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…:test and Bun.inspect The bun:test value formatter and the console formatter sent a key stored as Latin-1 through the JSON string escaper, and wrote a key stored as UTF-16 raw. A quote, a backslash, or a control character in a UTF-16 key was not escaped. JSC can store an ASCII-only string as UTF-16, so two equal keys could print differently. Both formatters now send both forms through the same escaper over the UTF-8 form of the key. The output for a Latin-1 key does not change.
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Included review availability: Your plan provides up to 10 included reviews per hour; 1 remains after this review. WalkthroughThe change removes UTF-16-specific helpers, uses generic UTF-16 searching for Windows argument quoting, and unifies property-key escaping through UTF-8 JSON formatting. Snapshot and inspection tests cover special characters and multiple string encodings. ChangesString formatting cleanup
Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to The added tests cover the intended escaping cases without introducing an identified merge-blocking risk. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Status: the fix is pushed and the new tests pass on a debug ASAN build. How I reproduced it on 1.4.3-canary.1+4ff919377: import { test, expect } from "bun:test";
test("keys", () => {
// The text k"a with 16-bit storage.
const wide = new TextDecoder("utf-16le").decode(new Uint16Array([0x6b, 0x22, 0x61]));
expect({ [wide]: 1 }).toMatchInlineSnapshot(); // writes "k"a": 1,
expect({ ['k"b']: 1 }).toMatchInlineSnapshot(); // writes "k\"b": 1,
});
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LGTM — collapsing the is_16bit() branch into format_json_string_utf8(&key.to_utf8(), ..) routes both storage widths through the same write_pre_quoted_string, and the Latin-1 path is output-preserving.
What was reviewed:
- Confirmed
format_json_string_latin1andformat_json_string_utf8both bottom out inwrite_pre_quoted_stringwith only the input encoding differing, so Latin-1 keys (transcoded viato_utf8()) print byte-identically to before; ASCII keys still borrow with no allocation. - Both twin sites (
ConsoleObject.rs,pretty_format.rs) fixed; bothwrite_16_bithelpers had no remaining callers and are deleted. - Tests cover the encoding matrix (forced-UTF-16 ASCII, Latin-1, BMP, supplementary) across
Bun.inspect,toMatchInlineSnapshot, and bothtoEqual/toBefailure-message paths.
Extended reasoning...
Overview
This PR removes the key.is_16bit() special-case in the two object-key printers — write_property_key in src/jsc/ConsoleObject.rs and the property-key arm of src/runtime/test_runner/pretty_format.rs — and routes every non-identifier key through format_json_string_utf8(&key.to_utf8(), Default::default()). The two now-orphaned write_16_bit helpers are deleted (grep confirms no remaining callers). Net native change is about −40 lines. New inline-snapshot tests in test/js/bun/util/inspect.test.js and test/js/bun/test/snapshot-tests/bun-snapshots.test.ts exercise the same set of special characters (", \, \n, \x1b) across four storage/codepoint classes and across the three consumer paths (Bun.inspect, toMatchInlineSnapshot, toEqual/toBe failure messages).
Security risks
None. This is diagnostic output formatting for console.log/Bun.inspect and test-runner snapshot/diff rendering. No parsing of untrusted input, no auth/crypto/permission surface, no allocation sizing driven by adversarial data beyond the same key-length transcode that already happened elsewhere.
Level of scrutiny
Moderate for correctness, low for blast radius. I traced both the old and new call paths into bun_core::fmt: format_json_string_latin1 and format_json_string_utf8 (with default quote: true) both call js_printer::write_json_string → write_pre_quoted_string, differing only in the Encoding argument. EncodedSlice::to_utf8() borrows for ASCII, transcodes Latin-1 high bytes and UTF-16 to UTF-8, so the escaper sees the same code points either way and Latin-1 output is preserved byte-for-byte. The Utf8Bytes temporary lives for the enclosing writer.print(format_args!(...)) statement, so the borrow into JSONFormatterUTF8 is sound. add_for_new_line(key.len + 2) was already an approximation (it never accounted for escape expansion) and feeds only the line-wrap heuristic, so reusing it for the merged branch is fine.
Other factors
The change follows the REVIEW.md checklist closely: both copy-pasted sites are fixed together, the dead helpers are removed in the same PR, escaping is done through the shared helper rather than a per-site loop, and the tests hit non-ASCII beyond emoji plus the forced-UTF-16-ASCII case that motivated the fix. The PR description explicitly names the two sibling sites intentionally left for follow-ups (the String object arm and string values) with issue references. No CODEOWNERS entry covers the touched files, and the bug hunt exited on dry_streak with no findings.
The console key printer was its last caller outside Windows-only code. The two Windows callers now call index_of_any_t, which it wrapped.
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Inline comments:
In `@src/jsc/ConsoleObject.rs`:
- Line 2976: Update the key conversion in the formatter call within
ConsoleObject to preserve unpaired UTF-16 surrogates instead of replacing them
with U+FFFD, while keeping the existing JSON formatting behavior. Add regression
assertions covering unpaired-surrogate property keys in both affected formatter
paths, including the corresponding test location in
src/runtime/test_runner/pretty_format.rs at lines 961-961.
In `@test/js/bun/test/snapshot-tests/bun-snapshots.test.ts`:
- Line 39: Extend the special escape-character test vector with U+2028, U+2029,
and U+FEFF in test/js/bun/test/snapshot-tests/bun-snapshots.test.ts at lines
39-39, covering both snapshot and matcher-error paths; make the same vector
extension in test/js/bun/util/inspect.test.js at lines 166-166 for Bun.inspect.
