Introduce early Lua formatting library inspired by Rust

plugin/fmt/init.lua

@@ -0,0 +1,54 @@
+local function debugOutputBuffer()
+	local buffer = {}
+	local indentLevel = 0
+	local indentation = ""
+
+	function buffer:push(template, ...)
+		local value = string.format(template, ...)
+
+		if #indentation > 0 then
+			value = indentation .. value:gsub("\n", "\n" .. indentation)
+		end
+
+		table.insert(self, value)
+	end
+
+	function buffer:indent()
+		indentLevel = indentLevel + 1
+		indentation = string.rep("    ", indentLevel)
+	end
+
+	function buffer:unindent()
+		indentLevel = math.max(0, indentLevel - 1)
+		indentation = string.rep("    ", indentLevel)
+	end
+
+	function buffer:finish()
+		return table.concat(self, "\n")
+	end
+
+	return buffer
+end
+
+local function debugInner(value)
+	local valueType = typeof(value)
+
+	if valueType == "string" then
+		return string.format("%q", value)
+	elseif valueType == "number" then
+		return tostring(value)
+	elseif valueType == "table" then
+		local debugImpl = getmetatable(value).__fmtDebug
+
+		if debugImpl ~= nil then
+			return debugImpl()
+		else
+			-- TODO: Nicer default debug implementation?
+			return tostring(value)
+		end
+	end
+end
+
+return {
+	debugOutputBuffer = debugOutputBuffer,
+}