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`bun completions` formatted the bunx symlink path and the `.zshrc` line through `bstr::BStr` into fixed buffers with writers that panic. A byte that is not UTF-8 became U+FFFD, so the command used a different path. A value that did not fit aborted with `buf_print_z: buffer too small`. The `.zshrc` lookup and the completions path were written into a path buffer with no length test. The link paths, the `.zshrc` path and the `.zshrc` line are now a `strings::concat_buf_t` of raw bytes. The completions path is joined with `resolve_path::join_z_buf_checked`. A location that does not fit is skipped, like one that does not exist. `buf_print_z_infallible` has no other caller and is removed. The tests take the length limits from `MAX_PATH_BYTES`. On macOS the private executable of the bunx tests is a clone, because the realpath of a hardlink can name another link there.
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Updated 1:05 AM PT - Oct 29th, 2026
❌ @robobun, your commit 25421c8 has 6 failures in
🧪 To try this PR locally: bunx bun-pr 46423That installs a local version of the PR into your bun-46423 --bun |
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Status: fix is in this PR (#46423). Reproduction on main mkdir -p /tmp/c/empty && cd /tmp/c
cp "$(command -v bun)" ./bun && ln -s ./bun ./bunx # a bunx beside the executable, so the search goes on to $HOME
H=$(python3 -c "import sys; sys.stdout.buffer.write(b'/tmp/c/' + b'\xe9'*1400)")
env -i PATH=/tmp/c/empty HOME="$H" SHELL=/bin/zsh ./bun completions > /dev/null # PATH must have no bunx
# exit 134, panic: buf_print_z: buffer too small: ErrorWith CI on head
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No actionable comments were generated in the recent review.
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| Layer / File(s) | Summary |
|---|---|
bunx symlink paths and validation src/runtime/cli/install_completions_command.rs, test/cli/bun.test.ts |
Unix bunx installation constructs candidate paths with checked byte concatenation and skips paths that cannot be constructed. Tests cover candidate locations, maximum path boundaries, and invalid UTF-8 paths. |
Zsh completion paths and configuration src/bun_core/fmt.rs, src/bun_core/output.rs, src/runtime/cli/install_completions_command.rs, test/cli/bun.test.ts |
Zsh completion and .zshrc paths use checked byte-buffer construction. The infallible formatting helper was removed. Guidance is printed as byte segments, and print_error_bytes writes raw bytes to stderr. Tests cover path limits, hint detection, and raw-byte paths. |
Suggested reviewers: jarred-sumner, dylan-conway
Priority:
Merge Risk: 
25421
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The changes preserve raw path bytes and check completion-path limits. No concrete merge-blocking issue is established; merge after normal checks.
Pre-merge checks: 
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Check name Status Explanation Title check The title clearly summarizes the main change: building bunx link and .zshrc paths from raw bytes for completion handling. Description check The description provides detailed problem, fix, verification, background, limitations, test results, and related context. It does not use the exact template headings, but it covers the required purpos… 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: Description check
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Inline comments:
Review comments at @test/cli/bun.test.ts:
- Line 345: Update the four new bunx completion tests to use concurrent
execution: change the individual tests to test.concurrent, convert the test.each
case to test.concurrent.each, and preserve skipIf while using
test.concurrent.skipIf for the Linux-gated test. Keep each test’s existing setup
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline findings, I also checked that the restructured bunx candidate loop is byte-for-byte equivalent to the old format strings (bun_core::dirname of a root-level executable returns /, so //bunx is produced in both versions, and a trailing-slash $BUN_INSTALL still gives //bin/bunx), that concat_buf_t counts the explicit NUL so a 4095-byte link path is the longest accepted, and that buf[read..] is empty when pread_all fills the whole buffer (the /dev/zero case), which yields the hint rather than an index panic.
Extended reasoning...
The change touches only the completions installer's path construction and a dead bun_core::fmt helper, replacing panicking formatters with raw-byte concatenation that skips an over-long location; it touches no auth, crypto or injection surface. Two inline findings are posted (a pre-existing U+FFFD .zshrc line is not repaired, and the new bunx tests run serially), so the body only records the refactor-equivalence and overflow-arithmetic checks that were examined and ruled out.
