[PATCH v5 2/2] difftool.c: learn a new way start at specified file

["ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com>]

From: ZheNing Hu <adlternative@gmail.com>

`git difftool` only allow us to select file to view in turn.
If there is a commit with many files and we exit in the search,
We will have to traverse list again to get the file diff which
we want to see. Therefore, here is a new method: user can use
`git difftool --rotate-to=<filename>` or `git difftool --skip-to=<filename>`
to start viewing from the specified file, This will improve the
user experience.

`git difftool --rotate-to=<file>` or `git difftool --skip-to=<filename>`
will pass the path to `diffcore-rotate`, and diff-core will
adjust the order of files, make the specified file sorted to
the first.`git difftool --rotate-to=<file>` will move files before
the  specified path to the last output, and
`git difftool --skip-to=<filename>`  will ignore these files output.
It is an error when there is no patch for specified file is shown.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
 Documentation/diff-options.txt |  2 +-
 Documentation/git-difftool.txt | 10 ++++++++++
 t/t7800-difftool.sh            | 30 ++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 7c5b3cf42bcc..aa2b5c11f20b 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -701,7 +701,7 @@ components matches the pattern.  For example, the pattern "`foo*bar`"
 matches "`fooasdfbar`" and "`foo/bar/baz/asdf`" but not "`foobarx`".
 
 --skip-to=<file>::
---rotate-to=<file::
+--rotate-to=<file>::
 	Discard the files before the named <file> from the output
 	(i.e. 'skip to'), or move them to the end of the output
 	(i.e. 'rotate to').  These were invented primarily for use
diff --git a/Documentation/git-difftool.txt b/Documentation/git-difftool.txt
index 484c485fd06c..c64dff69c976 100644
--- a/Documentation/git-difftool.txt
+++ b/Documentation/git-difftool.txt
@@ -34,6 +34,16 @@ OPTIONS
 	This is the default behaviour; the option is provided to
 	override any configuration settings.
 
+--rotate-to=<file>::
+	Internally call `git diff --rotate-to=<file>`,
+	show the change in the specified path first.
+	Files before the specified path will be moved to the last output.
+
+--skip-to=<file>::
+	Internally call `git diff --skip-to=<file>`,
+	skip the output to the specified path.
+	Files before the specified path will not output.
+
 -t <tool>::
 --tool=<tool>::
 	Use the diff tool specified by <tool>.  Valid values include
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 9192c141ffc6..112b798b1c23 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -762,4 +762,34 @@ test_expect_success 'difftool --gui, --tool and --extcmd are mutually exclusive'
 	test_must_fail git difftool --gui --tool=test-tool --extcmd=cat
 '
 
+test_expect_success 'difftool --rotate-to' '
+	difftool_test_setup &&
+	test_when_finished git reset --hard &&
+	echo 1 >1 &&
+	echo 2 >2 &&
+	echo 4 >4 &&
+	git add 1 2 4 &&
+	git commit -a -m "124" &&
+	git difftool --no-prompt --extcmd=cat --rotate-to="2" HEAD^ >output&&
+	cat >expect <<-\EOF &&
+	2
+	4
+	1
+	EOF
+	test_cmp output expect &&
+	test_must_fail git difftool --no-prompt --extcmd=cat --rotate-to="3" HEAD^
+'
+
+test_expect_success 'difftool --skip-to' '
+	difftool_test_setup &&
+	test_when_finished git reset --hard &&
+	git difftool --no-prompt --extcmd=cat --skip-to="2" HEAD^ >output &&
+	cat >expect <<-\EOF &&
+	2
+	4
+	EOF
+	test_cmp output expect &&
+	test_must_fail git difftool --no-prompt --extcmd=cat --skip-to="3" HEAD^
+'
+
 test_done
-- 
gitgitgadget