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WalkthroughThe parser now compares property keys by string value during object-property folding. It also preserves template-tag receiver behavior during folding and single-use substitution. Regression tests cover emitted code and runtime results. ChangesParser semantics
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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Check skipped because no linked issues were found for this pull request. |
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The description clearly explains the bug, fix, scope, downsides, cache-version impact, and verification results. It does not use the template headings exactly, but it provides the required information… |
| Title check | |
The title clearly identifies both primary changes: using EString::eql_bytes for the property fold and preserving this for template tags. |
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Updated 8:01 AM PT - Oct 15th, 2026
✅ @robobun, your commit f253f1e73d600058e4dd1bcf8ae704afe22fde38 passed in 🧪 To try this PR locally: bunx bun-pr 32297That installs a local version of the PR into your bun-32297 --bun |
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LGTM — one-line fix that brings the local shim in line with the canonical EString::eql_bytes, with a solid regression test.
Extended reasoning...
Overview
This PR fixes a UTF-16/UTF-8 string comparison bug in the e_string_eql_bytes shim in src/js_parser/fold.rs. The old code widened each UTF-8 byte to u16 and compared element-wise against UTF-16 code units, which is semantically wrong (e.g. é as UTF-8 bytes [0xC3, 0xA9] would falsely match the two-char string é whose UTF-16 code units are [0x00C3, 0x00A9]). The fix replaces the hand-rolled loop with bun_core::strings::utf16_eql_string, which is exactly what the canonical EString::eql_bytes in src/ast/e.rs:1499-1505 already does — the file header comment notes this shim only exists because of an E0034 ambiguity in the duplicated impl EString blocks.
Security risks
None. This is a minifier constant-folding correctness fix with no auth, crypto, or I/O implications. The only behavioral effect is whether ({key: v}).name folds to v under --minify-syntax; the fix makes folding strictly more conservative for the false-positive case and correctly enables it for the previously-missed true-positive case.
Level of scrutiny
Low-to-moderate. The diff is a one-line substitution that aligns a temporary shim with the reference implementation it was meant to mirror, using a helper already used for the identical purpose in src/ast/e.rs and src/js_printer/lib.rs. The single call site (maybe_rewrite_property_access → EObject arm) is narrow and gated behind minify_syntax + single-property + no-flags + non-__proto__.
Other factors
The added minify/InlineSingleObjectPropertyNonAscii test covers both failure modes (miscompile and missed fold) plus ASCII/literal-non-ASCII baselines, asserting both bundle-output shape and runtime stdout. No CODEOWNERS for these paths, no outstanding reviewer comments, and the bug hunting system found nothing.
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LGTM — brings the UTF-16 branch of the local e_string_eql_bytes shim in line with the canonical EString::eql_bytes (src/ast/e.rs:1503), with a test that covers both the false-positive and false-negative cases.
Extended reasoning...
Overview
This PR fixes a 2-line bug in src/js_parser/fold.rs's local e_string_eql_bytes shim. The old UTF-16 branch compared by widening each UTF-8 byte of the property name to u16 and matching against UTF-16 code units element-wise — semantically wrong for any non-ASCII codepoint. The fix swaps in bun_core::strings::utf16_eql_string, which is exactly what the canonical EString::eql_bytes at src/ast/e.rs:1499-1505 already does (the comment block at the top of the shim explains why this file can't call that method directly due to E0034 ambiguity from duplicate impl EString blocks). A new bundler test (minify/InlineSingleObjectPropertyNonAscii) covers the miscompile case (é vs é collision), the missed-fold case (\u00e9 vs literal é), and ASCII/literal baselines, asserting both the bundle output shape and runtime stdout.
Security risks
None. This is a pure string-equality correctness fix in a constant-folding optimization path. No auth, crypto, permissions, filesystem, or network surface is touched.
Level of scrutiny
Low. The change is a one-line substitution that makes a temporary shim byte-for-byte equivalent to the established canonical implementation elsewhere in the same codebase. The only caller is the single-property object inlining optimization (({k:v}).k → v) under --minify-syntax, which is already heavily gated (single property, no flags, not a delete/call/assign target). The PR description includes a clear repro showing the miscompile against Node, and the fix is the obvious correct one.