Additional findings (outside the current diff — GitHub can't attach inline comments there):
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🟣
src/runtime/cli/install_completions_command.rs— Users on Linux with a non-UTF-8 $HOME who ranbun upgradeon 1.4.0-1.4.3 keep a broken .zshrc line and get no repair and no hint from this fix. Their .zshrc holds a "# bun completions" block whose path has U+FFFD bytes; the marker check at src/runtime/cli/install_completions_command.rs:503 short-circuits withbreak 'brk false, so the corrected raw-byte line is never appended and nothing is printed. The PR exists to fix exactly this population, yet for anyone who already hit the bug it is a silent no-op. Fix: when the marker is found butstrings::contains(contents, completions_path)is false, print the hint (or rewrite the stale line) so the user learns the existing line is wrong.Why this was flagged
Trigger: $HOME with a Latin-1 byte (e.g. /home/jos\xE9), zsh, a .zshrc written by 1.4.x
bun upgradecontaining "# bun completions" and a source line with EF BF BD in the path; entry through exec() :452 then :495-507. The check at :503 matches on the marker alone and breaks false, so neither the new concat at :513 nor the hint at :537 runs; stderr shows only "Installed completions to". The base behaves the same at this line, but the base also produced the broken line; this diff ships the fix for that population and leaves them in the broken state with no signal. The PR's Downsides section names a manual repair the user has no way to learn about from the tool. Population: every Linux user with a non-UTF-8 home who upgraded through 1.4.x, on every laterbun upgrade. Remedy: treat marker-present-but-path-absent as needing the hint.Verification: Pre-existing; acknowledged in diff. The trigger is Linux, zsh,
$HOMEcontaining a non-UTF-8 byte, and a.zshrcthat 1.4.0–1.4.3 populated with# bun completionsand asourceline whose path has EF BF BD. The marker-only match at src/runtime/cli/install_completions_command.rs:501-507 breaksfalse, so the hint at :537-543 is not printed. The base fails the same way by the same route.
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#46504 fixes the same One statement of that file was written differently in an earlier draft of #46504: the line that bun tells the user to add ( pretty_error!("<r>To enable completions, add this to your .zshrc:\n <b>");
Output::flush();
let _ = Output::error_writer().write_all(
&[
b"[ -s \"".as_slice(),
completions_path,
b"\" ] && source \"",
completions_path,
b"\"\n",
]
.concat(),
);For a valid path, stderr is byte-identical to main 9634520 with |
…letions-raw-byte-paths # Conflicts: # test/cli/bun.test.ts
The two "bunx symlink beside the executable" cases link to an executable whose own path is as long as a path can be. A file system can limit a symlink target to less (XFS: 1024 bytes), and symlink(2) then fails for every candidate. The cases now run only when a probe symlink with a target of that length can be made. The new bunx tests run concurrently. When the temporary directory is on another file system than the executable, they link to one shared copy.
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I reviewed the latest push and found no new bugs; the new bunx tests now run concurrently and the symlink-target probe addresses the earlier nit. Because this reworks every path the completions installer builds and the MAX_PATH_BYTES boundary tests were exercised on Linux only, a human look (plus a green macOS lane) is still worthwhile.
What was reviewed:
- The four
(dir, suffix)candidates ininstall_bunx_symlinkagainst the old format strings: byte-identical results (including//bunxfor an executable at/, and/.bun/bin/bunxfor an empty$HOME), andconcat_buf_thandsfrom_slice_with_nulexactly one trailing NUL. join_z_buf_checkedin the zsh branch wraps the samejoin_string_bufthe old code used, so normalization is unchanged; the let-chain skips only the.zshrcstep, and the "Installed completions" message still prints.- The
.zshrcline buffer (len * 4 + 96reserved vs42 + 2 * lenwritten) and the/dev/zerocase that now breaks to the hint instead of panicking;buf_print_z_infalliblehas no remaining callers. - The comment at src/runtime/cli/install_completions_command.rs:48 describes the removed formatter rather than the current code — a nit, not posted.
