Run luacheck on pushes

.github/workflows/lint.yml

@@ -0,0 +1,18 @@
+name: Lint
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Run luacheck
+        uses: nebularg/actions-luacheck@v1
+        with:
+          annotate: warning
+          args: --no-color

.luacheckrc

@@ -0,0 +1,70 @@
+std = 'lua51'
+
+quiet = 1 -- suppress report output for files without warnings
+
+-- see https://luacheck.readthedocs.io/en/stable/warnings.html#list-of-warnings
+-- and https://luacheck.readthedocs.io/en/stable/cli.html#patterns
+ignore = {
+	'212/self', -- unused argument self
+	'212/event', -- unused argument event
+	'212/unit', -- unused argument unit
+	'212/element', -- unused argument element
+	'312/event', -- unused value of argument event
+	'312/unit', -- unused value of argument unit
+	'431', -- shadowing an upvalue
+	'614', -- trailing whitespace in a comment
+	'631', -- line is too long
+}
+
+exclude_files = {}
+
+globals = {}
+
+read_globals = {
+	table = {fields = {'wipe'}},
+
+	-- SharedXML objects
+	'CopyTable', -- SharedXML/TableUtil.lua
+
+	-- SharedXML functions
+	'GetItemInfoFromHyperlink', -- SharedXML/LinkUtil.lua
+
+	-- namespaces
+	'Enum',
+	'C_Item',
+	'C_TradeSkillUI',
+
+	-- GlobalStrings
+	'TRADE_SKILLS',
+
+	-- enums (old style)
+	'LE_ITEM_QUALITY_UNCOMMON', -- classic only
+	'LE_ITEM_QUALITY_EPIC', -- classic only
+	'LE_EXPANSION_CLASSIC',
+	'LE_EXPANSION_BURNING_CRUSADE',
+	'LE_EXPANSION_WRATH_OF_THE_LICH_KING',
+	'LE_EXPANSION_CATACLYSM',
+	'LE_EXPANSION_MISTS_OF_PANDARIA',
+	'LE_EXPANSION_WARLORDS_OF_DRAENOR',
+	'LE_EXPANSION_LEGION',
+	'LE_EXPANSION_BATTLE_FOR_AZEROTH',
+	'LE_EXPANSION_SHADOWLANDS',
+	'LE_EXPANSION_DRAGONFLIGHT',
+
+	-- API
+	'CreateFrame',
+	'GetBuildInfo',
+	'GetItemCount',
+	'GetItemInfo',
+	'GetProfessionInfo',
+	'GetProfessions',
+	'GetSpellInfo',
+	'IsSpellKnown',
+	'UnitLevel',
+	'GetNumSkillLines', -- classic only
+	'GetSkillLineInfo', -- classic only
+	'ExpandSkillHeader', -- classic only
+
+	-- exposed from other addons
+	'LibStub',
+}