Rename detection within in files WAS: [PATCH 2/6] t7408: merge short tests, factor out testing method

[Stefan Beller <sbeller@google.com>]

When moving code around, we usually get large chunks of text. If the contributor
is not 100% trustworthy, we need to review all the code without much intelectual
joy. Essentially the reviewer is just making sure the parts of the text are the
same.

I'd like to propose a new addition to the diff format that makes this use case
easier. The idea is to mark up lines that were just moved around in the file
instead of adding and removing them.

Currently we have 3 characters that
are allowed to start a line within a hunk:
' ' to indicate context
'+' to add a line
'-' to remove a line

I'd propose to add the following characters:
'*' which is the same as '+', but it indicates that the line was moved
    from somewhere else without change.
'X' The same as '-', with the addition that this line was moved to a different
    place without change.

The patch below uses these new '*' and 'X'. Each hunk that makes use of these
additions, is followed other sections, [moved-from, moved-to] that indicate
where the corresponding line is.

There are multiple things to tackle when going for such an addition:
* How to present this to the user (it's covered in this email)
* how to find the renamed lines algorithmically.
  (there are already approaches to that, e.g. https://github.com/stefanbeller/duplo
  which is http://duplo.sourceforge.net/ with no substantial additions)

Any comments welcome,

Thanks,
Stefan

---
 t/t7408-submodule-reference.sh | 50 +++++++++++++++---------------------------
 1 file changed, 15 insertions(+), 29 deletions(-), 6 moved lines

diff --git a/t/t7408-submodule-reference.sh b/t/t7408-submodule-reference.sh
index afcc629..1416cbd 100755
--- a/t/t7408-submodule-reference.sh
+++ b/t/t7408-submodule-reference.sh
@@ -10,6 +10,16 @@ base_dir=$(pwd)

 U=$base_dir/UPLOAD_LOG

+test_alternate_usage()
+{
+	alternates_file=$1
+	working_dir=$2
+	test_line_count = 1 $alternates_file &&
*	echo "0 objects, 0 kilobytes" >expect &&
*	git -C $working_dir count-objects >current &&
*	diff expect current
+}
+
 test_expect_success 'preparing first repository' '
 	test_create_repo A &&
 	(
@@ move-source 42,6 @@ test_expect_success 'that reference gets used with add' '
 test_expect_success 'that reference gets used with add' '
 	(
 		cd super/sub &&
X		echo "0 objects, 0 kilobytes" > expected &&
X		git count-objects > current &&
X		diff expected current
 	)
 '
@@ -42,44 +52,20 @@ test_expect_success 'preparing superproject' '
 	)
 '

-test_expect_success 'submodule add --reference' '
+test_expect_success 'submodule add --reference uses alternates' '
 	(
 		cd super &&
 		git submodule add --reference ../B "file://$base_dir/A" sub &&
 		git commit -m B-super-added
-	)
-'
-
-test_expect_success 'after add: existence of info/alternates' '
-	test_line_count = 1 super/.git/modules/sub/objects/info/alternates
-'
-
-test_expect_success 'that reference gets used with add' '
-	(
-		cd super/sub &&
X		echo "0 objects, 0 kilobytes" > expected &&
X		git count-objects > current &&
X		diff expected current
-	)
-'
-
-test_expect_success 'cloning superproject' '
-	git clone super super-clone
-'
-
@@ move-to 10,6 @@ test_alternate_usage
+	alternates_file=$1
+	working_dir=$2
+	test_line_count = 1 $alternates_file &&
*	echo "0 objects, 0 kilobytes" >expect &&
*	git -C $working_dir count-objects >current &&
*	diff expect current
+}
+
--
2.9.2.572.g9d9644e.dirty