feat(validateSchema): support custom error generation

demo/src/index.js

@@ -81,6 +81,12 @@ const createFormContainer = compose(
     username: {
       required: true,
       maxLength: 8,
+      // note: you can optionally generate custom errors via `formatError`
+      // by providing a string or a function that receives context
+      formatError: (context) => {
+        // e.g. return a message id for use with `react-intl` or similar
+        return `errors.username.${context.condition}`;
+      }
     },
     password: {
       // note: my `test` implementation is super basic, `fail` can

src/validateSchema.js

@@ -8,20 +8,26 @@ const getValidationErrors = (schema, model) => Object.keys(schema).reduce((acc,
   const value = model[key]
   const rules = schema[key]
 
+  const renderError = (condition, fallback) => {
+    return typeof rules.formatError === 'function'
+      ? rules.formatError({ key, value, condition, rules, schema, model })
+      : fallback
+  }
+
   if (rules.required && !value) {
-    errors.push(`${key} is required`)
+    errors.push(renderError('required', `${key} is required`))
   }
   if (rules.type && typeof value !== rules.type) {
-    errors.push(`${key} must be of type ${rules.type}, but got ${typeof value}`)
+    errors.push(renderError('type', `${key} must be of type ${rules.type}, but got ${typeof value}`))
   }
   if (rules.minLength) {
     if (!value || value.length < rules.minLength) {
-      errors.push(`${key} must have at least ${rules.minLength} characters`)
+      errors.push(renderError('minLength', `${key} must have at least ${rules.minLength} characters`))
     }
   }
   if (rules.maxLength) {
     if (value && value.length > rules.maxLength) {
-      errors.push(`${key} must not have more than ${rules.maxLength} characters`)
+      errors.push(renderError('maxLength', `${key} must not have more than ${rules.maxLength} characters`))
     }
   }
   if (rules.test) {