plugin: Add API interface for strongly typing responses

plugin/src/strict.lua

@@ -0,0 +1,24 @@
+local function strictInner(name, target)
+	assert(type(name) == "string", "Argument #1 to `strict` must be a string or the table to modify")
+	assert(type(target) == "table", "Argument #2 to `strict` must be nil or the table to modify")
+
+	setmetatable(target, {
+		__index = function(_, key)
+			error(("%q is not a valid member of strict table %q"):format(tostring(key), name), 2)
+		end,
+
+		__newindex = function()
+			error(("Strict table %q is read-only"):format(name), 2)
+		end,
+	})
+
+	return target
+end
+
+return function(nameOrTarget, target)
+	if type(nameOrTarget) == "string" then
+		return strictInner(nameOrTarget, target)
+	else
+		return strictInner("<unnamed table>", target)
+	end
+end