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Configuration

For an overview of all available linters, go here.

Table of contents:

Introduction

Clj-kondo can be configured in five ways, by providing:

  • home dir config in ~/.config/clj-kondo/config.edn (respects XDG_CONFIG_HOME)
  • project config: a config.edn file in the .clj-kondo directory (see project setup)
  • :config-paths in project config.edn: a list of directories that provide additional config
  • command line --config file or EDN arguments
  • namespace local config using :clj-kondo/config metadata in the namespace form

The configurations are merged in the following order, where a later config overrides an earlier config:

  • home dir config
  • :config-paths in project config
  • project config
  • command line config
  • namespace local config

The ^:replace metadata hint can be used to replace parts or all of the configuration instead of merging with previous ones. The home dir config is implicitly part of :config-paths. To opt out of merging with home dir config use :config-paths ^:replace [] in your project config.

Note that namespace local config must always be quoted: {:clj-kondo/config '{:linters ...}} and quotes should not appear inside the config.

Look at the default configuration for all available options.

Examples

See the config project for library-specific configurations.

Unrecognized macros

Clj-kondo only expands a selected set of macros from clojure.core and some popular community libraries. For unrecognized macros you can use these configurations:

Linters

Each linter is identified by a keyword in the :linters config. We will start with general linter configutation and will then enumerate all available linters and corresponding config options.

Enabling and disabling

Disable a linter

$ echo '(select-keys [:a])' | clj-kondo --lint -
<stdin>:1:1: error: wrong number of args (1) passed to clojure.core/select-keys
linting took 10ms, errors: 1, warnings: 0

$ echo '(select-keys [:a])' | clj-kondo --lint - --config '{:linters {:invalid-arity {:level :off}}}'
linting took 10ms, errors: 0, warnings: 0

Enable optional linters

Some linters are not enabled by default. Right now these linters are:

  • :missing-docstring: warn when public var doesn't have a docstring.
  • :unsorted-required-namespaces: warn when namespaces in :require are not sorted.
  • :refer: warn when there is any usage of :refer in your namespace requires.
  • :single-key-in: warn when using assoc-in, update-in or get-in with single key.
  • :shadowed-var: warn when a binding shadows a var.

You can enable these linters by setting the :level:

{:linters {:missing-docstring {:level :warning}}}

Disable all linters but one

You can accomplish this by using ^:replace metadata, which will override instead of merge with other configurations:

$ clj-kondo --lint corpus --config '^:replace {:linters {:redundant-let {:level :info}}}'
corpus/redundant_let.clj:4:3: info: redundant let
corpus/redundant_let.clj:8:3: info: redundant let
corpus/redundant_let.clj:12:3: info: redundant let

Ignore warnings in an expression

To ignore all warnings in an expression, place a hint before it. It uses reader comments, so they won't end up in your runtime.

#_:clj-kondo/ignore
(inc 1 2 3)

To ignore warnings from just one or a few linters:

#_{:clj-kondo/ignore [:invalid-arity]}
(inc 1 2 3)

To ignore warnings for only one language in a reader conditional:

#_{:clj-kondo/ignore #?(:clj [:unused-binding] :cljs [])}
(defn foo [x]
  #?(:cljs x)) ;; x is only used in cljs, but unused is ignored for clj, so no warning

Lint a custom macro like a built-in macro

In the following code the my-defn macro is defined, but clj-kondo doesn't know how to interpret it:

(ns foo)

(defmacro my-defn [name args & body]
  `(defn ~name ~args
     (do (println "hello!")
       ~@body)))

(my-defn foo [x])

Hence (foo 1 2 3) will not lead to an invalid arity error. However, the syntax of my-defn is a subset of clojure.core/defn, so for detecting arity errors we might have just linted it like that. That is what the following configuration accomplishes:

{:lint-as {foo/my-defn clojure.core/defn}}

When you have custom def or defn-like macros and you can't find a supported macro that is like it, you can use:

{:lint-as {foo/my-defn clj-kondo.lint-as/def-catch-all}}

Ignore the contents of comment forms

If you prefer not to lint the contents of (comment ...) forms, use this configuration:

{:skip-comments true}

Available linters

See linters.md.

Hooks

See hooks.md.

