Use type predicates for isLocale and isNamespace functions

[mateuszaliyev]

I think recently added isLocale and isNamespace functions would be perfect use cases for type predicates. Thanks to this feature TypeScript would be able to narrow down the type of passed locale/namespace parameters.

Current implementation:

With type predicates:

Adding locale is Locales and namespace is Namespaces as a return type of isLocale and isNamespace functions is all that's needed. Note that it should also work with JSDoc @returns annotation (@returns {locale is Locale}).

I tried implementing this feature myself by following the CONTRIBUTING.md file but I couldn't figure out the testing part of generator files (regardless of multiple pnpm test and pnpm test:update-generated-files calls, it would not generate any files) so I'm creating a discussion instead. Just in case it happens to be useful, those are the changes I made:

packages/generator/src/files/generate-util.mts

`
${jsDocFunction('locale is Locales', {
  type: 'string',
  name: 'locale',
})}
export const isLocale = (locale${type('string')})${typePredicate('locale', 'Locales')} => locales.includes(${jsDocType(
  'Locales',
  `locale${typeCast('Locales')}`,
)})
${usesNamespaces ? `
${jsDocFunction('namespace is Namespaces', {
 type: 'string',
 name: 'namespace',
})}
export const isNamespace = (namespace${type('string')})${typePredicate('namespace', 'Namespaces')} => namespaces.includes(${jsDocType(
  'Namespaces',
  `namespace${typeCast('Namespaces')}`,
)})` : ''}
`

packages/generator/src/output-handler.mts

export const configureOutputHandler = (config: GeneratorConfigWithDefaultValues, version: TypescriptVersion): void => {

  /* ... */
  
  typePredicate = (param, type) => (shouldGenerateJsDoc ? '' : ` ${param} is ${type}`)
  
  /* ... */
  
}

/* ... */

export let typePredicate: (param: string, type: string) => string

[ivanhofer]

Thanks @mateuszaliyev! Indeed this would be a great feature, I didn't think of when I have implemented the function.

Can you please share what didn't work for you?

And thanks for your detailed examples!

[mateuszaliyev]

Glad I could help!

I tried to follow instructions inside of CONTRIBUTING.md file. I forked the repo, cloned it, ran pnpm test and pnpm test:update-generated-files. I'm probably understanding it wrong though, but I expected some files like packages\generator\test\generated\adapter-react\util.expected.ts to reflect my changes, just like here. Nothing was generated, so I've decided to create a discussion instead.

[ivanhofer]

What operating system are you using? Which node version?

[mateuszaliyev]

Windows 11 Home 21H2
Node v16.15.1

[ivanhofer]

Ok, I'll try to take a look this week and see if I can reproduce the issue

[ivanhofer]

I have made the changes and released version 5.15.0 right now