nix-config/modules2/nixvim/edit-alternate/config.nix

{
  flake.modules.nixvim.custom.extraConfigLua = ''
    vim.fn["edit_alternate#rule#add"]("go", function(filename)
      if filename:find "_test%.go$" then
        return filename:gsub("_test%.go$", ".go")
      else
        return filename:gsub("%.go$", "_test.go")
      end
    end)

    vim.fn["edit_alternate#rule#add"]("php", function(filename)
      if filename:find "Test.php$" then
        filename = filename:gsub("Test.php$", ".php")

        if filename:find "tests/src/" then
          -- Drupal tests. Remove the `src/{type}` from the path.
          return filename:gsub("tests/src/(.-)/", "src/")
        else
          return filename:gsub("tests/", "src/")
        end
      else
        filename = filename:gsub(".php$", "Test.php")

        if filename:find "modules/custom" then
          -- Drupal test types.
          local test_types = { "Functional", "FunctionalJavaScript", "Kernel", "Unit" }

          for _, test_type in ipairs(test_types) do
            local filename_with_test_type = filename:gsub("src/", string.format("tests/src/%s/", test_type))

            -- Return the first matching test file that exists.
            if vim.fn.filereadable(filename_with_test_type) == 1 then
              return filename_with_test_type
            end
          end
        end
      end
    end)

    if vim.fn.filereadable "composer.json" == 1 then
      vim.fn["edit_alternate#rule#add"]("json", function(filename)
        if filename:find "composer.json" then
          return (filename:gsub("%.json$", ".lock"))
        end
      end)

      vim.fn["edit_alternate#rule#add"]("lock", function(filename)
        if filename:find "composer.lock" then
          return (filename:gsub("%.lock$", ".json"))
        end
      end)
    end

    if vim.fn.filereadable "fractal.config.js" == 1 then
      vim.fn["edit_alternate#rule#add"]("twig", function(filename)
        return (filename:gsub("%.twig$", ".config.yml"))
      end)

      vim.fn["edit_alternate#rule#add"]("yml", function(filename)
        return (filename:gsub("%.config.yml$", ".twig"))
      end)
    end
  '';
}