Output

Print results in JSON format

$ clj-kondo --lint corpus --config '{:output {:format :json}}' | jq '.findings[0]'
{
  "type": "invalid-arity",
  "filename": "corpus/nested_namespaced_maps.clj",
  "row": 9,
  "col": 1,
  "level": "error",
  "message": "wrong number of args (2) passed to nested-namespaced-maps/test-fn"
}

Printing in EDN format is also supported.

Print results with a custom format

$ clj-kondo --lint corpus --config '{:output {:pattern "::{{level}} file={{filename}},line={{row}},col={{col}}::{{message}}"}}'
::warning file=corpus/compojure/core.clj,line=2,col=19::Unsorted namespace: foo

The custom pattern supports these template values:

Template Variable Notes
{{filename}} File name
{{row}} Row where linter violation starts
{{col}} Column where linter violation starts
{{level}} Lowercase level of linter warning, one of info,warn,error
{{LEVEL}} Uppercase variant of {{level}}
{{message}} Linter message

Include and exclude files from the output

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:include-files ["^clojure/test"]}}'
clojure/test.clj:496:6: warning: redundant let
clojure/test/tap.clj:86:5: warning: redundant do
linting took 3289ms, errors: 0, warnings: 2

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:include-files ["^clojure/test"] :exclude-files ["tap"]}}'
clojure/test.clj:496:6: warning: redundant let
linting took 3226ms, errors: 0, warnings: 1

Show progress bar while linting

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:progress true}}'
.................................................................................................................
cljs/tools/reader.cljs:527:9: warning: redundant do
(rest of the output omitted)

Output canonical file paths

The config '{:output {:canonical-paths true}}' will output canonical file paths (absolute file paths without ..). This also shows the full path of a jar file when you lint a classpath.

$ clj-kondo --lint corpus --config '{:output {:canonical-paths true}}'
/Users/borkdude/dev/clj-kondo/corpus/cljc/datascript.cljc:8:1: error: datascript.db/seqable? is called with 2 args but expects 1
(rest of the output omitted)

Example configurations

These are some example configurations used in real projects. Feel free to create a PR with yours too.

Also see the config project.

Exporting and importing configuration

Libraries can export configuration on the classpath. When a users lints using a project classpath, these configurations are automatically detected and imported into the .clj-kondo directory. To export config, make sure there is a directory in your library with the following structure:

clj-kondo.exports/<your-org>/<your-libname>

The clj-kondo/config repo has configurations and hook code for several libraries:

$ tree -d -L 3 resources
resources
└── clj-kondo.exports
    └── clj_kondo
        ├── claypoole
        ├── fulcro
        ├── mockery
        ├── rum
        └── slingshot

Note that this library uses the org clj-kondo to not conflict with configurations that the orgs of the libraries themselves might use for exporting configuration. If the claypoole library itself wanted to export config, the structure might look like:

resources
└── clj-kondo.exports
    └── com.climate
        └── claypoole

Suppose you would have clj-kondo/config on your classpath and linted like this:

$ clj-kondo --no-warnings --lint "$(clojure -Spath -Sdeps '{:deps {clj-kondo/config {:git/url "https://github.com/clj-kondo/config" :sha "e2e156c53c6c228fee7242629b41013f3e55051d"}}}')"
Copied config to .clj-kondo/clj-kondo/claypoole. Consider adding clj-kondo/claypoole to :config-paths in .clj-kondo/config.edn.
...

When configurations are found, instructions are printed how to opt in to those, namely by adding the imported configs to :config-paths in .clj-kondo/config.edn, like so:

{:config-paths ["clj-kondo/claypoole"]}

Imported configurations can be checked into source control, at your convenience.

Note: configuration is only copied when all of these requirements are met:

  • There is a .clj-kondo directory that can be used as a target.
  • The --no-warnings flag is used to indicate that clj-kondo is used to populate the cache.

Deprecations

Some configuration keys have been renamed over time. The default configuration is always up-to-date and we strive to mantain backwards compatibility. However, for completeness, you can find a list of the renamed keys here.

  • :if -> :missing-else-branch

Can you improve this documentation? These fine people already did:
Michiel Borkent, Davide Taviani, sogaiu, D. Ben Knoble, Khalid Jebbari, Jakob Durstberger, Robert Stuttaford, Lee Read, Raymond Huang, Andrey Orst & Erik Assum
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