feat(typescript): add isolatedModules option for export type / import type support

[chengyixu]

Description

Adds a new isolatedModules option to TypeScriptOptions (default: false, opt-in). When set to true with ESM named exports, the generator emits export type { } for type-only models (interfaces, type aliases) and import type { } for cross-model dependencies.

This fixes TS1205: Re-exporting a type when 'isolatedModules' is enabled requires using 'export type'. errors that occur in Next.js, SWC, and esbuild projects.

Before (broken with isolatedModules: true):

interface ErrorPayload {
  type: 'error';
  message: string;
}
export { ErrorPayload }; // TS1205 error

After (with isolatedModules: true):

interface ErrorPayload {
  type: 'error';
  message: string;
}
export type { ErrorPayload }; // isolatedModules compatible

Key design decisions:

• Enums are always exported as export { } (never export type) because they compile to runtime JavaScript values.
• The option is opt-in (isolatedModules: false by default) so existing users are unaffected.
• Cross-model dependencies also use import type { } when the flag is enabled and the imported model is type-only.

Usage:

const generator = new TypeScriptGenerator({
  modelType: 'interface',
  moduleSystem: 'ESM',
  isolatedModules: true, // new option
});
const models = await generator.generateCompleteModels(doc, { exportType: 'named' });

Related Issue

Closes #2429

Checklist

• The code follows the project's coding standards and is properly linted (npm run lint).
• Tests have been added or updated to cover the changes.
• Documentation has been updated to reflect the changes.
• All tests pass successfully locally.(npm run test).

Additional Notes

• 9 new unit tests in TypeScriptDependencyManager.spec.ts covering all export/import type combinations.
• 2 new integration tests + snapshots in TypeScriptGenerator.spec.ts validating end-to-end output.
• All 110 existing TypeScript generator tests continue to pass.

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[chengyixu]

Hi @Samridhi-98 — just created this PR adding isolatedModules support for TypeScript ESM exports. This fixes TS1205 errors in Next.js/SWC/esbuild projects. All CI checks are passing (SonarCloud). Would love a review when you have a chance. Happy to adjust anything!

[chengyixu]

Hi @Samridhi-98 — you've been requested to review this PR. It adds an isolatedModules TypeScript option that emits export type { } for type-only models, fixing TS1205 errors in Next.js/SWC/esbuild projects. All CI checks are passing (SonarCloud, lint). Would appreciate your review when you get a chance! Happy to make any adjustments needed.

[chengyixu]

Hi @jonaslagoni @magicmatatjahu — this PR adds an isolatedModules option to the TypeScript generator, emitting export type { } for type-only models to fix TS1205 errors in Next.js/SWC/esbuild projects. SonarCloud and Netlify checks are passing. The fork workflow CI (Lint PR title, PR testing) needs maintainer approval to run. Would appreciate a review or CI approval when you get a chance. Happy to adjust anything!

[chengyixu]

Hi! This PR is CI green and ready for merge when you have a moment. Thanks!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud