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.

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.

Usage

(Editor integration is available, see below)

Lint all Nu files in working directory with:

nu-lint

To see all options and get help:

nu-lint --help

Rules

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

• The official Nu parser nu-check.
• The TreeSitter-based Nu formatter topiary-nushell.
• The official Nu style guide

Some of them need further testing and improvement. Please make an issue on the issue tracker to report any bugs. In early stages of development some rules may be replaced or renamed.

More than 100 rules are defined and most have automatic fixes available (list may be out-of-date):

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)
• no_export_main (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
• check_flag_before_use
• 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)

filtering - Better patterns for filtering and selecting data.

• each_if_to_where (auto-fix)
• for_filter_to_where
• omit_it_in_row_condition (auto-fix)
• where_or_filter_closure_to_it_row_condition (auto-fix)
• remove_redundant_in (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)

idiomatic - Use Nu-native idioms instead of verbose patterns.

• bare_string_okay (auto-fix)
• use_is_not_empty (auto-fix)
• dispatch_with_subcommands
• inline_single_use_function
• items_instead_of_transpose_each (auto-fix)
• merge_get_cell_path (auto-fix)
• merge_multiline_print (auto-fix)
• turn_positional_into_stream_input (auto-fix)
• shorten_with_compound_assignment (auto-fix)
• use_regex_operators (auto-fix)

iteration - Better patterns for loops and iteration.

• replace_loop_counter_with_range
• replace_counter_while_with_each

naming - Follow official naming conventions

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

parsing - Better ways to parse and transform text data.

• lines_instead_of_split (auto-fix)
• never_space_split (auto-fix)
• from_after_parsed_open (auto-fix)
• lines_each_to_parse (auto-fix)
• open_raw_from_to_open (auto-fix)
• simplify_regex_parse (auto-fix)
• split_row_first_last (auto-fix)
• split_row_get_to_parse (auto-fix)

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 patterns.

• ignore_over_dev_null (auto-fix)
• use_builtin_awk (auto-fix)
• use_builtin_bat (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)
• head_to_first (auto-fix)
• use_builtin_cd (auto-fix)
• use_builtin_ls (auto-fix)
• use_builtin_pager (auto-fix)
• use_builtin_read (auto-fix)
• use_builtin_sed (auto-fix)
• use_builtin_sort (auto-fix)
• use_builtin_tac (auto-fix)
• tail_to_last (auto-fix)
• use_builtin_uniq (auto-fix)
• use_builtin_wc (auto-fix)
• ansi_over_escape_codes (auto-fix)
• ansi_over_escape_codes (auto-fix)

side-effects - Handle risky and unpredictable commands.

• dangerous_file_operations
• errors_to_stderr
• dont_mix_different_effects
• print_and_return_data
• silence_side_effect_only_each (auto-fix)
• silence_stderr_data

type-safety - Annotate with type hints where possible.

• 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"]

# Some rules are configurable
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"