round-robin-bisect.sh: Handle another edge case

... in bisection of merge history.  We can detect first_bad commit
with a good parent that is outside of bisection range.  E.g.,

 BAD
  | \
BASE \
  |  FIRST BAD
  | /
PARENT

In this case PARENT is the last good revision, but falls outside
of bisection range.

Change-Id: I4b88b6c7a245f390705df70943cccd70964fd7f6

1 files changed, 17 insertions, 4 deletions

diff --git a/round-robin-bisect.sh b/round-robin-bisect.sh
index a6a8511f..96619b99 100755
--- a/round-robin-bisect.sh
+++ b/round-robin-bisect.sh
@@ -407,10 +407,6 @@ if [ x"$first_bad" != x"" ]; then
     last_good=""
     bad_last_good=""
     for sha1 in $(git rev-parse $first_bad^@); do
-	# Ignore commits outside of bisection range.
-	if ! grep -q "^$sha1\$" $commits_in_range; then
-	    continue
-	fi
 	# It seems that git-bisect assumes parent commit as "good" on
 	# the basis of one of its children being "good".  Therefore we
 	# can have a situation when we have parent P with children C1 and C2,
@@ -419,6 +415,23 @@ if [ x"$first_bad" != x"" ]; then
 	# and it knows CB is "bad", so git-bisect returns C1 as the first bad
 	# commit.
 	# To simplify investigations we explicitly test parent of $first_bad.
+
+	# Ignore commits outside of bisection range, but make an exception
+	# for commits that weren't tested due to their child tested good.
+	# This happens in projects that actively use merges, e.g., linux.
+	if ! grep -q "^$sha1\$" $commits_in_range; then
+	    child_tested_good=false
+	    for tested_good in $(print_tested_revs good); do
+		if git merge-base --is-ancestor $sha1 $tested_good; then
+		    child_tested_good=true
+		    break
+		fi
+	    done
+	    if ! $child_tested_good; then
+		continue
+	    fi
+	fi
+
 	echo "Testing first_bad's parent $sha1 (hoping for success)"
 	git checkout --detach "$sha1"
 	$artifacts/test.sh &