Merge #12708: Make verify-commits.sh test that merges are clean

577f111 Make verify-commits.sh test that merges are clean (Pieter Wuille)

Pull request description:

  Unsure if we want this.

  This modifies verify-commits.sh to redo all merges along the leftmost commit branch (which includes all PR merges), and verify whether they match the merge commit's trees.

  The benefit is that it will detect a case where one of the maintainers merges a PR, but makes an unrelated change inside the merge commit. This on itself is not very strong, as unrelated changes can also be included in the merged branch itself - but perhaps the merge commit is not something that people are otherwise likely to look at.

  Fixes #8089

Tree-SHA512: 2c020f5ac3f771ac775aa726832916bb8e03a311b2745d7a9825047239bd0660d838f086f3456f2bb05cea14c1529f74436b8cdd74cc94b70e40b4617309f62c

Author: laanwj

contrib/verify-commits/verify-commits.sh

@@ -35,6 +35,8 @@ NO_SHA1=1
 PREV_COMMIT=""
 INITIAL_COMMIT="${CURRENT_COMMIT}"
 
+BRANCH="$(git rev-parse --abbrev-ref HEAD)"
+
 while true; do
 	if [ "$CURRENT_COMMIT" = $VERIFIED_ROOT ]; then
 		echo "There is a valid path from \"$INITIAL_COMMIT\" to $VERIFIED_ROOT where all commits are signed!"
@@ -123,9 +125,29 @@ while true; do
 	fi
 
 	PARENTS=$(git show -s --format=format:%P "$CURRENT_COMMIT")
-	for PARENT in $PARENTS; do
-		PREV_COMMIT="$CURRENT_COMMIT"
-		CURRENT_COMMIT="$PARENT"
-		break
-	done
+	PARENT1=${PARENTS%% *}
+	PARENT2=""
+	if [ "x$PARENT1" != "x$PARENTS" ]; then
+		PARENTX=${PARENTS#* }
+		PARENT2=${PARENTX%% *}
+		if [ "x$PARENT2" != "x$PARENTX" ]; then
+			echo "Commit $CURRENT_COMMIT is an octopus merge" > /dev/stderr
+			exit 1
+		fi
+	fi
+	if [ "x$PARENT2" != "x" ]; then
+		CURRENT_TREE="$(git show --format="%T" "$CURRENT_COMMIT")"
+		git checkout --force --quiet "$PARENT1"
+		git merge --no-ff --quiet "$PARENT2" >/dev/null
+		RECREATED_TREE="$(git show --format="%T" HEAD)"
+		if [ "$CURRENT_TREE" != "$RECREATED_TREE" ]; then
+			echo "Merge commit $CURRENT_COMMIT is not clean" > /dev/stderr
+			git diff "$CURRENT_COMMIT"
+			git checkout --force --quiet "$BRANCH"
+			exit 1
+		fi
+		git checkout --force --quiet "$BRANCH"
+	fi
+	PREV_COMMIT="$CURRENT_COMMIT"
+	CURRENT_COMMIT="$PARENT1"
 done