A one-size-fits-all fmt plugin for Micro text-editor

fmt.lua

VERSION = "1.0.0"

-- Table (of tables) for lookup (keep alphabetical order plz).
-- Reported filetype (by Micro) on the left, command & args on the right.
fmt_table = {
  ["fish"] = {"fishfmt", "-w"},
  ["go"] = {"gofmt", "-s -w"},
  ["rust"] = {"rustfmt", nil}, -- no args, overwrite is default
  ["shell"] = {"shfmt", "-s -w"}
}

-- Declares the table & options to enable/disable formatter(s)
-- Avoids manually defining commands twice by reading the table
for i, value in pairs(fmt_table) do
  -- i and value[2] aren't needed here. Maybe optimize this?
  
  -- An empty table element would return nil
  if value[1] ~= nil then
    -- value[2] would return args, which we don't need here. We want the cmd string.
    if GetOption(value[1]) == nil then
      -- Disabled by default, require user to enable for safety
      AddOption(value[1], false)
    end
  end
end

function run_fmt()
  -- Prevent infinite loop of onSave()
  CurView():Save(false)
      
  local file_type = CurView().Buf:FileType()
  -- The literal filetype name (`rust`, `shell`, etc.) is the table's key
  -- [1] is the cmd, [2] is args
  local target_fmt = fmt_table[file_type]
  
  -- Only do anything if the filetype has is a supported formatter
  if target_fmt ~= nil then
    -- Only do anything if the specified formatter is enabled
    if GetOption(target_fmt[1]) then

      -- Load in the 'base' command (ex: `rustfmt`, `gofmt`, etc.)
      local cmd = target_fmt[1]
      -- Check for args
      if target_fmt[2] ~= nil then
        -- Add a space between cmd & args
        cmd = cmd .. " " .. target_fmt[2]
      end
      -- Add a space between the cmd & path
      cmd = cmd .. " "
      
      -- Actually run the format command
      local handle = io.popen(cmd .. CurView().Buf.Path)
      local result = handle:read("*a")
      handle:close()
      -- Reload
      CurView():ReOpen()
    end
  end
end

function onSave(view)
  run_fmt()
end

-- User command
MakeCommand("fmt", "fmt.run_fmt", 0)

For anyone reading, this idea got expanded into the fmt plugin, so if you want something similar then use that instead.