feat(validation-messages): displayName function

doc/article/en-US/validation-basics.md

@@ -66,7 +66,7 @@ To begin defining a ruleset, use the `ValidationRules` class. Start by targeting
 
 ### displayName
 
-Once you've targetted a property using `ensure` you can define the property's display name using `.displayName(name: string)`. Display names are used in validation messages. Specifying a display name is optional. If you do not explicitly set the display name the validation engine will attempt to compute the display name for you by splitting the property name on upper-case letters. A `firstName` property's display name would be `First Name`.
+Once you've targetted a property using `ensure` you can define the property's display name using `.displayName(name: string|ValidationDisplayNameAccessor)`. Display names are used in validation messages. Specifying a display name is optional. If you do not explicitly set the display name the validation engine will attempt to compute the display name for you by splitting the property name on upper-case letters. A `firstName` property's display name would be `First Name`.
 
 <code-listing heading="displayName">
   <source-code lang="ES 2015">
@@ -98,6 +98,7 @@ All rules have a standard message that can be overriden on a case-by-case basis
 * `$value`: the property value (at the moment the validation rule was executed).
 * `$object`: the object that owns the property.
 * `$config`: an object containing the rule's configuration. For example, the config for a `minLength` rule will have a `length` property.
+* `$getDisplayName`:  returns a displayable name of a property given the property name (irrespective of the property's displayName), split on capital letters, first letter ensured to be capitalized.
 
 Here's an example:
 

src/implementation/rule.ts

@@ -1,5 +1,7 @@
 import { Expression } from 'aurelia-binding';
 
+export type ValidationDisplayNameAccessor = () => string;
+
 /**
  * Information related to a property that is the subject of validation.
  */
@@ -12,7 +14,7 @@ export interface RuleProperty {
   /**
    * The displayName of the property (or object).
    */
-  displayName: string | null;
+  displayName: string | ValidationDisplayNameAccessor | null;
 }
 
 /**

src/implementation/standard-validator.ts

@@ -73,6 +73,8 @@ export class StandardValidator extends Validator {
       $value: value,
       $object: object,
       $config: rule.config,
+      // returns the name of a given property, given just the property name (irrespective of the property's displayName)
+      // split on capital letters, first letter ensured to be capitalized
       $getDisplayName: this.getDisplayName
     };
     return expression.evaluate(

src/implementation/validation-messages.ts

@@ -51,9 +51,9 @@ export class ValidationMessageProvider {
    * Override this with your own custom logic.
    * @param propertyName The property name.
    */
-  public getDisplayName(propertyName: string, displayName: string|null|undefined): string {
+  public getDisplayName(propertyName: string, displayName?: string|null|Function): string {
     if (displayName !== null && displayName !== undefined) {
-      return displayName;
+      return (displayName instanceof Function) ? displayName() : displayName as string;
     }
 
     // split on upper-case letters.

src/implementation/validation-rules.ts

@@ -3,6 +3,7 @@ import { ValidationParser, PropertyAccessor } from './validation-parser';
 import { isString } from './util';
 import { Rules } from './rules';
 import { validationMessages } from './validation-messages';
+import { ValidationDisplayNameAccessor } from './rule';
 
 /**
  * Part of the fluent rule API. Enables customizing property rules.
@@ -223,7 +224,7 @@ export class FluentRules<TObject, TValue> {
   /**
    * Sets the display name of the ensured property.
    */
-  public displayName(name: string) {
+  public displayName(name: string | ValidationDisplayNameAccessor | null) {
     this.property.displayName = name;
     return this;
   }

test/validation-messages.ts

@@ -20,5 +20,6 @@ describe('ValidationMessageProvider', () => {
     expect(messageProvider.getDisplayName('fooBar', undefined)).toBe('Foo Bar');
     expect(messageProvider.getDisplayName('foo bar', undefined)).toBe('Foo bar');
     expect(messageProvider.getDisplayName('foo', 'hello')).toBe('hello');
+    expect(messageProvider.getDisplayName('foo', () => 'hello')).toBe('hello');
   });
 });