Recognise boxed Error subclasses as Errors

[puskuruk]

instanceof Error, String(error) and the uncaught-exception describer did not recognise a boxed instance of a user class extending Error. Nest's exception filters depend on all three.

• a78565c Recognise a boxed instance of a class extending Error as an Error in instanceof, String() and the uncaught describer

A subclass that overrides toString() keeps its own text: String(error) and the uncaught describer take the dynamic conversion when the boxed instance's toString property is a function, and the base name: message formatter otherwise (CodeRabbit's review comment, which was right: the base method is not virtual).

Verification: npm run build passed, npm run gate -- --write exit 0 (0 drift rows on certified programs), node scripts/run-runtime-tests.mjs --only error-subclass 9 ok (including instanceof-error-over-boxed-error-subclass and string-of-boxed-error-subclass-overriding-tostring), prettier clean.

Related

Independent of the other three compiler fixes (#8, #9, #10); all four go into compiler release 1.0.38, which node-compat geastack/node-compat#8 (compile hello-nest ahead of time) needs.

Rebased onto main d281cde (1.0.41) on 2026-10-20; gate byte-identical and the runtime test green there.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of custom Error subclasses, including instanceof checks and exception reporting.
  • Preserved custom toString() behavior for errors and their subclasses.
  • Improved string conversion for boxed and non-error values.

• Tests

  • Added coverage for nested error subclasses, custom formatting, template interpolation, and caught-error behavior.

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📥 Commits

Reviewing files that changed from the base of the PR and between a78565c and 2dc9ee1.

📒 Files selected for processing: 5

• scripts/emitted-baseline-runtime.txt
• src/targets/cpp/runtime/gea_runtime.h
• test/runtime/instanceof-error-over-boxed-error-subclass.runtime.ts
• test/runtime/object-keys-over-recursive-dictionary-or-array-union.runtime.ts
• test/runtime/string-of-boxed-error-subclass-overriding-tostring.runtime.ts

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Reviewing files that changed from the base of the PR and between 098d356 and a78565c.

📒 Files selected for processing: 3

• scripts/emitted-baseline-runtime.txt
• src/targets/cpp/runtime/gea_runtime.h
• test/runtime/string-of-boxed-error-subclass-overriding-tostring.runtime.ts

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📝 Walkthrough

The C++ host runtime now recognizes direct Error values and custom Error subclasses. String conversion, instanceof checks, and exception reporting use this recognition. Runtime tests and emitted baselines cover subclass behavior and custom toString implementations.

Changes: Runtime Error Recognition

Layer / File(s)	Summary
Error reference retrieval src/targets/cpp/runtime/gea_runtime.h	The host runtime adds runtimeErrorOf and isErrorValue. Error extraction accepts direct Error payloads and class identities extending the runtime-error type.
Error formatting and runtime validation src/targets/cpp/runtime/gea_runtime.h, test/runtime/*, scripts/emitted-baseline-runtime.txt	String conversion honors custom toString functions and default Error formatting. instanceOfError and exception reporting recognize Error subclasses. Tests and emitted baselines cover inheritance, formatting, thrown values, and plain error-shaped objects.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: dashersw

Merge Risk: ⚪ Minimal · up to a7856

Boxed Error subclasses retain their custom string formatting, and no actionable merge-blocking risk remains after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 inconclusive

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (2 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: recognizing boxed subclasses of Error as errors.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (2 skipped: 1 unsupported, 1 too large.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

✨ Finishing Touches: 💡 1

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @src/targets/cpp/runtime/gea_runtime.h:
- Line 42997: Update the isErrorValue conversion branch and the
uncaught-exception formatter to use dynamic object-method conversion when an
Error subclass overrides toString(); retain runtimeErrorString for instances
selecting the base Error.toString method.

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ℹ️ Review info

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• Run ID: 208e3ba7-95da-4a48-9e3c-41c017699aa0

📥 Commits

Reviewing files that changed from the base of the PR and between f9154e8 and 098d356.

📒 Files selected for processing: 3

• scripts/emitted-baseline-runtime.txt
• src/targets/cpp/runtime/gea_runtime.h
• test/runtime/instanceof-error-over-boxed-error-subclass.runtime.ts

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