Other factors
The new test is well-constructed: it checks that the mismatched key's value (4097) remains inside an object literal (not folded), that the matching keys' values do fold (no : 8194 etc. in output), and that runtime evaluation produces [null,8194,12291,16388]. The PR notes the full bundler_minify.test.ts and bundler_string.test.ts suites pass. There are no prior human review comments to address. The robobun CI comment shows failures on the first commit, but a ci: retrigger commit was pushed afterward — likely flaky/infra, and unrelated to this 2-line change which only narrows behavior to match the reference implementation.
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Status: this PR was reworked on 2026-10-11. Main is merged in as of 2026-10-15 (f253f1e). The PR body describes the current shape. How I reproduced the bug: // t.js
console.log(({ "\u00c3\u00a9": 1 }).é);
PR: #32297 |
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Stale PR review: keep open, rework. The bug is real and still on main, and it is not limited to The diff is not the right shape yet. After the change, |
The local e_string_eql_bytes helper in fold.rs widened each UTF-8 byte of
the property name to u16 and compared element-wise against the UTF-16 key.
This diverges from the Zig reference (EString.eql -> strings.utf16EqlString)
and causes two problems under --minify-syntax:
({"\u00c3\u00a9": 42}).é wrongly folds to 42 (key is "é", accessor is "é")
({"\u00e9": 42}).é fails to fold (key [0x00E9] vs bytes [0xC3,0xA9])
Use bun_core::strings::utf16_eql_string for the UTF-16 branch, matching
EString::eql_bytes in ast/e.rs and the original Zig behavior.
The fold compared a UTF-16 key with the UTF-8 name through a helper that was local to fold.rs. The helper is deleted and the fold calls EString::eql_bytes, which the rest of the parser already uses. The fold now skips a template tag, because a tagged template passes the object as `this`. esbuild has the same gate on this fold. The runtime transpiler cache version goes from 34 to 35. Releases 1.4.0 to 1.4.3 wrote the wrong output into the cache. The tests cover the printed output of Bun.Transpiler, a file that bun runs, and a bundle built with minify.syntax.
A single-use local that holds a property access was substituted into the
tag of a tagged template: `const t = o.f; return t`x`` became `o.f`x``.
The tag then received `o` as `this`, and `a?.f`x`` is a SyntaxError.
The call-target arm already refuses this substitution. The template arm
now does the same.
With the template-tag gate in the `{k: v}.k` fold, this also keeps
`const o = { f: h }; const t = o.f; return !t`x`` from a call with the
object literal as `this`.
The test for a define-injected index keeps only the row that must not
fold.
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robobun
changed the title
this for template tags
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Actionable comments posted: 1
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Inline comments:
Review comments at @test/bundler/transpiler/transpiler.test.js:
- Line 286: Update both independent subprocess tests, including the template-tag
test, to use it.concurrent instead of it; leave their test bodies unchanged.
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📒 Files selected for processing (5)
src/js_parser/fold.rssrc/js_parser/p.rssrc/jsc/RuntimeTranspilerCache.rstest/bundler/bundler_minify.test.tstest/bundler/transpiler/transpiler.test.js
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main took RuntimeTranspilerCache version 35 (#45290). This branch takes 36.
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LGTM after the merge with main; nothing new turned up on this version.
What was reviewed:
EString::eql_bytesat src/ast/e.rs:1773 routes UTF-16 keys throughutf16_eql_string(src/bun_core/string/immutable.rs:2396), which decodes code points and compares WTF-8 bytes, so the Latin-1 "twin" key no longer matches the UTF-8 accessor name.- The new ETemplate guard in src/js_parser/p.rs:3238 is a line-for-line twin of the existing ECall guard (p.rs:3150), using the same
break 'outerpath. EXPECTED_VERSIONis 36 in src/jsc/RuntimeTranspilerCache.rs:69 against 35 on the base commit, so the bump is base+1 (the PR description's "35" is stale, the code is right).- Tests spawn the runtime for both the fold and the
this-of-tag cases and drain stdout/stderr/exited together.
