spec-forms

A Clojure(Script) library for creating human-readable error messages from specs, with some helper functions for using those messages with Reforms.

The current version depends on spec-tools, but when spec-alpha2 is released, this dependency will be dropped and spec-forms will create Specs directly.

Install

Add to deps.edn:

code204/spec-forms {:mvn/version "0.1.0-alpha2"}
reforms {:mvn/version "0.4.3"}

Or add to project.clj:

[code204/spec-forms "0.1.0-alpha2"]
[reforms "0.4.3"]

Usage

Spec Creation

First, you need some specs. You can define error messages inline with the spec-forms.alpha/validator macro, or you can use normal specs in conjunction with the phrase library. We'll start with the validator macro. It takes two arguments: a predicate function to be called on the value, and an error message for when the predicate returns false, e.g.,

(require '[spec-forms.alpha :use validator])

(validator
  #(>= 16 (count %))
  "Must be 16 characters or less.")

The validator simply adds the message to the data returned by clojure.spec.alpha/explain-data, under the :reason key. If you happen to have existing code using spec-tools that returns a :reason, then you can use those specs with no changes.

An example .cljc file with a full spec definition:

(ns sf-test
  (:require [clojure.spec.alpha :as s]
            [clojure.string :as str]
            [spec-forms.alpha :as sf])
  #?(:cljs
     (:require-macros [clojure.spec.alpha])))

(defn max-length [n]
  (sf/validator
    #(>= n (count %))
    (str "Must be " n " characters or less.")))

(defn min-length [n]
  (sf/validator
    #(<= n (count %))
    (str "Must be at least " n " characters long.")))

(def non-blank
  (sf/validator
    #(and % (not (str/blank? %)))
    "Must not be blank"))
    
(s/def ::login (s/and (min-length 2) (max-length 4) non-blank))
(s/def ::password (s/and (min-length 2) (max-length 4) non-blank))

(s/def ::login-form (s/keys :req [::login ::password]))

Validation with clojure.spec

To validate on your own (rather than using reforms), just call spec.alpha/explain or spec.alpha/explain-data on any of the specs that you created earlier. explain prints the failure reason, while explain-data returns a vector of problems which each have a :reason key with the failure message.

(in-ns 'sf-test)

(s/explain ::login "")
;; "" - failed: Must be at least 2 characters long. spec: :sf-test/login
;= nil

(s/explain-data ::login "")
;=#:clojure.spec.alpha{:problems
                       ({:path [],
                         :pred
                         (clojure.core/fn
                          [%]
                          (clojure.core/<= n (clojure.core/count %))),
                         :val "",
                         :via [:sf-test/login],
                         :in [],
                         :reason
                         "Must be at least 2 characters long."}),
                       :spec :sf-test/login,
                       :value ""}

Form Validation

We use the Reforms validation helpers, but we use spec-forms.alpha.validate! instead of reforms.core/validate! The spec-forms validate! function takes four arguments: the data and ui-state atoms, the spec name, and an optional configuration map:

(spec-forms.alpha/validate! data ui-state :sf-test/login-form
   {:default-error-message "Oops!"})

The configuration map supports three options:

• :default-error-message A message to return if no other message is found. Default: "Failed validation"
• :message-fn A 2-argument function to be called with the problem as returned by clojure.spec.alpha/explain-data and the configuration map. It should return a String. It's this function's responsibility to parse the :reason of the problem and return the :default-error-messsage.
• :required-key-message This is used when a key is not present in the form but is required, as when clojure.spec.alpha/keys is used. The validator for the key will not be called due to the design of Clojure Spec. It can be a function that will receive the missing key (if you'd like different messages for different keys), or a String used for all keys. Default: "Required".

Reforms implements form data as a map, so we will need a map definition in our spec, such as (s/def ::login-form (s/keys :req [::login ::password])) in the Usage example earlier. ::login-form is the spec name which we give as the third argument of validate!. data is an atom containing the form data map. ui-state is an atom (initially nil) that Reforms uses to keep track of validation errors. See the Reforms docs for more information.

An example implementation using Rum (you'll need to add rum-reforms as a dependency to run this):

(ns sf-test.client
  (:require [clojure.spec.alpha :as s]
            [reforms.rum :include-macros true :as f]
            [reforms.validation :include-macros true :as v]
            [rum.core :as rum :refer (defcs)]
            [spec-forms.alpha :as sf]
            [sf-test]))

(defn login!
  [data ui-state]
  (when (sf/validate! data ui-state :sf-test/login-form)
    (js/alert "Logged in!")))

(defcs login-form
  < (rum/local nil ::ui-state)
  [state data]
  (let [comp (:rum/react-component state)
        ui-state (::ui-state state)]
    (v/form
      ui-state
      (v/text "Login" data [:sf-test/login])
      (v/password "Password" data [:sf-test/password])
      (f/form-buttons
        (f/button-primary "Log In"
          #(do (login! data ui-state)
               (rum/request-render comp)))))))

(defn mount-form []
  (rum/mount
   (login-form (atom nil))
   (js/document.getElementById "app")))

(defn init []
  (js/console.log "init")
  (mount-form))

Using with phrase

It's very simple to use phrase with spec-forms. We just need to create a custom message-fn and pass it as an option to validate!:

(require 'phrase.alpha 'spec-forms.alpha)

(defn spec-problem->message [{:keys [reason val via]} opts]
  (or reason
    (phrase.alpha/phrase-first {} (last via) val)
    (:default-failure-message opts "Failed validation")))

Wherever you call validate!:

(spec-forms.alpha/validate! data ui-state :your-spec-ns/your-spec
  {:message-fn spec-problem->message})