Extended reasoning...
The diff replaces format-based path construction in src/runtime/cli/install_completions_command.rs with raw-byte concat_buf_t/join_z_buf_checked calls so that non-UTF-8 and overlong $HOME/$BUN_INSTALL/$ZDOTDIR/executable paths are handled without U+FFFD substitution or panics, deletes the now-unused buf_print_z_infallible from src/bun_core/fmt.rs, and adds 15 tests plus shared helpers in test/cli/bun.test.ts. It touches no auth, crypto or injection surface; the sensitive part is NUL-terminated path assembly into fixed buffers, which I traced through the helpers and found bounds-checked. The latest commit (4c96e90) made the bunx tests concurrent and added a symlink-target-length probe, addressing the prior review's nit. Deferring rather than approving because the change is a non-trivial refactor of user-reachable path handling, the boundary tests were run on Linux only per the author, and no CODEOWNERS entry covers these files.
…line When `bun completions` cannot edit `.zshrc`, it prints the line for the user to add. That statement formatted the path through `bstr::BStr`. For a path that is not UTF-8 the printed line had U+FFFD where the line that bun writes to `.zshrc` has the bytes, and a copy of it in `.zshrc` was not found again. 1.3.x printed the bytes. The line now goes to stderr as bytes, through the new `Output::print_error_bytes`, the stderr twin of `print_bytes`. It uses the same writer as the text before it. A terminal in the encoding of the file name, or `2>file`, shows the bytes. A UTF-8 terminal still shows U+FFFD. For a path that is UTF-8 the output is the same bytes.
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The printed line ( It is the same line that bun writes to The mechanism is not the flush form. The reach is small, and the body says so: a run by hand under zsh with no |
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LGTM — the raw-byte path assembly is sound and the earlier nit about serial bunx tests is addressed by the move to test.concurrent.
What was reviewed:
- Every
ZStr::from_slice_with_nulinput in install_completions_command.rs comes from aconcat_buf_tcall whose last part isb"\0", andjoin_z_buf_checkedalready returns a NUL-terminatedZStr;concat_buf_trejects a slice that does not fit (s.len() > out.len() - off), so a path plus NUL of exactlyMAX_PATH_BYTESfits and one byte more is skipped, matching the test boundaries. - The
let mut completions_path_buf = ...link in theif letchain keeps thePoolGuardalive for the whole block that borrowscompletions_pathfrom it; the.zshrcline concat intobuf[read..]returnsErron an empty tail (e.g. /dev/zero), which routes to the hint instead of a panic. pretty_error!and the newOutput::print_error_bytesboth go throughprint_to/write_bytesonDestination::Stderr, so the hint bytes stay ordered;buf_print_infalliblestill has callers in RangeRequest.rs and integrity.rs, so only the truly deadbuf_print_z_infallibleis removed.- Checked the root-exe case (
dirname=/gives//bunx): same as the oldformat_args!path, no regression.
Extended reasoning...
The change rewrites the non-Windows bunx symlink search and the zsh .zshrc path/line construction in src/runtime/cli/install_completions_command.rs to use raw-byte concatenation into fixed path buffers, adds a stderr byte writer in src/bun_core/output.rs, deletes a now-unused panicking formatter in src/bun_core/fmt.rs, and adds 15 boundary and non-UTF-8 tests in test/cli/bun.test.ts. It touches no auth, crypto, or network surface; the sensitive part is fixed-buffer length handling, and each new fallible site (concat_buf_t, join_z_buf_checked) was traced to a skip or hint rather than a panic. The Rust portion is about 100 lines and self-contained, no CODEOWNERS entry covers these files, the one third-party (coderabbit) thread was resolved by a non-author, and the only prior concern from this bot (serial bunx tests) is addressed in the current code, which decided approve.
