error: don't double source-map rethrown frames after reading .stack

[robobun]

Fixes #15859.

Repro

import * as i1 from "util";
import * as i2 from "util";
import * as i3 from "util";
function err() {
    throw new Error()
};
function f1(){
    err()
}
function f2(){

}
try {
    f1();
} catch (error: any) {
    let x = error.stack
    throw error
}

Before:

Error:
      at err (test.ts:5:15)
      at f1 (test.ts:13:5)

After (matches error.stack):

Error:
      at err (test.ts:5:15)
      at f1 (test.ts:8:5)
      at test.ts:14:5

Cause

Reading error.stack causes JSC to clear m_stackTrace after materializing the string. On the rethrow, fromErrorInstance has no live StackFrame vector and falls back to parsing the .stack string with V8StackTraceIterator, which sets remapped = true on every parsed frame (the positions are already source-mapped).

remap_zig_exception checked that flag for the top frame but not in the loop over the remaining frames, so each non-top frame was fed back through resolve_source_mapping and remapped a second time. With three unused imports stripped by the transpiler, source line 8 is generated line 5; remapping source 8 as if it were generated yields source 13.

Separately, V8StackTraceIterator treated a line of the form at /path:line:col (no function name, no parentheses) as end-of-stack, dropping the anonymous top-level frame.

Fix

• remap_zig_exception: skip frames with remapped == true in the non-top loop (matching the top-frame check and remap_stack_frame_positions).
• V8StackTraceIterator::parseFrame: when no parentheses are present, parse the whole line as sourceURL:line:col with an empty function name (handles at <url>:<l>:<c> and at async <url>:<l>:<c>).

Verification

test/regression/issue/15859.test.ts has three cases (wrong-line, dropped frame, printed-frames-match-error.stack). All three fail on 1.4.0-canary.1+1498d7b77 and pass with this change.

[robobun]

Duplicate of #36602, which already includes both changes needed for #15859 (the frames[i].remapped skip in remap_zig_exception and the V8StackTraceIterator no-paren frame handling). Closing this in favor of that PR. The regression test here (test/regression/issue/15859.test.ts) is available on this branch if wanted.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between f91d5c9 and 79d52a2.

📒 Files selected for processing (3)

• src/jsc/VirtualMachine.rs
• src/jsc/bindings/ZigException.cpp
• test/regression/issue/15859.test.ts

---

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[robobun]

^{Updated 4:13 AM PT - Aug 1st, 2026}

@robobun, your commit 79d52a2 is building: #87194

[github-actions]

If you need a paragraph-long comment to justify why the workaround is OK, the code is wrong — fix the code

[github-actions]

This PR may be a duplicate of:

1. error printer: print the AggregateError header, label [cause]/[errors] blocks, and guard the .errors walk #36602 - Fix Support import assertions #4 in that PR addresses the exact same double source-map remapping bug in remap_zig_exception, skipping frames where remapped is already true

🤖 Generated with Claude Code

[robobun]

Closing as duplicate of #36602.