Extended reasoning...
The diff touches the ({k: v}).k constant fold in src/js_parser/fold.rs, the single-use-symbol substitution's tagged-template arm in src/js_parser/p.rs, and the runtime transpiler cache version, plus tests in two existing bundler test files. No security-sensitive surface is involved; it is a minifier correctness fix. The source change is about 40 lines, replaces a hand-rolled comparator with the existing encoding-aware helper, mirrors an existing sibling guard verbatim, and the cache version was verified to be base+1 after the merge. The bug hunt ran dry with no findings, no CODEOWNERS entry covers the changed paths, and the only still-open thread from earlier runs is a style nit about two remaining shim helpers.
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#46915 changes the same key compare in |
Problem
bun file.jsevaluates({ "é": 1 }).éto1, notundefined(node, Bun 1.3.14). Wrong from 1.4.0 to 1.4.3. A fuzzer found it, no user did.({ k: v }).kinline compared the key's UTF-16 code units with the name's UTF-8 bytes one to one (e_string_eql_bytes,src/js_parser/fold.rs:40).éis C3 A9 in UTF-8.Fix
EString::eql_bytes(src/ast/e.rs), which compares code points, as esbuild and Bun 1.3.14 do. The helper is deleted.this: the fold skips a tag (as esbuild), and single-use substitution does not move a property access into a tag (src/js_parser/p.rs).test/bundler/transpiler/transpiler.test.js, 2 intest/bundler/bundler_minify.test.ts. All fail on main.Background
EStringis the AST string node: UTF-8 bytes, or UTF-16 when the literal has a non-ASCII character. A.nameis UTF-8.minify_syntaxon and caches output for files of 4 KiB or more.bun pm diffuses the same fold.Downsides
({ "é": () => {} }).é.nameis"", not"é", as for ASCII keys and in 1.3.14 (js_parser: do not fold{ f: () => {} }.fto the bare function #42585).!(0, o.f)`x`with a single-use one-property literalopasses the object asthis, as for every othero(Bun bindsthisfor an unbound tagged-template call #44578).Notes
How it was found, and who it reaches
undefined, so a working program does not write it.bun file.js,bun -e,bun test, Workers,new Bun.Transpiler({ target: "bun" }),bun build --minify-syntax,Bun.build({ minify }), andbun pm diff.--inspectandbun test --coverageturnminify_syntaxoff.bun pm diffon 1.4.0 to 1.4.3 called the editconst allowed = 1toconst allowed = ({ "\u00c3\u00a9": 1 }).éformatting only. With this PR it is+1 -1. The patch text of--jsonand piped output was always correct.What the template-tag part changes
({ f: h }).f`x`callshwith the object asthis. main printedh`x`. Bun 1.3.x and 1.4.x were both wrong for ASCII keys. Non-ASCII string keys were right on 1.4.x only because the compare never matched.const t = o.f; return t`x`callstwiththisundefined. main printedo.f`x`.const t = a?.f; return t`x`printeda?.f`x`, which is a SyntaxError ("Cannot use tagged templates in an optional chain").thisfor an unbound tagged-template call #44578. Rows 3 and 4 of that issue ((0, o.tag)`x`) are the comma fold insrc/js_parser/visit/visit_binary.rsand are not changed here.!(0, o.f)`x`with a single-use literal.Measurements (release builds of main 6c1eb06 and this PR, same host bun. Taken before the merge of main on 2026-10-15, when the cache bump was 34 to 35. Not measured again: in this PR's diff, that merge changes only the version number.)
