New --dirstat=lines mode, doing dirstat analysis based on diffstat

This patch adds an alternative implementation of show_dirstat(), called
show_dirstat_by_line(), which uses the more expensive diffstat analysis
(as opposed to show_dirstat()'s own (relatively inexpensive) analysis)
to derive the numbers from which the --dirstat output is computed.

The alternative implementation is controlled by the new "lines" parameter
to the --dirstat option (or the diff.dirstat config variable).

For binary files, the diffstat analysis counts bytes instead of lines,
so to prevent binary files from dominating the dirstat results, the
byte counts for binary files are divided by 64 before being compared to
their textual/line-based counterparts. This is a stupid and ugly - but
very cheap - heuristic.

In linux-2.6.git, running the three different --dirstat modes:

  time git diff v2.6.20..v2.6.30 --dirstat=changes > /dev/null
vs.
  time git diff v2.6.20..v2.6.30 --dirstat=lines > /dev/null
vs.
  time git diff v2.6.20..v2.6.30 --dirstat=files > /dev/null

yields the following average runtimes on my machine:

 - "changes" (default): ~6.0 s
 - "lines":             ~9.6 s
 - "files":             ~0.1 s

So, as expected, there's a considerable performance hit (~60%) by going
through the full diffstat analysis as compared to the default "changes"
analysis (obviously, "files" is much faster than both). As such, the
"lines" mode is probably only useful if you really need the --dirstat
numbers to be consistent with the numbers returned from the other
--*stat options.

The patch also includes documentation and tests for the new dirstat mode.

Improved-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/t/t4047-diff-dirstat.sh b/t/t4047-diff-dirstat.sh
index 4b25e10030..b8ad92a354 100755
--- a/t/t4047-diff-dirstat.sh
+++ b/t/t4047-diff-dirstat.sh
@@ -839,4 +839,104 @@ test_expect_success '--dirstat=files,cumulative,27.09' '
 	test_cmp expect_diff_dirstat_CC actual_diff_dirstat_CC
 '
 
+cat <<EOF >expect_diff_dirstat
+  10.6% dst/copy/changed/
+  10.6% dst/copy/rearranged/
+  10.6% dst/copy/unchanged/
+  10.6% dst/move/changed/
+  10.6% dst/move/rearranged/
+  10.6% dst/move/unchanged/
+  10.6% src/move/changed/
+  10.6% src/move/rearranged/
+  10.6% src/move/unchanged/
+EOF
+
+cat <<EOF >expect_diff_dirstat_M
+   5.2% changed/
+  26.3% dst/copy/changed/
+  26.3% dst/copy/rearranged/
+  26.3% dst/copy/unchanged/
+   5.2% dst/move/changed/
+   5.2% dst/move/rearranged/
+   5.2% rearranged/
+EOF
+
+cat <<EOF >expect_diff_dirstat_CC
+  16.6% changed/
+  16.6% dst/copy/changed/
+  16.6% dst/copy/rearranged/
+  16.6% dst/move/changed/
+  16.6% dst/move/rearranged/
+  16.6% rearranged/
+EOF
+
+test_expect_success '--dirstat=lines' '
+	git diff --dirstat=lines HEAD^..HEAD >actual_diff_dirstat &&
+	test_cmp expect_diff_dirstat actual_diff_dirstat &&
+	git diff --dirstat=lines -M HEAD^..HEAD >actual_diff_dirstat_M &&
+	test_cmp expect_diff_dirstat_M actual_diff_dirstat_M &&
+	git diff --dirstat=lines -C -C HEAD^..HEAD >actual_diff_dirstat_CC &&
+	test_cmp expect_diff_dirstat_CC actual_diff_dirstat_CC
+'
+
+test_expect_success 'diff.dirstat=lines' '
+	git -c diff.dirstat=lines diff --dirstat HEAD^..HEAD >actual_diff_dirstat &&
+	test_cmp expect_diff_dirstat actual_diff_dirstat &&
+	git -c diff.dirstat=lines diff --dirstat -M HEAD^..HEAD >actual_diff_dirstat_M &&
+	test_cmp expect_diff_dirstat_M actual_diff_dirstat_M &&
+	git -c diff.dirstat=lines diff --dirstat -C -C HEAD^..HEAD >actual_diff_dirstat_CC &&
+	test_cmp expect_diff_dirstat_CC actual_diff_dirstat_CC
+'
+
+cat <<EOF >expect_diff_dirstat
+   2.1% changed/
+  10.6% dst/copy/changed/
+  10.6% dst/copy/rearranged/
+  10.6% dst/copy/unchanged/
+  10.6% dst/move/changed/
+  10.6% dst/move/rearranged/
+  10.6% dst/move/unchanged/
+   2.1% rearranged/
+  10.6% src/move/changed/
+  10.6% src/move/rearranged/
+  10.6% src/move/unchanged/
+EOF
+
+cat <<EOF >expect_diff_dirstat_M
+   5.2% changed/
+  26.3% dst/copy/changed/
+  26.3% dst/copy/rearranged/
+  26.3% dst/copy/unchanged/
+   5.2% dst/move/changed/
+   5.2% dst/move/rearranged/
+   5.2% rearranged/
+EOF
+
+cat <<EOF >expect_diff_dirstat_CC
+  16.6% changed/
+  16.6% dst/copy/changed/
+  16.6% dst/copy/rearranged/
+  16.6% dst/move/changed/
+  16.6% dst/move/rearranged/
+  16.6% rearranged/
+EOF
+
+test_expect_success '--dirstat=lines,0' '
+	git diff --dirstat=lines,0 HEAD^..HEAD >actual_diff_dirstat &&
+	test_cmp expect_diff_dirstat actual_diff_dirstat &&
+	git diff --dirstat=lines,0 -M HEAD^..HEAD >actual_diff_dirstat_M &&
+	test_cmp expect_diff_dirstat_M actual_diff_dirstat_M &&
+	git diff --dirstat=lines,0 -C -C HEAD^..HEAD >actual_diff_dirstat_CC &&
+	test_cmp expect_diff_dirstat_CC actual_diff_dirstat_CC
+'
+
+test_expect_success 'diff.dirstat=0,lines' '
+	git -c diff.dirstat=0,lines diff --dirstat HEAD^..HEAD >actual_diff_dirstat &&
+	test_cmp expect_diff_dirstat actual_diff_dirstat &&
+	git -c diff.dirstat=0,lines diff --dirstat -M HEAD^..HEAD >actual_diff_dirstat_M &&
+	test_cmp expect_diff_dirstat_M actual_diff_dirstat_M &&
+	git -c diff.dirstat=0,lines diff --dirstat -C -C HEAD^..HEAD >actual_diff_dirstat_CC &&
+	test_cmp expect_diff_dirstat_CC actual_diff_dirstat_CC
+'
+
 test_done