cli: stop aborting on --cwd and --tsconfig-override values longer than the path join buffer

[robobun]

Problem

• bun --cwd <value> ... aborts at startup when the value is longer than the path join buffer, instead of printing an error:

  $ bun --cwd "/$(head -c 5000 /dev/zero | tr '\0' a)" -e 0
  panic: range end index 5000 out of range for slice of length 4095
  

  (exit 134). A relative value of the same length, and bun run / bun test with the flag, abort the same way; so does bun --tsconfig-override <value> with a value of that length.
• Cause: both flags are resolved in src/runtime/cli/Arguments.rs (parse, the --cwd block and the --tsconfig-override assignment) with resolve_path::join_abs / join_abs_string, which normalize into a fixed 4096 byte thread-local buffer (PARSER_JOIN_INPUT_BUFFER, src/paths/resolve_path.rs) with no bounds check, so a value whose normalized form does not fit panics inside the normalizer, before the syscall that would have rejected it.

Fix

• src/paths/resolve_path.rs: add join_abs_string_spill, the join_abs counterpart of the existing normalize_string_spill / join_spill: it uses the thread-local buffer when the result is known to fit and otherwise joins into a caller-provided Vec, grown as needed. The size bound it relies on (join_abs_needed) is the one JoinScratch::init and join_abs_string_buf_checked already computed inline; both now call the shared helper.
• src/runtime/cli/Arguments.rs: --cwd and --tsconfig-override resolve through join_abs_string_spill. Nothing else about either flag changes: --cwd still hands the result to chdir, which rejects anything over the OS limit itself, so an over-long value now prints the existing ENAMETOOLONG: File name too long: Could not change directory to "<value>" (chdir) and exits 1; --tsconfig-override is still stored and opened by the resolver, which already prints error: Cannot read file "<path>": ENAMETOOLONG for such a path (same as it does today for a value that happens to fit the buffer but not the OS limit), non-fatal at runtime and fatal for bun build, as for any other unreadable override.
• Why this shape: the OS (or the resolver's bounded open) is already the authority on path length for both flags, and reports the right errno, so the CLI only has to get the value there without going through a fixed buffer. Values that merely look long but normalize down (a/../a/...) keep working, which a length check on the argument would have broken; a test covers that.
• Scope: these are the two argv values that Arguments::parse itself turns into a path. Every other option parse accepts was probed with a 5000 byte value as well (--env-file, --preload / --require / --import, script and bun build entry paths, --cpu-prof-dir / --cpu-prof-name, bun test --coverage-dir, bun build --outdir / --outfile / --root / --public-path / --external, -c); the ones that still abort are in other code and each already has its own fix open, so they are intentionally left alone here:
  • -c / --config is resolved in src/bunfig/arguments.rs: bunfig: stop panicking when the config path does not fit in a path buffer #38370.
  • An absolute script, entry point or --preload path (and any absolute import / require specifier) over PATH_MAX aborts in the resolver's load_as_file (src/resolver/resolver.rs): resolver: bound load_as_file path before writing into its PathBuffer #35857.
  • bun build --external goes through the unbounded join_abs primitive itself: bun test: stop panicking on a path argument or tree entry longer than the path buffer #35863.
  • bun install / bun add parse --cwd with their own implementation in src/install/PackageManager/CommandLineArguments.rs (different joining rules and error path); a separate fix for it is in progress.
• Verified:
  • test/cli/install/bun-run.test.ts, new --cwd longer than the OS path limit block: the two over-long cases fail on the current release build with the panic above and pass with this branch; the normalizing case and the existing --cwd test pass both ways. Whole file passes (bun bd test).
  • test/cli/run/tsconfig-override.test.ts, new path longer than the OS path limit block: both cases fail on the release build and pass with this branch; whole file passes.
  • cargo test -p bun_paths resolve_path::tests: 4 new unit tests for join_abs_string_spill (fits, spills, absolute part and long cwd, long part that collapses), 8 pass.
  • By hand with the debug build: --cwd with "", /, ., .., subdir/, an absolute directory and a missing directory behave as before; --cwd values of about 4 KiB, 5 KB and 100 KB all print the ENAMETOOLONG error and exit 1; --tsconfig-override with a missing file still prints Cannot find tsconfig file and continues.

