tests: shellcheck: add shellcheck

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

tests/patch/shellcheck/info.json

@@ -0,0 +1,3 @@
+{
+  "run": ["shellcheck.sh"]
+}

tests/patch/shellcheck/shellcheck.sh

@@ -0,0 +1,78 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+HEAD=$(git rev-parse HEAD)
+tmpfile_o=$(mktemp)
+tmpfile_n=$(mktemp)
+rc=0
+
+pr() {
+    echo " ====== $@ ======" | tee -a /dev/stderr
+}
+
+# If it doesn't touch .sh files, don't bother. Ignore created and deleted.
+if ! git show --diff-filter=M --pretty="" --name-only HEAD | grep -q -E "\.sh$"
+then
+    echo "No shell scripts touched, skip" >&$DESC_FD
+    exit 0
+fi
+
+echo "Redirect to $tmpfile_o and $tmpfile_n"
+
+echo "Tree base:"
+git log -1 --pretty='%h ("%s")' HEAD~
+echo "Now at:"
+git log -1 --pretty='%h ("%s")' HEAD
+
+pr "Checking before the patch"
+git checkout -q HEAD~
+
+for f in $(git show --diff-filter=M --pretty="" --name-only HEAD | grep -E "\.sh$"); do
+    (
+	echo "Checking $f"
+	echo
+
+	cd $(dirname $f)
+	shellcheck -x $(basename $f) | tee -a $tmpfile_o
+	echo
+    )
+done
+
+incumbent=$(grep -i -c "(error)" $tmpfile_o)
+incumbent_w=$(grep -i -c "SC[0-9]* (" $tmpfile_o)
+
+pr "Building the tree with the patch"
+git checkout -q $HEAD
+
+for f in $(git show --diff-filter=AM --pretty="" --name-only HEAD | grep -E "\.sh$"); do
+    (
+	echo "Checking $f"
+	echo
+
+	cd $(dirname $f)
+	shellcheck -x $(basename $f) | tee -a $tmpfile_n
+	echo
+    )
+done
+
+current=$(grep -i -c "(error)" $tmpfile_n)
+current_w=$(grep -i -c "SC[0-9]* (" $tmpfile_n)
+
+echo "Errors before: $incumbent (+warn: $incumbent_w) this patch: $current (+warn: $current_w)" >&$DESC_FD
+
+if [ $current -gt $incumbent ]; then
+  echo "New errors added" 1>&2
+  diff -U 0 $tmpfile_o $tmpfile_n 1>&2
+
+  rc=1
+fi
+
+if [ $current_w -gt $incumbent_w ]; then
+    echo "New warnings added" 1>&2
+
+    rc=250
+fi
+
+rm "$tmpfile_o" "$tmpfile_n"
+
+exit $rc