fix(types): preserve macro resolve unions

[lxy2500798479]

Summary

• preserve union object values from macro resolve instead of intersecting them into never
• keep existing intersection behavior for schema/response macro context merging
• add a regression test for a macro whose resolve returns different object shapes

Fixes #1891

Reproduction

A macro resolve returning { user: { id } } | { user: { id }, admin: true } previously inferred user as never inside the route handler. The new type test verifies user remains { id: string } and admin remains boolean | undefined.

Boundary report

• scoped to type-level macro context merging only
• runtime macro behavior unchanged
• multiple macro resolve fields still merge into one route context
• schema and response macro merging still use the existing intersection path

Tests

• bun run test:types
• bun test test/macro/macro.test.ts
• bun test
• bun run test:imports
• bun run build
• bun run test:node

Note: bun run test executes test:node without building dist first in this checkout, so test:node fails from missing dist/index.js unless bun run build runs first. After building, bun run test:node passes.

Summary by CodeRabbit

• Bug Fixes
  • Improved type inference for macros that resolve to unions of different object shapes. Conditional properties are now correctly inferred as optional or required based on whether they appear across all resolved shapes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: d5d92ff0-82ad-4f2e-a4a9-5fd82e3adcae

📥 Commits

Reviewing files that changed from the base of the PR and between 56310be and 98ba2ce.

📒 Files selected for processing (2)

• src/types.ts
• test/types/macro.ts

---

Walkthrough

This PR fixes a type-level regression where macro resolves returning unions of different object shapes were incorrectly inferred as never. The fix introduces type utilities to properly merge object unions and updates macro context inference to preserve union structure for the resolve field.

Changes

Union object merge for macro resolve typing

Layer / File(s)	Summary
Union merge type utilities src/types.ts	Adds UnionKeys, UnionValue, and MergeObjectUnion type utilities to extract union structure and merge object unions into a single object where each property represents the union of values across the input union objects.
Macro context mapping for resolve field src/types.ts	Modifies InnerMacroToContext to apply MergeObjectUnion to resolve field mapping, replacing the UnionToIntersect behavior that was collapsing union-of-objects to never.
Regression test for resolve union shapes test/types/macro.ts	Verifies macro with resolve returning { user: { id: 'a' } } | { user: { id: 'b' }, admin: true } correctly types user as { id: string } and admin as boolean | undefined in handler context.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• elysiajs/elysia#1691: Changes to InnerMacroToContext resolve field mapping could impact function-syntax macro overloads that depend on previous macro resolve type inference.

Poem

✧ a union in distress ✧

Union shapes collapsed, you dumb dumb～ ( ´థ౪థ)

Now merged and blessed, perfectly confused♡

Elysia's types are served, arrogantly used ᐡ・ﻌ・ᐡ

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main fix: preserving union types in macro resolve instead of collapsing them to never.
Linked Issues check	✅ Passed	The PR fully addresses #1891 by fixing union collapse regression, adding type-level test case, and preserving union-per-property behavior while maintaining intersection semantics for schema/response.
Out of Scope Changes check	✅ Passed	All changes are scoped to type-level macro context merging and regression testing; no unrelated runtime modifications or side changes present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

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🔧 ESLint

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src/types.ts

Oops! Something went wrong! :(

ESLint: 9.39.4

Error: ESLint configuration in --config » plugin:sonarjs/recommended is invalid:

• Unexpected top-level property "name".

Referenced from: /.eslintrc.json
at ConfigValidator.validateConfigSchema (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:2277:19)
at ConfigArrayFactory._normalizeConfigData (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3123:19)
at ConfigArrayFactory._loadExtendedPluginConfig (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3346:25)
at ConfigArrayFactory._loadExtends (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3259:29)
at ConfigArrayFactory._normalizeObjectConfigDataBody (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3199:25)
at _normalizeObjectConfigDataBody.next (<anonym

... [truncated 291 characters] ...

/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:2952:16)
at createCLIConfigArray (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3768:35)
(node:2) ESLintRCWarning: You are using an eslintrc configuration file, which is deprecated and support will be removed in v10.0.0. Please migrate to an eslint.config.js file. See https://eslint.org/docs/latest/use/configure/migration-guide for details. An eslintrc configuration file is used because you have the ESLINT_USE_FLAT_CONFIG environment variable set to false. If you want to use an eslint.config.js file, remove the environment variable. If you want to find the location of the eslintrc configuration file, use the --debug flag.
(Use node --trace-warnings ... to show where the warning was created)

test/types/macro.ts

Oops! Something went wrong! :(

ESLint: 9.39.4

Error: ESLint configuration in --config » plugin:sonarjs/recommended is invalid:

• Unexpected top-level property "name".

Referenced from: /.eslintrc.json
at ConfigValidator.validateConfigSchema (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:2277:19)
at ConfigArrayFactory._normalizeConfigData (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3123:19)
at ConfigArrayFactory._loadExtendedPluginConfig (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3346:25)
at ConfigArrayFactory._loadExtends (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3259:29)
at ConfigArrayFactory._normalizeObjectConfigDataBody (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3199:25)
at _normalizeObjectConfigDataBody.next (<anonym

... [truncated 291 characters] ...

/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:2952:16)
at createCLIConfigArray (/node_modules/.pnpm/@eslint+eslintrc@3.3.5/node_modules/@eslint/eslintrc/dist/eslintrc.cjs:3768:35)
(node:2) ESLintRCWarning: You are using an eslintrc configuration file, which is deprecated and support will be removed in v10.0.0. Please migrate to an eslint.config.js file. See https://eslint.org/docs/latest/use/configure/migration-guide for details. An eslintrc configuration file is used because you have the ESLINT_USE_FLAT_CONFIG environment variable set to false. If you want to use an eslint.config.js file, remove the environment variable. If you want to find the location of the eslintrc configuration file, use the --debug flag.
(Use node --trace-warnings ... to show where the warning was created)

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