…letions-raw-byte-paths # Conflicts: # test/cli/bun.test.ts
Problem
bun completionsfails silently for a$HOMEwith one non-UTF-8 byte: no bunx symlink, and asourceline for a nonexistent path in.zshrc. 1.3.14 did both.$HOME,$BUN_INSTALL,$ZDOTDIRor executable directory too long for a path aborts:panic: buf_print_z: buffer too small: Error.install_completions_command.rsformats these paths throughbstr::BStr(U+FFFD for each invalid byte) into fixed buffers, with writers that panic.Fix
strings::concat_buf_tbuilds the link paths, the.zshrcpath and the.zshrcline from raw bytes, andjoin_z_buf_checkedthe completions path. A location that does not fit is skipped..zshrchas the same bytes (newOutput::print_error_bytes, separate commit).buf_print_z_infalliblehas no other caller and is removed.test/cli/bun.test.ts(16 new tests, 10 fail on main). Self-reviewed twice.Background
MAX_PATH_BYTESarray (4096 on Linux).concat_buf_tcopies slices into one, or fails.bun completionsalso installs thebunxsymlink and, for zsh, adds asourceline to.zshrc.bun upgraderuns it.Downsides
.zshrcwith a U+FFFD line from 1.4.x keeps it. Repair: delete the# bun completionsblock and rerun.MAX_PATH_BYTESbytes gets no.zshrcline.Notes
Provenance and reach. Found by reading the code. No user reported it and no issue exists. Crash reports were not searched. A
$HOMEthat does not fit in a path is not a real account. A home directory with a Latin-1 byte (/home/jos\xE9) is, on Linux.The printed line has a smaller reach.
bun upgradeand the install script drop the output ofbun completions. So a person sees the line only after a run by hand, under zsh, with no.zshrcor.zshenvthat opens for writing. The bytes then show in a terminal that uses the encoding of the file name, or with2>file. A UTF-8 terminal draws U+FFFD for them with and without this change. Nobody needs the printed line:echo '[ -s "$HOME/.bun/_bun" ] && source "$HOME/.bun/_bun"' >> ~/.zshrcworks on main, and bun then adds nothing. The reason for the commit is that the line has one form: bun writes it, prints it, and looks for it in.zshrc. Withbun completions <d>/comp-\xE9, a copy of the line that main prints is not found again and main appends a second block. A copy of the line that this branch prints is found.The six statements (line numbers on main
2d6d4454f3)::41-48bunx link beside the executablebuf_print_z_infallibleoverbstr::BStr<dir>/bunx:59-62bunx link in$BUN_INSTALL/bin,$HOME/.bun/bin,$HOME/.local/bin:475-484.zshrclookupindex out of bounds: the len is 4096 but the index is 4096, orrange end index 4212 out of range for slice of length 4096$ZDOTDIR/.zshrcor$HOME/.zshrcof 4096 bytes or more:460-464completions pathjoin_string_bufinto a path buffer:range end index 4096 out of range for slice of length 4095join_z_buf_checked, no.zshrcline when too long:496-522.zshrclinebuf_print_infallibleoverbstr::BStr:buf_print: buffer too small: Error.zshrcover 64 KB and a path that is mostly not UTF-8, or a.zshrcthat is longer thanfstatsaid:535-541the line, printedpretty_errorln!overbstr::BStr.zshrcOutput::print_error_bytesThe
.zshrcline reserves 4 bytes for each byte of the path. The path is printed twice, and U+FFFD is 3 bytes, so the formatted line needs up to 6.Versions (Linux x64, release builds, each row run here):
0d9b296af)367d939d9) and main$HOME=<d>/jos\xE9, zsh, no bunx on$PATH$HOME/.bun/bin/bunxmade, raw byte in.zshrcsourceline withEF BF BD$HOMEwith no.zshrc: the printed lineE9(run on 1.3.13)EF BF BDE9$HOME= 1400 bytes of0xE9buf_print_z: buffer too small<dir>/bunx$HOME/.local/bin$ZDOTDIR$HOME/.zshrcedited$HOMEor$BUN_INSTALLTests. All in