Background

• resolve_path::join_abs / join_abs_string return a slice into a per-thread 4096 byte scratch buffer; the *_string_buf variants write into a caller buffer. Neither checks that the normalized result fits, so they are only safe for inputs whose length is already bounded. The file already has normalize_string_spill and join_spill for unbounded input: use the thread-local buffer when a cheap upper bound says the result fits, otherwise a caller Vec. This PR adds the missing join_abs member of that family.
• The upper bound: _join_abs_string_buf concatenates cwd and the parts with one separator each (plus one more when a bare Windows root needs a separator appended) and then normalizes, which never makes a path longer except for the Windows cases noted on normalize_string_spill, so cwd.len() + sum(part.len() + 1) + 2 always holds both the concatenation and the output. That expression was already used in two places in the file; join_abs_needed names it.
• chdir(2) returns ENAMETOOLONG for any path at or over PATH_MAX (4096 on Linux, 1024 on macOS) or with a component over NAME_MAX; Output::err(sys_error, ...) prints it as <ERRNO>: <strerror>: <message> (<syscall>), which is the message the --cwd block already prints for any chdir failure.
• The resolver opens tsconfig_override through bun_sys::openat_a / open_a, which return ENAMETOOLONG themselves for a path that does not fit a PathBuffer, and reports it as Cannot read file "<path>": <errno>; a long value that fits the buffer gets the same message from the kernel today.

[coderabbitai]

Walkthrough

The path resolver now supports oversized absolute joins through caller-owned spill buffers. CLI --cwd and --tsconfig-override use this API. Regression tests cover oversized paths, normalization, ENAMETOOLONG, and signal-free execution.

Changes

Oversized path resolution

Layer / File(s)	Summary
Spill-capable absolute path joining src/paths/resolve_path.rs, test/...	The resolver centralizes capacity calculation and adds join_abs_string_spill. Tests cover oversized inputs, absolute parts, long working directories, and normalization.
CLI path resolution integration src/runtime/cli/Arguments.rs, test/cli/install/bun-run.test.ts, test/cli/run/tsconfig-override.test.ts	--cwd and --tsconfig-override use local spill buffers. Tests cover oversized absolute and relative paths and platform-specific ENAMETOOLONG behavior.

Possibly related PRs

• oven-sh/bun#38359: Addresses oversized path handling with spill-capable construction and ENAMETOOLONG tests.
• oven-sh/bun#38370: Applies overlong path handling to bunfig configuration loading.

Suggested reviewers: jarred-sumner, dylan-conway, cirospaciari

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the CLI flags and the fix for path values that exceed the join buffer.
Description check	✅ Passed	The description explains the problem, fix, scope, rationale, and verification steps, despite using different headings from the template.

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[robobun]

Reproduced on the current release build (Linux): bun --cwd "/$(head -c 5000 /dev/zero | tr '\0' a)" -e 0 aborts with panic: range end index 5000 out of range for slice of length 4095; a relative value of the same length, and --tsconfig-override with a value of that length, abort the same way.

With this branch --cwd prints ENAMETOOLONG: File name too long: Could not change directory to "..." (chdir) and exits 1, and --tsconfig-override prints the resolver's Cannot read file "...": ENAMETOOLONG like it does for any unreadable override. New cases in test/cli/install/bun-run.test.ts (--cwd longer than the OS path limit) and test/cli/run/tsconfig-override.test.ts (path longer than the OS path limit) fail on the release build and pass with the debug build of this branch; both files pass in full, and cargo test -p bun_paths resolve_path::tests passes with the 4 new unit tests.

Not in this PR: bun install / bun add parse --cwd in their own code (src/install/PackageManager/CommandLineArguments.rs) with a different error path; that overflow is being fixed separately.

[robobun]

^{Updated 4:05 AM PT - Aug 14th, 2026}

❌ @robobun, your commit ed5e9d0 has some failures in Build #95555 (All Failures)

---

🧪   To try this PR locally:

bunx bun-pr 38368

That installs a local version of the PR into your bun-38368 executable, so you can run:

bun-38368 --bun

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@test/cli/install/bun-run.test.ts`:
- Around line 340-356: Change the test declaration for the independent
subprocess cases to use concurrent execution, such as it.concurrent, while
preserving the existing test body and assertions.

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📥 Commits

Reviewing files that changed from the base of the PR and between f7ad274 and ed5e9d0.

📒 Files selected for processing (4)

• src/paths/resolve_path.rs
• src/runtime/cli/Arguments.rs
• test/cli/install/bun-run.test.ts
• test/cli/run/tsconfig-override.test.ts

[robobun]

Reworked in f972ed3 and ed5e9d0 in response to the reviews:

• --tsconfig-override, the other argv path resolved in Arguments::parse, had the same overflow and is fixed too (covered in test/cli/run/tsconfig-override.test.ts).
• Instead of a bounded join plus a synthesized ENAMETOOLONG at the --cwd site, resolve_path gains join_abs_string_spill (same shape as the existing normalize_string_spill / join_spill) and both flags go through it, so chdir and the resolver's open report the error themselves. The size expression the file already used in two places is now join_abs_needed, with unit tests for the new function.
• bun install / bun add --cwd (src/install/PackageManager/CommandLineArguments.rs) is a separate parser with its own joining rules and error path; it has the same kind of overflow and is being fixed separately, so this PR leaves it alone. The description now says so.
• The call-site comments are gone; what is left are the doc comments on the two new functions, in the same form as the neighbouring *_spill functions' docs.
• On it.concurrent for the new --cwd cases: the whole file sits under describe.concurrent("bun run", ...), which also applies to tests in nested describe blocks (three 300 ms tests in such a block finish in about 300 ms total), so the new cases already run concurrently like the rest of the file. The --tsconfig-override block uses an explicit describe.concurrent because its parent is a plain describe.

