[PATCH 1/3] Resurrect "diff-lib.c: adjust position of i-t-a entries in diff"

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

The original commit d95d728aba06a34394d15466045cbdabdada58a2 was
reverted in commit 78cc1a540ba127b13f2f3fd531777b57f3a9cd46 because we
were (and still are) not ready for a new world order. A lot more
investigation must be done to see what is impacted. See the 78cc1a5 for
details.

This patch takes a smaller and safer step. The new behavior is
controlled by shift_ita flag. We can gradually move more diff users to
the new behavior after we are sure it's safe to do so. This flag is
exposed to outside temporarily as "--shift-ita" for people who prefer
"git diff [--cached] --stat" to "git status"

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/diff-options.txt |  7 +++++++
 diff-lib.c                     | 12 ++++++++++++
 diff.c                         |  2 ++
 diff.h                         |  1 +
 t/t2203-add-intent.sh          | 20 ++++++++++++++++++--
 t/t7064-wtstatus-pv2.sh        |  4 ++--
 wt-status.c                    |  7 ++++++-
 7 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 7805a0c..e63285c 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -575,5 +575,12 @@ endif::git-format-patch[]
 --line-prefix=<prefix>::
 	Prepend an additional prefix to every line of output.
 
+--shift-ita::
+	By default entries added by "git add -N" appear as an existing
+	empty file in "git diff" and a new file in "git diff --cached".
+	This option makes the entry appear as a new file in "git diff"
+	and non-existent in "git diff --cached". Experimental option,
+	could be removed in future.
+
 For more detailed explanation on these common options, see also
 linkgit:gitdiffcore[7].
diff --git a/diff-lib.c b/diff-lib.c
index 3007c85..62d67c8 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -214,6 +214,11 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 					       !is_null_oid(&ce->oid),
 					       ce->name, 0);
 				continue;
+			} else if (revs->diffopt.shift_ita && ce_intent_to_add(ce)) {
+				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
+					       EMPTY_BLOB_SHA1_BIN, 0,
+					       ce->name, 0);
+				continue;
 			}
 
 			changed = match_stat_with_submodule(&revs->diffopt, ce, &st,
@@ -379,6 +384,13 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 	struct rev_info *revs = o->unpack_data;
 	int match_missing, cached;
 
+	/* i-t-a entries do not actually exist in the index */
+	if (revs->diffopt.shift_ita && idx && ce_intent_to_add(idx)) {
+		idx = NULL;
+		if (!tree)
+			return;	/* nothing to diff.. */
+	}
+
 	/* if the entry is not checked out, don't examine work tree */
 	cached = o->index_only ||
 		(idx && ((idx->ce_flags & CE_VALID) || ce_skip_worktree(idx)));
diff --git a/diff.c b/diff.c
index c6da383..4178689 100644
--- a/diff.c
+++ b/diff.c
@@ -3923,6 +3923,8 @@ int diff_opt_parse(struct diff_options *options,
 		return parse_submodule_opt(options, arg);
 	else if (skip_prefix(arg, "--ws-error-highlight=", &arg))
 		return parse_ws_error_highlight(options, arg);
+	else if (!strcmp(arg, "--shift-ita"))
+		options->shift_ita = 1;
 
 	/* misc options */
 	else if (!strcmp(arg, "-z"))
diff --git a/diff.h b/diff.h
index ec76a90..5dd4f9c 100644
--- a/diff.h
+++ b/diff.h
@@ -146,6 +146,7 @@ struct diff_options {
 	int dirstat_permille;
 	int setup;
 	int abbrev;
+	int shift_ita;
 /* white-space error highlighting */
 #define WSEH_NEW 1
 #define WSEH_CONTEXT 2
diff --git a/t/t2203-add-intent.sh b/t/t2203-add-intent.sh
index 8f22c43..c6a4648 100755
--- a/t/t2203-add-intent.sh
+++ b/t/t2203-add-intent.sh
@@ -5,10 +5,24 @@ test_description='Intent to add'
 . ./test-lib.sh
 
 test_expect_success 'intent to add' '
+	test_commit 1 &&
+	git rm 1.t &&
+	echo hello >1.t &&
 	echo hello >file &&
 	echo hello >elif &&
 	git add -N file &&
-	git add elif
+	git add elif &&
+	git add -N 1.t
+'
+
+test_expect_success 'git status' '
+	git status --porcelain | grep -v actual >actual &&
+	cat >expect <<-\EOF &&
+	DA 1.t
+	A  elif
+	 A file
+	EOF
+	test_cmp expect actual
 '
 
