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The linked source map comment was written with the raw output name and the raw publicPath. A LF, CR, U+2028 or U+2029 in an entry file name, in a naming template, or in publicPath ended the line comment, and the rest ran as code when the bundle was loaded. All three places that append the comment (in-memory build, build to disk, standalone HTML) now call one helper. The file path part is encoded as a URL path with the set esbuild uses. publicPath keeps printable ASCII, so URL syntax and existing escapes survive.
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Status Reproduced on 1.4.3 (b993710) with the script from the report: an entry named With this branch the comment is Self-reviewed: the review asked for an accurate scope statement (the body now lists every other place that writes these strings raw), an append form of the helper, and a lint for new |
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Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review. WalkthroughThe bundler now uses shared source-map URL comment generation. The helper percent-encodes unsafe bytes in public paths and relative filenames. Linked source-map output paths use the helper, with regression tests covering line terminators, URL characters, and output modes. ChangesSource-map URL encoding
Suggested reviewers: Priority: ⬆️ High Merge Risk: ⚪ Minimal · up to The source-map URL encoding change covers the reviewed output paths and prevents injected content from executing; no merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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In `@test/bundler/bun-build-api.test.ts`:
- Around line 1504-1509: Replace the parameter loop in the parameterized test
with a describe.each() matrix over the label, terminator, and encoded values,
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I reviewed this and found no bugs. Because it makes a deliberate design call — keeping all printable ASCII in publicPath rather than path-escaping it like esbuild does — and overlaps with #40834, a maintainer should confirm the two keep-sets are the encoding they want to ship.
What was reviewed:
- All three raw-concat sites route through the new helper; no fourth site was missed (grepped for
sourceMappingURL=insrc/bundler/). percent_encodeiterates per-byte with a predicate — not a byte search, so it does not hit thestrings/memchrlint; the under-sizedwith_capacityis only a hint andVecgrows on the rare escape path.is_url_path_bytematches Go'sencodePathreserved set minus:; U+2028/U+2029 encode byte-wise as%E2%80%A8/%E2%80%A9because none of their UTF-8 bytes are ASCII-graphic.- Tests cover both the disk and in-memory append paths, all four ECMAScript line terminators, the CLI/standalone-HTML path, and round-trip
decodeURIComponentback to the on-disk map; Windows skips are gated on the actual filesystem constraint (control chars only), so the U+2028/U+2029 cases still run there.
Extended reasoning...
Overview
The PR replaces three copy-pasted //# sourceMappingURL= builders (two in generateChunksInParallel.rs — the standalone/HTML-inline path and the general in-memory chunk path — and one in writeOutputFilesToDisk.rs) with a single with_source_mapping_url_comment helper in src/bundler/Chunk.rs. The helper percent-encodes both halves of the URL: the publicPath prefix keeps every ASCII graphic byte (0x21–0x7E), and the relative map path keeps Go's URL.EscapedPath set minus :. Six new tests in bun-build-api.test.ts and one in standalone.test.ts cover the four ECMAScript line terminators across both build modes, plus URL-syntax preservation and a CLI --compile --target=browser case.
Security risks
This is a hardening fix for a real injection: a LF/CR/U+2028/U+2029 in an entry filename or publicPath previously terminated the // comment and let the remainder execute when the bundle loaded. The new encoder closes that for this comment. I checked that both keep-sets exclude every byte of every ECMAScript line terminator (LF and CR fail is_ascii_graphic; the UTF-8 bytes of U+2028/U+2029 are all ≥ 0x80). The worst-case regression is over-encoding a byte a debugger expects raw, which is a source-map-lookup inconvenience, not a security regression. The PR description honestly enumerates the other raw-write sites (chunk-reference substitution into JS/CSS/HTML, the SourceMap header, //# sourceURL=) that this PR intentionally does not touch — those are tracked separately, so this is not silently claiming to close the whole class.
Level of scrutiny
Moderate. The Rust change is ~50 net new lines and three mechanical call-site replacements, all in the bundler's output-assembly layer. It follows the repo's rules closely: escaping lives in the shared output layer, bun_core::fmt::hex2_upper for hex, load-bearing one-line comments citing the reference (Go's URL.EscapedPath), tempDir/describe.concurrent/test.skipIf(isWindows) with a stated reason, exact toEqual assertions on the full comment, and both code paths exercised per case. The percent_encode loop is a per-byte predicate test rather than a substring/byte search, so the bun_core::strings lint does not apply. No CODEOWNERS entry covers src/bundler/.
Other factors
The one thing that warrants a human look is the encoding policy itself: this PR intentionally diverges from esbuild by leaving publicPath's printable ASCII intact (so [::1], #, ?, and pre-existing %20 survive), where esbuild path-escapes it and breaks those. The reasoning is sound and documented, but it is a user-visible behavior choice that also differs from the competing #40834, so a maintainer should sign off on the two keep-sets before merge. Beyond that, the bug-hunt ran to a dry streak with no findings and no ruled-out candidates, and the PR timeline shows no outstanding reviewer objections.
