esm: end-of-life DEP0151 main index lookup

[anonrig]

Description

End-of-Life for DEP0151: main index lookup and extension searching for ES module import 'pkg' resolution.

All ES module main entry point resolutions now require an explicit "exports" or "main" entry with the exact file extension. The lookups that previously succeeded with a DEP0151 warning now throw ERR_INVALID_PACKAGE_CONFIG.

CommonJS packages are unchanged and can still use index lookup and extension searching.

Why

DEP0151 has been a runtime deprecation since v16.0.0 (documentation-only since v15.8.0 / v14.18.0). Resolving an ES module should always use an exact path, including file name and extension.

Behavior change (semver-major)

Before	After
import 'pkg' with { "type": "module" } and no main/exports — loads index.js with DEP0151	Throws ERR_INVALID_PACKAGE_CONFIG
import 'pkg' with { "type": "module", "main": "index" } — extension search + DEP0151	Throws ERR_INVALID_PACKAGE_CONFIG
import 'pkg' with { "type": "module", "main": "./index.js" }	Unchanged
import 'pkg' of a CommonJS package with no main	Unchanged

Changes

• lib/internal/modules/esm/resolve.js: replace emitLegacyIndexDeprecation() with throwIfLegacyIndexESM()
• doc/api/deprecations.md: mark DEP0151 as End-of-Life
• doc/api/packages.md / doc/api/esm.md: document the exact-extension requirement
• Tests: expect ERR_INVALID_PACKAGE_CONFIG instead of a DEP0151 warning

Test plan

• make lint-js — pass
• tools/lint-md/lint-md.mjs on changed docs — pass
• python3 tools/test.py targeted ESM tests — 6/6 pass
• python3 tools/test.py test/es-module — 243/243 pass

Refs: #37206
Refs: #36918

[nodejs-github-bot]

Review requested:

• @nodejs/loaders
• @nodejs/userland-migrations

[github-actions]

The notable-change PRs with changes that should be highlighted in changelogs. label has been added by @anonrig.

Please suggest a text for the release notes if you'd like to include a more detailed summary, then proceed to update the PR description with the text or a link to the notable change suggested text comment. Otherwise, the commit will be placed in the Other Notable Changes section.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (f83e7df) to head (343b8b2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65289      +/-   ##
==========================================
+ Coverage   90.31%   90.32%   +0.01%     
==========================================
  Files         751      751              
  Lines      249956   249953       -3     
  Branches    47204    47207       +3     
==========================================
+ Hits       225745   225770      +25     
+ Misses      15612    15563      -49     
- Partials     8599     8620      +21     

Files with missing lines	Coverage Δ
lib/internal/modules/esm/resolve.js	99.05% <100.00%> (-0.01%)	⬇️

... and 32 files with indirect coverage changes

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