try luacheck

.github/workflows/luacheck.yml

@@ -0,0 +1,10 @@
+name: Luacheck
+on: [push, pull_request]
+jobs:
+  sile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Luacheck linter
+        uses: nebularg/actions-luacheck@v1

.luacheckrc

@@ -0,0 +1,15 @@
+max_line_length=140
+-- show the warning/error codes as well
+codes=true
+-- skip showing files with no issues
+quiet=1
+-- checks related to undefined variable usage
+-- there can be warnings because luacheck is unaware of Wesnoth's
+-- lua environment and has no way to check which have been loaded
+globals={"wesnoth","wml","gui","filesystem","unit_test","stringx","mathx","ai"}
+-- allow_defined=true
+-- allow_defined_top=true
+-- skip showing unused variables
+-- unused=false
+-- skip showing warnings about shadowing upvalues
+-- ignore={"431"}