fix(core): preserve custom .stack getters in error/test formatter#35246
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Errors that provide a custom `.stack` (e.g. Effect or other fiber runtimes, or a manually assigned value) were rendered with an internal call-site frame instead of their custom stack. `console.error` already showed the rich stack because it formats via the `.stack` string, but letting the error bubble to the top-level handler or fail a test discarded it, since those paths render only the structured frames read from the private #callSiteEvals array. When accessing `.stack` does not populate #callSiteEvals, the stack was not produced by our prepareStackTrace, so the structured frames are not authoritative. Mark such errors with a new `stack_is_custom` flag on JsError and have the formatter emit the custom `.stack` string instead, matching Node.js. Closes #35243
The stack_is_custom heuristic flagged any frame-less error whose .stack spans more than one line. An error with a multi-line message (e.g. the "Unsupported scheme ... Supported schemes:" list) has no frames and a multi-line .stack that is just its "name: message" string, so it was wrongly classified as custom and the formatter re-emitted the message tail, duplicating it. Compare .stack against the default "name: message" representation and only treat it as custom when it carries content beyond that header, so a multi-line message is no longer mistaken for a stack.
bartlomieju
enabled auto-merge (squash)
June 17, 2026 08:39
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Errors that expose a custom `.stack` getter, such as those produced by
Effect and other fiber runtimes, or a manually assigned `.stack` string,
were rendered with a single internal call-site frame instead of the
custom stack. `console.error` already showed the rich stack because it
formats via the `.stack` string, but letting the same error bubble to
the top-level handler or fail a test discarded it: those paths render
only the structured frames read from the private `#callSiteEvals` array,
which a custom `.stack` never populates.
When accessing `.stack` does not populate `#callSiteEvals`, the stack was
not produced by our `prepareStackTrace`, so the structured frames are not
authoritative. This marks such errors with a new `stack_is_custom` flag
on `JsError` and has the formatter emit the custom `.stack` string in
that case, matching Node.js.
Closes #35243