[claude]

Additional findings (outside current diff — PR may have been updated during review):

• 🔴 src/runtime/cli/Arguments.rs:971-980 — A third same-class sibling is left unfixed and unmentioned: the -c/--config handler at src/bunfig/arguments.rs:191-217, called via load_config_with_cmd_args at line 924 of this file (between the two hunks this PR modifies). Its absolute branch does config_buf[..config_path_.len()].copy_from_slice(config_path_) into a PathBuffer and its relative branch uses the unchecked join_abs_string_buf, so bun -c="/$(head -c 5000 /dev/zero | tr '\\0' a)" -e 0 still aborts with the exact range-index panic this PR eliminates (and on macOS a mere 1025-byte value trips it, since PathBuffer is 1024 there). Per REVIEW.md's whole-class rule — which this PR already accepted last round by fixing --tsconfig-override and explicitly excluding install --cwd — this needs the same join_abs_string_spill treatment (the downstream load_config_path → report_bunfig_load_failure path already surfaces the open failure cleanly), or an explicit exclusion in the description alongside install --cwd.

  Extended reasoning...

  What the bug is

  The previous review round flagged two sibling sites with the identical "unbounded argv → fixed path buffer → range-index panic" pattern; the second commit fixed --tsconfig-override and the PR description now explicitly excludes install --cwd as tracked separately. A third sibling on the same Arguments::parse() call path is neither fixed nor mentioned: the -c/--config handler at src/bunfig/arguments.rs:154-221, reached via load_config_with_cmd_args(cmd, &args, ctx) at src/runtime/cli/Arguments.rs:924 — literally between the --cwd hunk (~840) and the --tsconfig-override hunk (~971) this PR modifies.

  The specific code path

  load_config_with_cmd_args (line 234 of src/bunfig/arguments.rs) forwards args.option(b"--config") — the raw unbounded argv slice — to load_config. command::LOADS_CONFIG[cmd] gates the call at Arguments.rs:923, but AutoCommand/RunCommand are in that set, so bun -e / bun run reach it. Inside load_config:

  • Line 154: let mut config_buf = PathBuffer::uninit(); — a [u8; MAX_PATH_BYTES], which is 4096 on Linux and 1024 on macOS.
  • Line 167: config_path_ = user_config_path_.unwrap_or(b"") — the raw --config value.
  • Absolute branch (191-194): if config_path_[0] == b'/' { config_buf[..config_path_.len()].copy_from_slice(config_path_); config_buf[config_path_.len()] = 0; } — no length check before the slice index.
  • Relative branch (210-217): resolve_path::join_abs_string_buf::<platform::Auto>(awd, &mut *config_buf, &parts) then config_buf[config_path_len] = 0 — the unchecked join_abs_string_buf variant writing into a fixed PathBuffer, the exact shape this PR replaced with join_abs_string_spill for --cwd and --tsconfig-override.

  Step-by-step proof

  Take bun -c="/$(head -c 5000 /dev/zero | tr '\0' a)" -e 0 on Linux:

  1. args.option(b"--config") returns Some(&[u8]) of length 5001 (leading / + 5000 as). -c/--config is in SHARED_PUBLIC_PARAMS, so every subcommand that reaches parse() accepts it.
  2. LOADS_CONFIG[AutoCommand] is true, so line 924 calls load_config_with_cmd_args, which calls load_config(cmd, Some(<5001 bytes>), ctx).
  3. user_config_path_.is_none() is false, so the standalone-graph early return is skipped. config_path_ = the 5001-byte slice; it is non-empty so line 187's early return is skipped.
  4. config_path_[0] == b'/' is true → absolute branch at line 192: config_buf[..5001] on a [u8; 4096] panics with range end index 5001 out of range for slice of length 4096.
  5. Process aborts with exit 134 — the exact panic string and exit code this PR's description quotes for the case it fixes.

  On macOS the threshold is 1025 bytes rather than 5001, since MAX_PATH_BYTES = 1024 there; the relative branch panics identically inside join_abs_string_buf's buffer write when awd.len() + config_path_.len() overflows 1024/4096.

  Why existing code doesn't prevent it

  No length check exists before either write. PathBuffer is fixed-size; args.option(b"--config") returns raw argv with no bound; neither branch uses the checked/spilling variants this PR introduces.

