Nu-Lint

Linter for the innovative Nu shell.

Learning to use a new shell is a radical change that can use some assistance. This project is aimed at helping new and intermediate users of the Nu shell. Nu shell has a lot of useful features not found in other scripting languages. This linter will give you hints to use all of them and even offer automatic fixes.

All rules are optional and can be disabled with a configuration file. The rule definitions are designed to be compatible with:

• The standard Nu parser nu-check.
• The standard Nu formatter topiary-nushell.

Example

The rule turn_positional_into_stream_input recommends to use pipelines instead of positional arguments:

def filter-positive [numbers] { 
    $numbers | where $it > 0 
}

def filter-positive [] { 
    where $it > 0 
}

This encourages lazy pipeline input: a positional list argument loads all data into memory at once, while implicit pipeline input processes elements one at a time.

CLI usage

For all available options and usage information, run:

nu-lint # Lint all Nu files in working directory
nu-lint --help

More than 100 rules are available on The CLI. Some of them need further testing and improvement. Please make an issue on the issue tracker to report any bugs. dead-code - Remove unused or redundant code

• avoid_self_import
• unnecessary_accumulate
• unnecessary_variable_before_return (auto-fix)
• redundant_ignore (auto-fix)
• unnecessary_mut (auto-fix)
• unused_helper_functions (auto-fix)

documentation - Improve relevance of actionability of user-facing messages.

• add_doc_comment_exported_fn
• descriptive_error_messages
• add_label_to_error
• add_help_to_error
• add_span_to_label
• add_url_to_error
• main_positional_args_docs
• main_named_args_docs
• max_positional_params

error-handling - Error handling best practices

• check_complete_exit_code
• descriptive_error_messages
• escape_string_interpolation_operators
• exit_only_in_main
• missing_stdin_in_shebang (auto-fix)
• non_final_failure_check
• use_error_make_for_catch (auto-fix)
• try_instead_of_do
• unsafe_dynamic_record_access (auto-fix)

external-tools - Replace common external CLI tools.

• use_builtin_curl (auto-fix)
• use_builtin_eza (auto-fix)
• use_builtin_fd (auto-fix)
• replace_jq_with_nu_get (auto-fix)
• use_builtin_rg (auto-fix)
• unnecessary_hat (auto-fix)
• use_builtin_wget (auto-fix)
• use_builtin_which (auto-fix)

formatting - Formatting according to Nushell guidelines.

• ansi_over_escape_codes (auto-fix)
• collapsible_if (auto-fix)
• forbid_excessive_nesting
• max_function_body_length
• replace_if_else_chain_with_match (auto-fix)
• brace_spacing (auto-fix)
• no_trailing_spaces (auto-fix)
• omit_list_commas (auto-fix)
• pipe_spacing (auto-fix)
• reflow_wide_pipelines (auto-fix)
• reflow_wide_lists (auto-fix)
• wrap_wide_records (auto-fix)

naming - Follow official naming conventions

• kebab_case_commands
• screaming_snake_constants
• snake_case_variables (auto-fix)
• add_label_to_error

performance - Rules with potential performance impact

• avoid_nu_subprocess
• dispatch_with_subcommands
• avoid_self_import
• turn_positional_into_stream_input (auto-fix)
• unnecessary_accumulate
• merge_multiline_print (auto-fix)

posix-tools - Replace common bash/POSIX commands.

• ignore_over_dev_null (auto-fix)
• use_builtin_awk (auto-fix)
• use_builtin_cat (auto-fix)
• use_builtin_cut (auto-fix)
• use_builtin_date (auto-fix)
• use_builtin_echo (auto-fix)
• use_builtin_find (auto-fix)
• use_builtin_grep (auto-fix)
• use_builtin_head (auto-fix)
• use_builtin_cd (auto-fix)
• use_builtin_ls (auto-fix)
• use_builtin_read (auto-fix)
• use_builtin_sed (auto-fix)
• use_builtin_sort (auto-fix)
• use_builtin_tail (auto-fix)
• use_builtin_uniq (auto-fix)
• use_builtin_wc (auto-fix)
• ansi_over_escape_codes (auto-fix)

side-effects - Handle risky and unpredictable commands.

• dangerous_file_operations
• errors_to_stderr
• avoid_mixed_io_types
• print_and_return_data
• silence_side_effect_only_each (auto-fix)

simplification - Simplify verbose patterns to idiomatic Nushell

• use_is_not_empty (auto-fix)
• dispatch_with_subcommands
• shorten_with_compound_assignment (auto-fix)
• lines_instead_of_split (auto-fix)
• lines_each_to_parse (auto-fix)
• simplify_regex_parse (auto-fix)
• split_row_first_last (auto-fix)
• split_row_get_to_parse (auto-fix)
• turn_positional_into_stream_input (auto-fix)
• replace_counter_while_with_each
• replace_loop_counter_with_range
• each_if_to_where (auto-fix)
• for_filter_to_where
• omit_it_in_row_condition (auto-fix)
• remove_redundant_in (auto-fix)
• where_or_filter_closure_to_it_row_condition (auto-fix)
• items_instead_of_transpose_each (auto-fix)
• merge_get_cell_path (auto-fix)
• merge_multiline_print (auto-fix)
• inline_single_use_function

type-safety - Encourage annotations with type hints.

• external_script_as_argument
• add_type_hints_arguments (auto-fix)
• prefer_path_type (auto-fix)
• typed_pipeline_io (auto-fix)

upstream - Forward warnings and errors of the upstream Nushell parser.

• nu_deprecated
• nu_parse_error

Installation

From crates.io:

cargo install nu-lint

Source

Build from source:

cargo install --path .

Nix

Run without installing (using flakes):

nix run git+https://codeberg.org/wvhulle/nu-lint

Editor extension

VS Code extension

Available at VS Code Marketplace.

Helix

Add to your ~/.config/helix/languages.toml:

[language-server.nu-lint]
command = "nu-lint"
args = ["--lsp"]

[[language]]
name = "nu"
language-servers = ["nu-lint"]

Neovim

Add to your Neovim configuration (Lua):

vim.lsp.config['nu-lint'] = {
  cmd = { 'nu-lint', '--lsp' },
  filetypes = { 'nu' },
  root_markers = { '.git' }
}
vim.lsp.enable('nu-lint')

Emacs

Add to your Emacs configuration (with Eglot, built-in since Emacs 29):

(with-eval-after-load 'eglot
  (add-to-list 'eglot-server-programs
               '(nushell-mode "nu-lint" "--lsp")))

Kate

Add to your ~/.config/kate/lspclient/settings.json:

{
  "servers": {
    "nushell": {
      "command": ["nu-lint", "--lsp"],
      "highlightingModeRegex": "^Nushell$"
    }
  }
}

Other

You can also implement your own editor extensions using the --lsp flag as in: nu-lint --lsp. This will spawn a language server compliant with the Language Server Protocol.

Configuration

Create .nu-lint.toml in your project root:

# This rule is ignored
ignored = ["snake_case_variables"]
max_pipeline_length = 80
pipeline_placement = "start"
# Set lint level of a set of rules at once.
[groups]
performance = "warning"
type-safety = "error"

# Override a single rule lievel
[rules]
dispatch_with_subcommands = "hint"