describe("completions")oftest/cli/bun.test.ts. A release build of main179664ea89fails 10 of the 16 new tests. The other 6 pass on both: they hold the value one byte below each limit, and the text of the.zshrcline.$BUN_INSTALLis skipped and$HOME/.bun/bingets the link$HOME/.local/bin/bunxatMAX_PATH_BYTES - 1bytes is made, one byte more is skippedMAX_PATH_BYTES - 1bytes, skipped at one byte more (2 tests, see the file system note below)$HOME/.local/bin, then in a$HOMEwith 1400 bytes of0xE9$ZDOTDIR/.zshrcatMAX_PATH_BYTES - 1bytes is edited, one byte more is skipped and$HOME/.zshrcis edited (2 tests)MAX_PATH_BYTES - 6,- 5and- 1bytes (3 tests).zshrc, for a directory given as an argument, with a trailing slash, and through$BUN_INSTALL(3 tests).zshrcthat is a symlink to/dev/zerogets the printed line, not an abort.zshrcas it is.zshrcis found againThe three Linux-only tests need file names that are not UTF-8, which macOS refuses. The length tests take the limit from
MAX_PATH_BYTESof the harness. Build 132948 passed on head867e2a6c24with all 181 jobs. Both Alpine lanes and both macOS lanes ran.File system note. The target of the bunx symlink is the executable's own path. In the two tests of the link beside the executable that path is as long as a path can be. A file system can limit a symlink target to less (XFS: 1024 bytes), and
symlink(2)then fails for every location. Build 130535 failed these two tests on both Alpine lanes in that way: no link in any directory. AnLD_PRELOADshim that refuses a target over 1024 bytes gives the same two failures with the same values here. The two tests now run only where a probe symlink with a target ofMAX_PATH_BYTES - 1bytes can be made. Therebun completionsmakes no bunx link for such an executable, because the kernel refuses each target.The new bunx tests run concurrently and share the helper
bunxInstaller. Where the temporary directory is on another file system than the executable, they link to one copy of it. On macOS it makes the private executable withCOPYFILE_FICLONE, not a hardlink. That is the change of #43721:fs.realpathSyncof a hardlink can name another link there, and that made the existing bunx test fail its first attempt in 36 of 400 builds. With this merged, #43721 is not needed.Cost for input that never hits this. Release builds of main
179664ea89and of this branch with the printed-line commit, same fixture paths for both. Main37a5e3a71cwas merged in after that (7e018be1d6). The merge changes none of this PR's lines insrc/.strace,perf,valgrindandbloatyare not in the container, so the counts come fromgdb..zshrc, where the line is printed: 1/11/9/2/0/2 on both. 4 fixtures,gdbcatch syscall)exec, fresh zsh install:mi_malloc5 -> 5,mi_zalloc4 -> 4,mi_realloc3 -> 3,mi_free6 -> 6. With no.zshrc: 7/3/3/7 on both (gdbbreakpoint counts).zshrc: the same 184 bytes withNO_COLOR=1and the same 204 bytes withFORCE_COLOR=1as main and 1.3.13.text-256,.rodata+0,llvm-size).InstallCompletionsCommand::execis 657 bytes smaller andconcat_buf_t::<u8>has a new out-of-line copy of 340 bytes. Alignment padding takes the rest.which()to the firstsymlinkcall: 5808 -> 5497. From the.zshrcline statement topwrite: 1019 -> 175 (gdbstepicount, 32-byte directory, two rounds each, measured atdcad5610c4against main2d6d4454f3. These statements did not change after that). The loop reads$BUN_INSTALLand$HOMEbefore the first attempt. Main read them after it failed. That is inside the 5497.<BStr as Display>::fmtcalls on path bytes on the data path: 3 -> 0 per fresh zsh install and 5 -> 0 when the search falls through to$HOME/.local/bin(gdbbreakpoint counts, debug builds, measured atdcad5610c4). The printed line had 2 more on main and has 0 now (by reading, not counted).$ZDOTDIR/.zshrcof 4095 bytes is edited and 4096 is skipped. A completions path of 4095 bytes gets its line and 4096 gets none.bun_corepublic functions: net 0 (buf_print_z_infallibleremoved with 0 references left,print_error_bytesadded with 1 caller)Inputs that work on main. Eleven inputs ran on both release builds: ASCII
$HOME,$HOMEwith a trailing slash, empty$HOME, relative$HOME,$HOME=<d>/link/..,bun completions <d>/comp/,<d>//comp,<d>/./comp,$BUN_INSTALL=<d>/link/../dir, and a$HOMEwith no.zshrcwithNO_COLOR=1and withFORCE_COLOR=1. The exit code, every bunx link, every.zshrcand the stderr bytes are the same for all eleven. Three of them print the line.Left as it is.
