builtin/diff.c b/builtin/diff.c
index 945e758..42822cd 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -330,8 +330,11 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 			else if (!strcmp(arg, "--cached") ||
 				 !strcmp(arg, "--staged")) {
 				add_head_to_pending(&rev);
-				if (!rev.pending.nr)
-					die("No HEAD commit to compare with (yet)");
+				if (!rev.pending.nr) {
+					struct tree *tree;
+					tree = lookup_tree((const unsigned char*)EMPTY_TREE_SHA1_BIN);
+					add_pending_object(&rev, &tree->object, "HEAD");
+				}
 				break;
 			}
 		}
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 9a66520..b8f81d0 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -290,4 +290,15 @@ test_expect_success 'log -S requires an argument' '
 	test_must_fail git log -S
 '
 
+test_expect_success 'diff --cached on unborn branch' '
+	echo ref: refs/heads/unborn >.git/HEAD &&
+	git diff --cached >result &&
+	test_cmp "$TEST_DIRECTORY/t4013/diff.diff_--cached" result
+'
+
+test_expect_success 'diff --cached -- file on unborn branch' '
+	git diff --cached -- file0 >result &&
+	test_cmp "$TEST_DIRECTORY/t4013/diff.diff_--cached_--_file0" result
+'
+
 test_done
diff --git a/t/t4013/diff.diff_--cached b/t/t4013/diff.diff_--cached
new file mode 100644
index 0000000..ff16e83
--- /dev/null
+++ b/t/t4013/diff.diff_--cached
@@ -0,0 +1,38 @@
+diff --git a/dir/sub b/dir/sub
+new file mode 100644
+index 0000000..992913c
+--- /dev/null
++++ b/dir/sub
+@@ -0,0 +1,8 @@
++A
++B
++C
++D
++E
++F
++1
++2
+diff --git a/file0 b/file0
+new file mode 100644
+index 0000000..10a8a9f
+--- /dev/null
++++ b/file0
+@@ -0,0 +1,9 @@
++1
++2
++3
++4
++5
++6
++A
++B
++C
+diff --git a/file1 b/file1
+new file mode 100644
+index 0000000..b1e6722
+--- /dev/null
++++ b/file1
+@@ -0,0 +1,3 @@
++A
++B
++C
diff --git a/t/t4013/diff.diff_--cached_--_file0 b/t/t4013/diff.diff_--cached_--_file0
new file mode 100644
index 0000000..b9bb858
--- /dev/null
+++ b/t/t4013/diff.diff_--cached_--_file0
@@ -0,0 +1,15 @@
+diff --git a/file0 b/file0
+new file mode 100644
+index 0000000..10a8a9f
+--- /dev/null
++++ b/file0
+@@ -0,0 +1,9 @@
++1
++2
++3
++4
++5
++6
++A
++B
++C
-- 
cgit v0.10.2-6-g49f6