Bug: IconPrefix should be typed to the specific icon group per package

[jernaumorat]

Bug description

Hi all, I'm using @fortawesome/pro-duotone-svg-icons and @fortawesome/pro-duotone-svg-icons, which type exported icons as: type IconDefinition = { IconPrefix: 'far' | 'fad' | 'all-other-prefixes', ... }.
The "bug" is that each package should type the IconPrefix of its exports to only the prefix(es) supported by that package.
For example: @fortawesome/pro-duotone-svg-icons would export icons as type IconDefinition = { IconPrefix: 'fad', ... } explicitly, allowing compile-time checking of the icon class used.

I've tried using type declarations to override this typing, but it seems .d.ts files can only extend, not override types; so the only workaround would be to patch the package or perform a runtime check.

I would be happy to submit a PR for this myself but I'm unsure how as this affects Pro packs.

Font Awesome version

v6.6.0

Application and Operating System

• TypeScript 5.4.5

Web bug report checklist

• I have included a test case because my odds go way up that the team can fix this when I do
• I have searched for existing issues and to the best of my knowledge this is not a duplicate

[jernaumorat]

Looking at the free-regular-svg-icons typing, it seems this could be tricky/hacky without converting some of the fontawesome-common-types types to generics, as all icons across all packs are typed as the same IconDefinition. IconDefinition could be updated to type IconDefinition<T extends IconPrefix> = { prefix: T, ... }, but this would be a breaking change for consumers of @fort-awesome/fontawesome-common-types/IconDefinition

This could be done per package (without breaking common-types) by modifying IconDefinition:

import { IconDefinition as IconDefinitionBase } from 'fontawesome-common-types';
type IconDefinition = Omit<IconDefinitionBase, 'prefix'> & { prefix: 'far' };