Resolver: Fall through unmatched nested conditions

[maximilliangrand]

Summary

Metro stops resolving conditions after entering a matching parent, even when none of that parent's nested conditions match. For example, with react-native asserted and a CommonJS import, this export fails instead of selecting ./fallback.js:

{
  "exports": {
    "./feature": {
      "react-native": {"import": "./feature.mjs"},
      "default": "./fallback.js"
    }
  }
}

Resolve nested conditions recursively and continue to the next parent condition only when the nested object has no matching target. This follows Node's nested-condition semantics and applies to both exports and imports. Explicit null exclusions and invalid targets stop resolution; unmatched exact subpaths retain precedence over wildcard patterns. Numeric and boolean targets report invalid package configuration, and unsupported nested arrays retain their blocked behavior.

Changelog: [Fix] Resolve parent fallback conditions when a nested package exports or imports condition has no matching target

AI-assisted implementation and testing.

Test plan

On macOS with Node.js 26.7.0 and the frozen Yarn lockfile:

• Before the fix, the six new parent-fallback regressions failed against upstream; the existing tests and null/invalid-string controls passed.
• node node_modules/jest/bin/jest.js packages/metro-resolver/src/__tests__/package-exports-test.js packages/metro-resolver/src/__tests__/package-imports-test.js --runInBand — all 77 tests passed. Cases cover unmatched, empty, and deeper nested objects; later named/default conditions; null exclusions; invalid strings/numbers/booleans; and unsupported nested arrays.
• node node_modules/jest/bin/jest.js packages/metro-resolver --runInBand — 145 tests and 14 snapshots passed.
• node node_modules/jest/bin/jest.js --ci --maxWorkers 4 — 158 suites, 2,956 tests, and 487 snapshots passed; 14 tests skipped.
• node node_modules/flow-bin/cli.js check --timeout 90 — no errors.
• node node_modules/eslint/bin/eslint.js . --cache and node node_modules/prettier/bin/prettier.cjs --check . — passed.
• yarn run build, yarn run typecheck-ts, and yarn run test-smoke — passed.

The fallback, null, and invalid-target expectations were also checked against Node.js resolution using temporary packages. Node supports additional array shapes that Metro already treats as unsupported; this change preserves Metro's existing array behavior. Windows/Linux and other Node versions were not run locally.

[robhogan]

Looks good, thanks @maximilliangrand !

I've pushed a couple of small changes:

• Metro's convention doesn't distinguish null and undefined so I've swapped undefined for a NO_MATCH local symbol.
• preferred test.each so it's clearer which cases fail if there's ever a regression.

A possible follow-up is the still-incorrect handling of arrays - if we support them at all we should align with Node.

Thanks again