  Why this belongs to this PR

  REVIEW.md, "Correctness: the bug class, not the bug": "Fix the whole class in the same PR (same-class sites are ONE concern, not scope creep). Grep for every sibling site sharing the pattern… If a site is intentionally excluded, say so in the PR." The author has already accepted this rule for this exact class: after the previous round's comment, --tsconfig-override was fixed with the same join_abs_string_spill and install --cwd was explicitly excluded in the description with a reason. -c/--config sits on the same parse() call path between those two hunks, matches the pattern byte-for-byte, and is neither fixed nor mentioned.

  How to fix

  Same treatment as the two hunks in this PR: replace the absolute branch's copy_from_slice and the relative branch's join_abs_string_buf with a single resolve_path::join_abs_string_spill::<platform::Auto>(awd, &mut spill, &[config_path_]) (or the checked-into-config_buf variant if the NUL-terminated ZStr shape is easier to keep). The over-long path then reaches load_config_path, whose bun_sys open returns ENAMETOOLONG, and report_bunfig_load_failure prints it cleanly — exactly as --tsconfig-override now surfaces its failure through the resolver. Alternatively, list it alongside install --cwd in the description with a reason.

[robobun]

On -c / --config: agreed that it has the same kind of overflow, but it is resolved in src/bunfig/arguments.rs, not in Arguments::parse, and #38370 already fixes it, so it stays out of this PR. I went through every option parse accepts with a 5000 byte value; the description now lists the ones that still abort and the open fix each belongs to (-c: #38370, absolute specifiers in the resolver's load_as_file: #35857, bun build --external: #35863, bun install --cwd: separate fix in progress). Everything else already reports an error.

[claude]

LGTM — the follow-up commits addressed the earlier feedback (--tsconfig-override now goes through the same spill path, and the long doc comments were trimmed to match the neighbouring *_spill docs). The bun install --cwd sibling is explicitly scoped out with a stated reason in the description, which is fine per REVIEW.md.

Checked that join_abs_string_spill is a straight instance of the existing normalize_string_spill/join_spill/join_z_spill pattern in the same file, and that join_abs_needed is byte-identical to the two inline expressions it replaces. The --cwd swap (join_abs → join_abs_string_spill with a single-part slice) and the --tsconfig-override swap preserve the previous semantics exactly, and both are covered by integration tests that assert signalCode === null plus the specific error text.

Extended reasoning...

Overview

Fixes a panic-on-argv abort: bun --cwd <5000-byte value> and bun --tsconfig-override <5000-byte value> used to hit a range-index panic inside resolve_path::join_abs*'s fixed 4096-byte thread-local buffer. The fix adds join_abs_string_spill (the missing member of the file's existing *_spill family — normalize_string_spill, join_spill, join_z_spill, join_z_buf_spill are already there with the identical shape) and routes both flags through it, so an over-long value reaches chdir/the resolver's open and gets the normal ENAMETOOLONG error instead of aborting. The size-bound expression that two call sites already computed inline is extracted as join_abs_needed.

Security risks

None. This is CLI argv → path normalization → syscall. The change moves an unbounded argv value from a fixed buffer (panic) to a spilling buffer (syscall reports the errno). No new trust boundary, no path-traversal surface change (normalization is unchanged), no external input beyond argv.

Level of scrutiny

Medium. resolve_path.rs is a shared utility, so a new public function there deserves a look — but the new function is a fifth instance of a pattern the file already has four of, down to the doc-comment wording, and join_abs_needed is a pure extraction of an expression that was already duplicated at JoinScratch::init and join_abs_string_buf_checked. The two Arguments.rs call-site changes are one-for-one swaps that preserve the platform generic and the downstream ZBox::from_bytes / Box::from ownership.

Other factors

• I reviewed this PR twice previously. The first review flagged two siblings; --tsconfig-override was fixed in f972ed3, and the author declined bun install --cwd with a stated reason (separate parser, different joining/error path, being fixed separately) that the PR description now records — REVIEW.md accepts explicit exclusion with a reason.
• The comment-cop bot's four long-comment flags were addressed by ed5e9d0 (docs now match the neighbouring *_spill functions verbatim); the two remaining bot comments at 06:05 predate that commit.
• CodeRabbit's it.concurrent nit was answered: the block sits under describe.concurrent("bun run", ...), which already makes the nested tests concurrent.
• Test coverage is solid: 4 unit tests for the new function (fits / spills / absolute-part-and-long-cwd / long-part-that-collapses), plus integration tests for both flags asserting the specific error text, signalCode === null, and the correct exit code, plus a positive case proving a value that only looks long but normalizes down still works. The description records that the new tests fail on the release build and pass on this branch.