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Updated 9:17 PM PT - Sep 13th, 2026
✅ @robobun, your commit 40eff9e7905d9a42f57799ed9e4479916261c81b passed in 🧪 To try this PR locally: bunx bun-pr 42670That installs a local version of the PR into your bun-42670 --bun |
… for raw writers append_source_mapping_url_comment writes the encoded comment into a Vec, for writers that build their output in one. The lint fails when a file other than the encoder, the dev server (hex id) and the reader has a string literal that stops at `//# sourceMappingURL=`, which is what a writer that appends its own URL looks like.
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Problem
Bun.buildwithsourcemap: "linked"writes//# sourceMappingURL=with the raw output name and the rawpublicPath. A LF, CR, U+2028 or U+2029 in either ends the line comment, and the rest runs as code when the bundle loads://# sourceMappingURL=page\nglobalThis.INJECTED = 'ran';var y={js:{map:1}};y.js.map..json,.txt,.toml,.yaml,.md): its content cannot carry code, its name can.extend_from_slice:src/bundler/linker_context/generateChunksInParallel.rs(in-memory build, standalone HTML) andwriteOutputFilesToDisk.rs. For standalone HTML the code lands in the inline<script>.Fix
src/bundler/Chunk.rs. It percent-encodes both parts of the URL. A new source lint fails on a writer that does not.URL.EscapedPath), without:. A space is%20,#is%23,%is%25. Those were wrong before too.publicPathkeeps printable ASCII:?,#, an[::1]host and%20stay as written. This closes the comment only. Other places still write it raw (Notes).test/bundler/bun-build-api.test.ts, 1 instandalone.test.ts. All fail on 1.4.3 (Linux, Windows).Background
.mapfile. They resolve it as a URL relative to the script and percent-decode it.//comment ends at LF, CR, U+2028 or U+2029.<file>.map.publicPathraw.Notes
Repro from the report, before and after (debug build):
The same name on a
.json,.txt,.toml,.yamlor.mdentry gives the same result on 1.4.3. A.jsentry is the weaker case: who can add a.jsfile to the entry tree already controls code in the bundle.Standalone HTML (
bun build --compile --target=browser --sourcemap=linked "in\ndex.html" --outdir dist), before:On Windows a file name cannot contain LF or CR, but it can contain U+2028 and U+2029. The two tests for those run there and fail on the current canary.
What esbuild 0.28.2 writes for the same inputs (checked with its JS API):
esbuild path-escapes
publicPathtoo. That breaks an IPv6 host and encodes%20a second time, so this PR does not copy that part. esbuild also replaces:,*and control characters in output names with_before this step. Bun keeps the name, so:is encoded here:a:b.js.mapas a relative URL parses as schemea.Not in this PR. Each of these writes the same two strings somewhere else:
publicPathand the output path are written raw into JS string literals when a chunk or asset path is substituted at chunk assembly (IntermediateOutput::codeinsrc/bundler/Chunk.rs).publicPath: '/cdn/";globalThis.X=1;"'with onefileloader import still runs code there. bundler: JS-escape file-loader asset paths at chunk assembly #34188 and bundler: escape what is spliced into JS chunks (ASCII for bun), and fix the column count source map shifts use after non-ASCII text #38666 cover that place.url(): css: quote and escape the asset path spliced into url() #41557. Into an HTMLsrcorhref: bundler(html): percent-encode output paths written into src and href, and serve them under that name #41793.SourceMapresponse header thatBun.servesends for an HTML bundle in development (src/runtime/server/HTMLBundle.rs) is the raw output path.sourcesin the.mapfile stays raw. It is a JSON string, and Bun reads it raw.//# sourceURL=<path>raw after each module when the inspector is on (src/jsc/VirtualMachine.rs). A line break in the path breaks out the same way. Percent-encoding is wrong there, because stack traces print that directive. It is tracked separately.The lint (
source-mapping-url-writers.test.ts) lists the three files that may hold a string literal that stops at//# sourceMappingURL=: the encoder, the dev server (it appends a hex id) and the reader. #41939 adds a fourth writer insrc/bundler/transpiler.rsthat copiespublicPathand the path raw. It can callappend_source_mapping_url_comment.Suites run on a debug build:
test/bundler/bun-build-api.test.ts,standalone.test.ts,cli.test.ts,bundler_html.test.ts,bundler_edgecase.test.ts,bun-build-compile-sourcemap.test.ts,compile-sourcemap-internal.test.ts,bundler_compile.test.ts -t sourcemap,esbuild/default.test.ts,esbuild/splitting.test.ts,test/js/bun/http/bun-serve-html.test.ts,test/regression/issue/cyclic-imports-async-bundler.test.js,test/internal/source-lints/byte-search.test.ts. Two bytecode tests inbun-build-api.test.tshit the 5 s default timeout on a debug build. They do not use source maps.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/bundler/standalone.test.ts, test/bundler/bun-build-api.test.ts