Subject: [PATCH 2/2] line-log: show all line ranges touched by the same diff range

From: SZEDER Gábor <[email-masked]>
Date: Mon, 18 Aug 2025 13:13:10 +0200

When line-level log is invoked with more than one disjoint line range
in the same file, and one of the commits happens to change that file
such that one diff range modifies more than one line range, then
changes to all modified line ranges should be shown, but only the
changes in the first modified line range are:

  $ git log --oneline -p
  80ca903 (HEAD -> master) Initial
  diff --git a/file b/file
  new file mode 100644
  index 0000000..00935f1
  --- /dev/null
  +++ b/file
  @@ -0,0 +1,10 @@
  +Line 1
  +Line 2
  +Line 3
  +Line 4
  +Line 5
  +Line 6
  +Line 7
  +Line 8
  +Line 9
  +Line 10
  $ git log --oneline -L1,2:file -L4,5:file -L7,8:file
  80ca903 (HEAD -> master) Initial

  diff --git a/file b/file
  --- /dev/null
  +++ b/file
  @@ -0,0 +1,2 @@
  +Line 1
  +Line 2

The line-log-specific diff printer is already clever enough to handle
the case when one line range covers multiple diff ranges, but the
possibility of one diff range touching multiple disjoint line ranges
was apparently overlooked.

Add the necessary condition to dump_diff_hacky_one() to handle this case
as well, and show all modified line ranges:

  $ git log --oneline -L1,2:file -L4,5:file -L7,8:file
  0f9a5b4 (HEAD -> master) Initial

  diff --git a/file b/file
  --- /dev/null
  +++ b/file
  @@ -0,0 +1,2 @@
  +Line 1
  +Line 2
  @@ -0,0 +4,2 @@
  +Line 4
  +Line 5
  @@ -0,0 +7,2 @@
  +Line 7
  +Line 8

This bug was already present in the initial line-log implementation
added in 2da1d1f6f (Implement line-history search (git log -L),
2013-03-28).  Interestingly, that commit already contained a canned
test case covering a similar scenario:

  "-L '/long f/',/^}/:a.c -L /main/,/^}/:a.c simple"

This test case looks for two line ranges in the same file, and both
trace back disjointly to the test repository's inital commit,
therefore changes to both line ranges should have been shown for the
initial commit, but only changes for the first line range are shown.
So this test case should have failed from the very beginning, but it
never did, because, unfortunately, the canned expected result is
incorrect, as it doesn't include changes for the second line range.

A similar test with a similarly incorrect canned expected result was
added later in 209618860c (log -L: fix overlapping input ranges,
2013-04-05).

Correct these two canned expected results to contain the changes for
the second line range for the initial commit as well.

Signed-off-by: SZEDER Gábor <[email-masked]>
---
 line-log.c                       | 9 +++++++++
 t/t4211/sha1/expect.multiple     | 6 ++++++
 t/t4211/sha1/expect.two-ranges   | 6 ++++++
 t/t4211/sha256/expect.multiple   | 6 ++++++
 t/t4211/sha256/expect.two-ranges | 6 ++++++
 5 files changed, 33 insertions(+)

diff --git a/line-log.c b/line-log.c
index 9cb8ea1484..9b75b4ac39 100644
--- a/line-log.c
+++ b/line-log.c
@@ -939,6 +939,15 @@ static void dump_diff_hacky_one(struct rev_info *rev, struct line_log_data *rang
 		long t_cur = t_start;
 		unsigned int j_last;
 
+		/*
+		 * If a diff range touches multiple line ranges, then all
+		 * those line ranges should be shown, so take a step back if
+		 * the current line range is still in the previous diff range
+		 * (even if only partially).
+		 */
+		if (j > 0 && diff->target.ranges[j-1].end > t_start)
+			j--;
+
 		while (j < diff->target.nr && diff->target.ranges[j].end < t_start)
 			j++;
 		if (j == diff->target.nr || diff->target.ranges[j].start >= t_end)
diff --git a/t/t4211/sha1/expect.multiple b/t/t4211/sha1/expect.multiple
index 76ad5b598c..1eee8a7801 100644
--- a/t/t4211/sha1/expect.multiple
+++ b/t/t4211/sha1/expect.multiple
@@ -102,3 +102,9 @@ diff --git a/a.c b/a.c
 +		s++;
 +	}
 +}
+@@ -0,0 +16,5 @@
++int main ()
++{
++	printf("%d\n", f(15));
++	return 0;
++}
diff --git a/t/t4211/sha1/expect.two-ranges b/t/t4211/sha1/expect.two-ranges
index 6109aa0dce..c5164f3be3 100644
--- a/t/t4211/sha1/expect.two-ranges
+++ b/t/t4211/sha1/expect.two-ranges
@@ -100,3 +100,9 @@ diff --git a/a.c b/a.c
 +		s++;
 +	}
 +}
+@@ -0,0 +16,5 @@
++int main ()
++{
++	printf("%d\n", f(15));
++	return 0;
++}
diff --git a/t/t4211/sha256/expect.multiple b/t/t4211/sha256/expect.multiple
index ca00409b9a..dbd987b74a 100644
--- a/t/t4211/sha256/expect.multiple
+++ b/t/t4211/sha256/expect.multiple
@@ -102,3 +102,9 @@ diff --git a/a.c b/a.c
 +		s++;
 +	}
 +}
+@@ -0,0 +16,5 @@
++int main ()
++{
++	printf("%d\n", f(15));
++	return 0;
++}
diff --git a/t/t4211/sha256/expect.two-ranges b/t/t4211/sha256/expect.two-ranges
index af57c8b997..6a94d3b9cb 100644
--- a/t/t4211/sha256/expect.two-ranges
+++ b/t/t4211/sha256/expect.two-ranges
@@ -100,3 +100,9 @@ diff --git a/a.c b/a.c
 +		s++;
 +	}
 +}
+@@ -0,0 +16,5 @@
++int main ()
++{
++	printf("%d\n", f(15));
++	return 0;
++}
-- 
2.51.0.rc2.346.g6515629ae9