$BUN_INSTALL=<d>/link/../dir, wherelinkis a symlink,.zshrcnames<d>/dir/_bunand the file is in another directory. 1.3.14 used the path of the open file. A first version of this change wrote the directory as it was given. That changed the text for//and/./too, so it is not here.sourceline ofbun completions, written or printed. The messages of this file (Installed completions to ...and the error messages) still format the path throughbstr::BStr. So one run can show a path that is not UTF-8 in two forms..zshrcwhose path ends in/.bun/_bun, is accepted as done, on main and here. 1.3.13 appended a working line..zshrcline puts the path in double quotes with no escaping, as in 1.3.x.bun ./hello.jsin such a directory fails withModule not foundon 1.3.14, main and this branch. A JavaScript bin thatbun add -ginstalls under such a$HOMEruns on 1.3.13 and 1.4.2 and fails the same way on main and on this branch.export PATH=line ofbun add -g(src/install/PackageManager/updatePackageJSONAndInstall.rs:657-666) prints the bytes on 1.3.13 and U+FFFD on 1.4.2, main and this branch. Read, not run:bun patch --commit '<folder>'(src/install/PackageManager/patchPackage.rs:575-578,:1058-1065),cd <dir>ofbun create(src/runtime/cli/create_command.rs:1212-1216),bun test ./<arg>(src/runtime/cli/test_command.rs:2550-2554). They share no code with this file and no issue tracks them.bstr::BStr:src/runtime/cli/run_command.rs:3512-3520,src/runtime/cli/test/ChangedFilesFilter.rs:346-354,src/install/PackageInstall.rs:2497-2514. Append non-UTF-8 bytes instead of formatting them: run --filter output, build names, CSS module hash, shell which #46157 and pm bin, Bun.cron: append path bytes instead of formatting them #46504 cover six more.Repair of a
.zshrcfrom 1.4.x. The block is the line# bun completionsand the[ -s "..." ] && source "..."line after it. Delete both. With one of them left,bun completionstreats the file as done.Self-review. Two rounds. The first, on the whole change: 27 concerns raised, 25 addressed. Not done: a search of crash reports for these panics (no access), and a fix for
install.sh, which runs$exe completionswithout quotes (another bug, in another file). The second, on the printed-line commit: 17 concerns raised, 16 addressed. Rejected: keep that commit out until a maintainer asks for it. It is a separate commit, so it can be dropped. The head before it (4c96e90815) is green on build 132812. The hunks of #43067 are not removed on its branch, which conflicts with main. A comment there points here.Related. #45710 made the same change for the bunx cache path (
path_in_cacheinbunx_command.rs). #46021 usedconcat_buf_twith a NUL part for the snapshot paths and addedjoin_z_buf_checked. #43067 is open and has two commits for this file (1497b8df06,0057d6a6f8): they make the symlink format calls fallible, replace the.zshrccopies and deletebuf_print_z_infallible. They keep thebstr::BStrformat and leave the.zshrcline as it is. One result differs: for a completions path that does not fit, #43067 prints the line, and this change prints nothing and writes no line. #46504 (bun pm bin,Bun.cron) left this file to this PR and offered the printed line asOutput::flush()plusOutput::error_writer().write_all(...). By its own count that form makes 3write(2)calls where main makes 1, and one more allocation.print_error_byteskeeps 1 and allocates nothing.fmt::sneeds valid UTF-8 (#37422 makes it check), so the printed line does not use it.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/cli/bun.test.ts