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Lua code formatter
Updated 2026-10-28 Created 2016 License LGPL3 Code size < 150 K 💾 reformat_lua	Reformats Lua 5.5 source code to fit right margin. Strips comments.	Input Output .lua .lua

Historical note

Initial version was relased in 2018. In 2026 I returned to this project and did following chnages:

• No comments

  Comments are not considered part of code.

• No Luarocks

  Now tool is self-sufficient file.

• Changed scope

  Tool is positioned as machine-level code viewer.

  So no matter how bad and dirty is source code, it will reduce it to some canonic form.

  Back side is that it will make code that you like look worse.

Feel free to tweak formatting routines to your taste but keep in mind that visual niceness is not in flight plan.

Shipment

Repository contains

• Compiled code in deploy/
• Sample input/output in test/
• Complete source code in src/
• Rebuild script and tools in builder/

Requirements

• Linux
• Lua 5.5 (5.4, 5.3).

Usage

From command-line

$ lua reformat.lua
Reformat Lua 5.5 code.

Usage:   f_in   f_out
       ┬      ┬       ┬
       │      │       │
       └── [options] ─┘

<options>:

  --indent=<str>        Use given string as indent chunk.
  --right-margin=<int>  Right margin.

-- Martin, 2026-10

From Lua interpreter

Suppose you have a string with Lua code and wish to get another string with formatted code.

do
  local lua_code_str = 'do return end' -- < fill it

  require('workshop.base')
  local reformat = request('!.lua.code.reformat')

  return reformat(lua_code_str)
end

Passing formatting parameters

You may override default parameters by passing a table with new values of changed parameters:

reformat(
  lua_code_str,
  {
    indent_chunk = '  ',
    right_margin = 72,
  }
)

Parameter	Default	Description
indent_chunk		String used for building one indent.
right_margin	72	Maximum line length with indent.

Changing formatting logic

First, general workflow of this formatter:

1. Load .lua file as string.
2. Parse that string to tree in table.
3. Change nodes of that tree to make it easier to handle in formatting routines.
4. Run formatting routines for all nodes in tree. Formatting routines output to virtual printer.
5. Write contents of virtual printer to file.

We are at point 4. Start tinkering from something simple but usable as "repeat" block handling: workshop/concepts/lua/formatter/handlers/statements/blocks/repeat_block.lua

See also

• workshop -- My personal Lua framework
• My other projects