bisect: Log possibly bad, skipped commits at bisection end

If the bisection completes with only skipped commits left to as possible
first bad commit, output the list of possible first bad commits to human
readers of the bisection log.

Signed-off-by: Torstein Hegge <hegge@resisty.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-bisect.sh

@@ -317,6 +317,16 @@ bisect_next() {
 		bad_commit=$(git show-branch $bad_rev)
 		echo "# first bad commit: $bad_commit" >>"$GIT_DIR/BISECT_LOG"
 		exit 0
+	elif test $res -eq 2
+	then
+		echo "# only skipped commits left to test" >>"$GIT_DIR/BISECT_LOG"
+		good_revs=$(git for-each-ref --format="--not %(objectname)" "refs/bisect/good-*")
+		for skipped in $(git rev-list refs/bisect/bad $good_revs)
+		do
+			skipped_commit=$(git show-branch $skipped)
+			echo "# possible first bad commit: $skipped_commit" >>"$GIT_DIR/BISECT_LOG"
+		done
+		exit $res
 	fi
 
 	# Check for an error in the bisection process

t/t6030-bisect-porcelain.sh

@@ -759,4 +759,24 @@ test_expect_success 'bisect log: successfull result' '
 	git bisect reset
 '
 
+cat > expected.bisect-skip-log <<EOF
+# bad: [32a594a3fdac2d57cf6d02987e30eec68511498c] Add <4: Ciao for now> into <hello>.
+# good: [7b7f204a749c3125d5224ed61ea2ae1187ad046f] Add <2: A new day for git> into <hello>.
+git bisect start '32a594a3fdac2d57cf6d02987e30eec68511498c' '7b7f204a749c3125d5224ed61ea2ae1187ad046f'
+# skip: [3de952f2416b6084f557ec417709eac740c6818c] Add <3: Another new day for git> into <hello>.
+git bisect skip 3de952f2416b6084f557ec417709eac740c6818c
+# only skipped commits left to test
+# possible first bad commit: [32a594a3fdac2d57cf6d02987e30eec68511498c] Add <4: Ciao for now> into <hello>.
+# possible first bad commit: [3de952f2416b6084f557ec417709eac740c6818c] Add <3: Another new day for git> into <hello>.
+EOF
+
+test_expect_success 'bisect log: only skip commits left' '
+	git bisect reset &&
+	git bisect start $HASH4 $HASH2 &&
+	test_must_fail git bisect skip &&
+	git bisect log >bisect-skip-log.txt &&
+	test_cmp expected.bisect-skip-log bisect-skip-log.txt &&
+	git bisect reset
+'
+
 test_done