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src/bun_core/string/immutable.rssrc/jsc/ConsoleObject.rssrc/runtime/cli/run_command.rssrc/runtime/test_runner/pretty_format.rstest/js/bun/test/snapshot-tests/bun-snapshots.test.tstest/js/bun/util/inspect.test.js
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- src/bun_core/string/immutable.rs
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Updated 4:36 AM PT - Sep 11th, 2026
✅ @robobun, your commit fe60f18e6200430be7244c1c8234905dcada4fc6 passed in 🧪 To try this PR locally: bunx bun-pr 42299That installs a local version of the PR into your bun-42299 --bun |
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Closing in favor of #42320, which now carries this change together with the console printer fix, so the key escaping is defined in one place. Both PRs rewrote the same
CI on the consolidated head of #42320 is green (build #114647, and the #42298 (the |
1 participant
Problem
bun:testandBun.inspectescape an object key in two ways, by how JSC stores the key string. A Latin-1 key goes through the JSON string escaper. A UTF-16 key is written raw:",\, and control characters stay as-is.TextDecoder("utf-16le"). So two equal keys can print as"k\"a": 1and"k"a": 1.key.is_16bit()branch in both copies of the key printer:src/runtime/test_runner/pretty_format.rs:970andwrite_property_key(src/jsc/ConsoleObject.rs:2983).Fix
format_json_string_utf8(&key.to_utf8(), ..): one escaper over the UTF-8 form. Latin-1 key output does not change.",\, a control character, U+2028, U+2029, or U+FEFF.bun test -uupdates it. Fix 23382 (unicode object key printed as 'key" in snapshot instead of "key") #23390 set the precedent.test/js/bun/test/snapshot-tests/bun-snapshots.test.tsandtest/js/bun/util/inspect.test.jsfail on 1.4.3-canary. Also ranexpect.test.jsand the console tests.toBeandBun.inspectprint with it. Excluded: theStringobject printer (bun:test: a String object with 16-bit storage prints wrong characters in diffs and snapshots #42296) and string values.Background
pretty_format.rsprintstoEqualdiffs and snapshots.ConsoleObject.rsprintsconsole.log,Bun.inspect, and theReceived:value of other matchers such astoBe.write_pre_quoted_string,src/bun_core/string/mod.rs) writes\",\\,\n, and\uXXXX.Notes
No user reported this. A code read found it. The closest report is #23382 (a UTF-16 key printed as
key"), fixed in #23390 on the same branch ofpretty_format.Repro on 1.4.3-canary.1+4ff919377:
The repro builds the key from char codes on purpose. A property key is an atom. If the same text is already an 8-bit atom (for example a string literal with that text is in the file), JSC uses that atom for the key and the output is the escaped form. So before this PR the output also depended on which form of a text became a key first.
Why both printers: with only
pretty_format.rsfixed, one failing test run shows the same UTF-16 key escaped in atoEqualdiff and raw in atoBemessage. Today both are raw, so a fix to one file makes bun:test less consistent.History: keys always went through
JSPrinter.formatJSONStringuntil fd4a210 (2022, a non-ASCII fix forconsole.log). That commit added the 16-bit branch as a raw write.pretty_formatis a fork of that formatter (4792abd) and kept the split. So the JSON escaper is the original behavior for a quoted key.Direction: Jest's
pretty-formatescapes only"and\in keys, and Jest 29 snapshots escape nothing. Bun's Latin-1 path has JSON-escaped keys from the start, and most keys are Latin-1. This PR keeps that output and moves the less common UTF-16 case to it. The other direction changes the stored snapshots of each user that has a Latin-1 key with a backslash (for example a Windows path). Parity with Jest for keys is a separate question (#40656 is the open report for string values).The escape runs over
to_utf8()and not over the UTF-16 mode of the escaper. That mode works per code unit and prints an emoji as two\uXXXXescapes.The escaper also writes
\u2028,\u2029, and\uFEFFfor those three characters. A Latin-1 string cannot hold them, so this does not make the two forms disagree. A lone surrogate still prints as U+FFFD, as before (to_utf8replaces it).#36615 changes which strings get 16-bit storage (UTF-8 decode of text in the Latin-1 range becomes 8-bit). Before this PR that change moves such keys from the raw form to the escaped form. After this PR the storage width does not matter.
Sites that this PR does not change:
Stringobject arm ofpretty_format.rsreads a 16-bit string through the 8-bit view. It prints wrong characters in release and panics in debug. That is a different defect: bun:test: a String object with 16-bit storage prints wrong characters in diffs and snapshots #42296.pretty_format.rsprints them raw in both forms. The console printer sends a 16-bit value throughJSON.stringifyand an 8-bit value through the JSON escaper, so the hex case of\uescapes differs (uppercase from the JSON escaper, lowercase fromJSON.stringify).Each file had a
write_16_bithelper with no other caller. The PR removes both.index_of_any16(src/bun_core/string/immutable.rs) lost its last caller outside Windows-only code, and themordantlint reported it as an unused public function. The PR removes it. It was a one-line wrapper forindex_of_any_t. The two Windows callers insrc/runtime/cli/run_command.rsnow callindex_of_any_t.cargo check -p bun_runtime --target x86_64-pc-windows-msvcpasses.test/js/bun/test/pretty-format-overflow.test.tsexits with 139 on a debug ASAN build with and without this change (500 levels of nesting).no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/util/inspect.test.js