Conditionally load prettier or eslint

[WhyNotHugo]

I've this setup to enable eslint for formatting for javascript projects where its set up, falling back to prettier otherwise.

However, the first source on this sample won't enable prettier for filetypes that eslint cannot handle (in projects where eslint is set up).

E.g.: for an html file on a project with eslint enabled, the first source here won't enable prettier. So I have the second source, which unconditionally enables prettier for all the filetypes that eslint can't handle.

    function()
      -- If the current project has eslint set up, use that, otherwise, use
      -- prettier (which yield good results out of the box and for non-project
      -- files).
      local utils = require("null-ls.utils").make_conditional_utils()

      if utils.root_has_file(".eslintrc.js") then
        return null_ls.builtins.formatting.eslint_d
      else
        return null_ls.builtins.formatting.prettier
      end
    end,
    -- Unconditionally register prettier for all the types that eslint_d can't
    -- handle. The above condition does not register prettier if the project
    -- uses eslint, however we want to register prettier for files that eslint
    -- CANNOT handle.
    null_ls.builtins.formatting.prettier.with({
      filetype = { "css", "scss", "less", "html", "json", "yaml", "markdown", "graphql" },
    }),

This works, but it results in prettier being registered twice in, e.g. vue files, or html files. Is there a cleaner approach to this whole setup?

[jose-elias-alvarez]

Not sure if this is exactly what you're looking for, but if the goal is to avoid registering prettier twice, you could use a condition:

null_ls.builtins.formatting.prettier.with({
    filetype = { "css", "scss", "less", "html", "json", "yaml", "markdown", "graphql" },
    condition = function()
        -- check if prettier is already registered
        return #require("null-ls.sources").get({ name = "prettier" }) == 0
    end,
})

[WhyNotHugo]

Ah, thanks. This syntax using condition is a lot cleaner too.

I've used this to switch eslint diagnostics and code actions to use this:

local function has_eslint_configured()
  local utils = require("null-ls.utils").make_conditional_utils()
  return utils.root_has_file(".eslintrc.js")
end

And then:

    null_ls.builtins.code_actions.eslint_d.with({ condition = has_eslint_configured }),

I realise I can also use the same condition for eslint diagnostics (which would simplify things a lot), but can I then somehow register prettier only if (a) eslint is not registered or (b) eslint does not apply to the current filetype?

[jose-elias-alvarez]

You can actually simplify even further, since condition is called with a utils object:

local function has_eslint_configured(utils)
    return utils.root_has_file(".eslintrc.js")
end

It's technically possible to check those conditions, but I don't know if it'll be 100% reliable. condition is checked when you first enter a named buffer, so if that buffer's filetype doesn't fit the condition, things might go wrong, but otherwise this will work:

local eslint_filetypes = null_ls.builtins.formatting.eslint.filetypes

local prettier = null_ls.builtins.formatting.prettier.with({
    condition = function()
        return #null_ls.get_source({ name = "eslint", method = null_ls.methods.FORMATTING }) == 0
            or not vim.tbl_contains(eslint_filetypes, vim.bo.filetypes)
    end,
})

You might be better off using different built-ins, modifying their filetypes individually, and registering them conditionally based on whether the other has been registered.

[WhyNotHugo]

You can actually simplify even further, since condition is called with a utils object:

This is great, very handy! Thanks for all the pointers.

[WhyNotHugo]

Alright, so I finally got to the simplest form, which also doesn't require mangling filetyes 😌

-- Helper to conditionally register eslint handlers only if eslint is
-- configured. If eslint is not configured for a project, it just fails.
local function has_eslint_configured(utils)
  return utils.root_has_file(".eslintrc.js")
end

null_ls.setup({
  sources = {
    null_ls.builtins.code_actions.eslint_d.with({ condition = has_eslint_configured }),
    null_ls.builtins.diagnostics.eslint_d.with({ condition = has_eslint_configured }),
    null_ls.builtins.formatting.eslint_d.with({ condition = has_eslint_configured }),
    null_ls.builtins.formatting.prettier.with({
      -- Only register prettier if eslint_d is not running as a formatter. This
      -- can happen if it's not configured for this project, or if it can't
      -- handle the current filetype.
      condition = function()
        return #null_ls.get_source({ name = "eslint_d", method = null_ls.methods.FORMATTING }) == 0
      end,
    }),

Thanks again for all the help!

[justgage]

Nice! This is awesome! Fixed all my issues with how my setup was trying to work with the default setup.

[piersolenski]

I've tried using the different configurations on this discussion, but I can't seem to handle the use case of having eslint_d handle my "javascript", "javascriptreact", "typescript", "typescriptreact" and "vue" files, but keep using prettierd for my "json" files - which eslint doesn't support according to the builtins. Any idea how I can extend this configuration to handle that?

[WhyNotHugo]

The above is most of what I needed for that. My full config is here, hope it helps.

[winkee01]

thanks for the summarized config, I applied it, but seems it does not auto format my file on saving.