 test_expect_success 'check result of "add -N"' '
@@ -43,7 +57,9 @@ test_expect_success 'i-t-a entry is simply ignored' '
 	git add -N nitfol &&
 	git commit -m second &&
 	test $(git ls-tree HEAD -- nitfol | wc -l) = 0 &&
-	test $(git diff --name-only HEAD -- nitfol | wc -l) = 1
+	test $(git diff --name-only HEAD -- nitfol | wc -l) = 1 &&
+	test $(git diff --name-only --shift-ita HEAD -- nitfol | wc -l) = 0 &&
+	test $(git diff --name-only --shift-ita -- nitfol | wc -l) = 1
 '
 
 test_expect_success 'can commit with an unrelated i-t-a entry in index' '
diff --git a/t/t7064-wtstatus-pv2.sh b/t/t7064-wtstatus-pv2.sh
index 3012a4d..e319fa2 100755
--- a/t/t7064-wtstatus-pv2.sh
+++ b/t/t7064-wtstatus-pv2.sh
@@ -246,8 +246,8 @@ test_expect_success 'verify --intent-to-add output' '
 	git add --intent-to-add intent1.add intent2.add &&
 
 	cat >expect <<-EOF &&
-	1 AM N... 000000 100644 100644 $_z40 $EMPTY_BLOB intent1.add
-	1 AM N... 000000 100644 100644 $_z40 $EMPTY_BLOB intent2.add
+	1 .A N... 000000 000000 100644 $_z40 $_z40 intent1.add
+	1 .A N... 000000 000000 100644 $_z40 $_z40 intent2.add
 	EOF
 
 	git status --porcelain=v2 >actual &&
diff --git a/wt-status.c b/wt-status.c
index 9a14658..5f9b1cd 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -437,7 +437,7 @@ static void wt_status_collect_changed_cb(struct diff_queue_struct *q,
 
 		switch (p->status) {
 		case DIFF_STATUS_ADDED:
-			die("BUG: worktree status add???");
+			d->mode_worktree = p->two->mode;
 			break;
 
 		case DIFF_STATUS_DELETED:
@@ -547,6 +547,7 @@ static void wt_status_collect_changes_worktree(struct wt_status *s)
 	setup_revisions(0, NULL, &rev, NULL);
 	rev.diffopt.output_format |= DIFF_FORMAT_CALLBACK;
 	DIFF_OPT_SET(&rev.diffopt, DIRTY_SUBMODULES);
+	rev.diffopt.shift_ita = 1;
 	if (!s->show_untracked_files)
 		DIFF_OPT_SET(&rev.diffopt, IGNORE_UNTRACKED_IN_SUBMODULES);
 	if (s->ignore_submodule_arg) {
@@ -570,6 +571,7 @@ static void wt_status_collect_changes_index(struct wt_status *s)
 	setup_revisions(0, NULL, &rev, &opt);
 
 	DIFF_OPT_SET(&rev.diffopt, OVERRIDE_SUBMODULE_CONFIG);
+	rev.diffopt.shift_ita = 1;
 	if (s->ignore_submodule_arg) {
 		handle_ignore_submodules_arg(&rev.diffopt, s->ignore_submodule_arg);
 	} else {
@@ -605,6 +607,8 @@ static void wt_status_collect_changes_initial(struct wt_status *s)
 
 		if (!ce_path_match(ce, &s->pathspec, NULL))
 			continue;
+		if (ce_intent_to_add(ce))
+			continue;
 		it = string_list_insert(&s->change, ce->name);
 		d = it->util;
 		if (!d) {
@@ -911,6 +915,7 @@ static void wt_longstatus_print_verbose(struct wt_status *s)
 
 	init_revisions(&rev, NULL);
 	DIFF_OPT_SET(&rev.diffopt, ALLOW_TEXTCONV);
+	rev.diffopt.shift_ita = 1;
 
 	memset(&opt, 0, sizeof(opt));
 	opt.def = s->is_initial ? EMPTY_TREE_SHA1_HEX : s->reference;
-- 
2.8.2.524.g6ff3d78