Extension host: use native source maps in development hosts

[Goga Koreli (gogakoreli)]

Summary

Related to #145473 and #238469. This is a local extension-development host first step, not a claim to resolve the broader request for source-mapped crash reports from shipped extensions.

A bundled extension can ship a valid source map and still produce generated-file locations in its error stacks. There are two independent pieces to address:

1. Enable Node's native source-map support before importing the extension host and its extensions.
2. Keep the host's extension-attribution walk, but use the previously installed Error.prepareStackTrace formatter when native source maps are enabled. Building the stack from CallSite.toString() bypasses Node's mapped formatting.

This PR uses module.setSourceMapsSupport(true) and adds no dependency, Module._load interception, or extension API. The flag is set by NativeLocalProcessExtensionHost only for development hosts. With source maps disabled, the existing formatter and its tab indentation remain unchanged. Existing handling of formatters installed by extensions remains in place.

The formatter composition follows Node's documented guidance and the pattern used by Babel. The captured hook is inferred, and the wrapper is contextually typed from typeof Error.prepareStackTrace, rather than asserting compatibility with a narrower call-site interface. Delegation preserves the Error receiver, and the native path skips unused fallback string rendering while retaining attribution.

Before / after

The new isolated-process regression fixture has a real CommonJS module with an external source map. Paths below are shortened; this is a test fixture, not a screenshot from a fully launched editor.

Before (existing host formatter, even with native maps enabled):

Error: source map probe
    at Object.createError (<fixture>/fixture.cjs:1:62)

After (native formatter preserved):

Error: source map probe
    at Object.createError (<fixture>/fixture.ts:1:1)

The fixture deliberately uses a single mapping segment to make the expected source location deterministic. The test also verifies that the same error reaches $onExtensionRuntimeError and extension telemetry with the correct extension identifier and stack. It does not just assert a fabricated formatter string.

Regression coverage

Nine new cases run in separate child processes because the host makes Error.prepareStackTrace non-configurable:

• Actual generated-to-source mapping using Node's formatter, with error and telemetry attribution preserved.
• Existing formatting and attribution with source maps disabled.
• Disabling source maps after handler installation.
• Custom formatters installed before and after the host handler, including their Error receiver.
• Zero fallback toString() calls when a formatter is selected, with attribution preserved.
• Bootstrap with the opt-in flag unset, false, and true.

I also ran the existing seven formatter-wrapping/re-wrapping tests for #184926.

To check the tests are sensitive to the change, I temporarily removed the proposed formatter delegation and bootstrap activation while retaining the original eight tests. Three cases failed: native mapping, the pre-installed formatter case, and bootstrap activation. Restoring the implementation made the suite pass.

For the review follow-up, I strengthened the custom-formatter cases to check the receiver and added an independently instrumented fallback-rendering case. Against the initial PR implementation, these exposed two failures: an incorrect receiver and one unnecessary fallback rendering call. Both pass after the revision.

Local validation

Public microsoft/vscode source based on 1f6488722c942d1d7528a7d949769a69e4a557c3, macOS arm64:

• npm run transpile-client — passed.
• npm run typecheck-client — passed.
• ESLint on all four changed files with --max-warnings 0 — passed.
• Node 24.18.0: nine new cases and seven existing cases passed (the Node runner additionally reports its own unexpected-error checks).
• VS Code's pinned Electron 43.7.3 / embedded Node 24.21.0: nine new cases and seven existing cases passed via scripts/test.sh.
• npm run valid-layers-check — passed.
• git-secrets with AWS patterns on all four contribution files — passed.
• git diff --check — passed.

Commands:

npm run test-node -- --run src/vs/workbench/api/test/node/extensionHostSourceMaps.test.ts
npm run test-node -- --run src/vs/workbench/api/test/common/extensionHostMain.test.ts
./scripts/test.sh --run src/vs/workbench/api/test/node/extensionHostSourceMaps.test.ts --grep 'Extension host native source maps'
./scripts/test.sh --run src/vs/workbench/api/test/common/extensionHostMain.test.ts --grep 'ExtensionHostMain#ErrorHandler'

The subprocess cases use Electron-as-Node when launched from the Electron test runner. A full UI/utility-process extension-host launch, Windows/Linux validation, and a representative startup/stack-formatting performance benchmark are not yet completed. Opening as a draft to make that validation scope explicit and discuss whether this is a useful first step.

Scope and prior work

• This is an alternative native-runtime approach to Add source-map-support for stack trace formatting in extensionHost debugging #238469, not a continuation of that PR or a claim to its authorship.
• No new opt-in policy for release, remote, or web extension hosts is introduced. The shared handler respects native source-map support when it is already enabled, but only local development hosts are newly enabled by this PR.
• ESM file: URL error-attribution behavior is a separate concern and is intentionally not included.
• No internal repository files or patch files are included; this branch was prepared against public VS Code source.

Would the maintainers be open to this dev-host-only first step? Happy to adjust the scope based on guidance.

Prepared with AI assistance. The local automated checks are listed above; maintainer review is still required.

[Copilot]

Copilot review overview

🟡 Changes recommended

Formatter receiver handling is incorrect, and native formatting currently duplicates avoidable stack-processing work.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Preserve Error receiver when invoking captured formatter · New
• Avoid redundant stack formatting with native source maps · New

What changed in this PR

Enables native source-map formatting for local extension-development hosts while retaining extension error attribution.

Changes:

• Activates Node source maps during extension-host bootstrap.
• Delegates stack formatting to Node when enabled.
• Adds subprocess regression coverage.

File	Description
src/​bootstrap-fork.ts	Enables native source maps before host loading.
src/​vs/​workbench/​api/​common/​extensionHostMain.ts	Preserves native formatting during attribution.
src/​vs/​workbench/​api/​test/​node/​extensionHostSourceMaps.test.ts	Tests mapping, attribution, formatters, and bootstrap flags.
src/​vs/​workbench/​services/​extensions/​electron-browser/​localProcessExtensionHost.ts	Enables source maps for development hosts.

---

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[Goga Koreli (gogakoreli)]

Fixed in e81fe03. The captured formatter is now called with Error as its receiver, and the before/after formatter tests use receiver-sensitive functions. I also removed the assertions by inferring the captured hook and contextually typing the wrapper from typeof Error.prepareStackTrace.

[Goga Koreli (gogakoreli)]

Fixed in e81fe03. Formatter selection now happens before the attribution walk, and fallback toString()/concatenation only runs when needed. Added a regression that checks zero fallback rendering calls while runtime-error and telemetry attribution still work; it fails against the previous implementation.

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