.text: 65,818,853 B in both builds (llvm-size). Alignment padding absorbs the difference. Strippedbun: 89,318,984 B in both.e_string_eql_bytes(90 B) removed.substitute_single_use_symbol_in_expr3,018 B to 3,057 B.maybe_rewrite_property_access6,447 B / 6,633 B, unchanged: two instructions differ (testb $0x10is nowtestb $0x30, and the call target).stepifrom the call to its return. valgrind (callgrind, dhat) and perf are not available in the container.src/js,packages,test,benchthroughnew Bun.Transpiler({ target: "bun" }), sha256 per output): 1 file changes. It is vite 6.2.3, whereconst html = String.raw; return html...is no longer rewritten toString.raw...``. The key compare is reached 18 times, 0 with a UTF-16 key. The gate line is reached 24 times, 0 as a template tag.openat, +2close, -2pread64, +1 each offallocate,pwritev,renameat,unlink. Second run: 0. Counted with a ptrace syscall counter, because strace is not available.console.log(1);. This build (f253f1e, version 36) reportsStaleCachefor it and printsundefined. It does the same when the entry is relabelled 35. Relabelled 36, this build restores the entry and prints1. This run used the debug build, with the entry renamed to.debug.pileandBUN_DEBUG_ENABLE_RESTORE_FROM_TRANSPILER_CACHE=1. Release builds gave the same result before the merge (version 34 cached, 35 expected).[o.m][0]`x`). Keepthisundefined for call targets and template tags that a rewrite turned into a property access #40829 covers them..nameof an anonymous function or class under a non-ASCII string key. The 17 rows left are all.namerows, and 6 of them are wrong on main for identifier and ASCII keys. Bun 1.3.13 gives the same 17.Cache version:
EXPECTED_VERSIONmust be the value on main plus 1 at merge. #45290 took 35 on main, so this PR takes 36 since the merge of main (f253f1e). Other open PRs also take the next number. Git reports that conflict on the doc line only. The constant merges clean and must still go up by one.Not in this PR
e_string_init(7 call sites) ande_string_javascript_length(1 call site) stay. They are equivalent to theEStringmethods. Store non-ASCII define, env, macro and inlined path strings as UTF-16 so they fold like literals #42019 replaces 6 of the 7e_string_initsites and js_parser: do not fold .length of a folded string with a non-ascii segment #38989 removes the other helper.--definestring is still an 8-bit string:K[0]and(K + "b").lengthfold wrong. Store non-ASCII define, env, macro and inlined path strings as UTF-16 so they fold like literals #42019 and js_parser: do not fold .length of a folded string with a non-ascii segment #38989 cover that. For the same reason the tests do not pin the fold of a define-injected index that is a true match.src/js_parser/visit/visit_expr.rs:1749: a decorated anonymous class under a UTF-16 key gets the name"". js_parser: name lowered anonymous classes after numeric, non-ASCII and private property keys #38787 covers it.thisfor a template tag (comma,&&,||,??, the ternary,[x][0], import items): Keepthisundefined for call targets and template tags that a rewrite turned into a property access #40829, and Bun bindsthisfor an unbound tagged-template call #44578 for the comma rows.push_unitsinsrc/react_compiler/optimization/constant_propagation.rswidens UTF-8 bytes to UTF-16 units in the same way ("中" + Kunder--react-compiler). It has no PR yet.src/js_parser/parse/parse_typescript.rs:897: a stale E0034 comment.src/parsers/yaml.rs:1638: swapped receivers in a branch that no input reaches.({ "é-x": 3 })["é-x"]stays unfolded, as in 1.3.14.--compilebinary that an older bun built with a minify flag keeps the folded constant until it is built again.Other open PRs on these lines: #36599 has two more callers of the deleted helper and must call
.eql_bytes. #40829 and #36599 add the same template-tag line infold.rs. #38989 edits the same header comment.Suites run with the debug build:
test/bundler/transpiler/transpiler.test.js,test/bundler/bundler_minify.test.ts,test/bundler/bundler_string.test.ts,test/bundler/bundler_edgecase.test.ts,test/bundler/bundler_cjs.test.ts,test/bundler/esbuild/{dce,default,ts}.test.ts,test/bundler/transpiler/{property,runtime-transpiler,template-literal}.test.ts,test/cli/run/transpiler-cache.test.ts,test/regression/issue/{28159,30887}.test.ts. After the merge of main (f253f1e):transpiler.test.js(245 pass),bundler_minify.test.ts(66 pass),bundler_string.test.ts(59 pass),transpiler/{property,runtime-transpiler,template-literal}.test.tsandtranspiler-cache.test.ts(20 pass).