bun-types: accept every TextDecoder encoding label the runtime supports by robobun · Pull Request #40119 · oven-sh/bun

robobun · 2026-08-22T18:31:09Z

Fixes #40117

Problem

new TextDecoder("windows-1251") works at runtime, but @types/bun rejects it: error TS2345: Argument of type '"windows-1251"' is not assignable to parameter of type 'Encoding | undefined'.
Bun.Encoding (packages/bun-types/bun.d.ts:31) lists only "utf-8" | "windows-1252" | "utf-16". The runtime accepts the full WHATWG label table through src/runtime/webcore/EncodingLabel.rs.

Fix

Widen Bun.Encoding to the 222 labels the runtime accepts: the Encoding Standard table minus the six labels of the replacement encoding, which the TextDecoder constructor rejects with a RangeError.
The union is generated from the runtime label table in EncodingLabel.rs and grouped by canonical name, so it matches the runtime exactly.
Enable the fixture test/integration/bun-types/fixture/text-encode-decoder.ts (it was fully commented out). It asserts the union equals the label table in both directions and constructs a TextDecoder for every label. A new tsc-spawn test in bun-types.test.ts covers the same labels and runs on debug builds.
Verified: bun test test/integration/bun-types/bun-types.test.ts passes (16/16, includes the lib.dom and tsgo runs). With the old bun.d.ts, the new test fails with the TS2345 above.

Background

Bun.Encoding is the constructor parameter type of the global TextDecoder and TextEncoder when lib.dom is absent. With lib.dom, the declaration defers to the DOM one, which takes a plain string.
The runtime resolves labels per https://encoding.spec.whatwg.org/#names-and-labels, ASCII case-insensitive. Aliases such as latin1, utf8, and shift_jis are valid at runtime and now type-check.
TextEncoder keeps its optional parameter. The runtime ignores it and always encodes UTF-8, so the widened type stays accurate there, and a narrower signature would break existing callers.

Notes

Runtime checks on 1.4.0-canary: new TextDecoder("hz-gb-2312") throws RangeError: Unsupported encoding label "hz-gb-2312" (replacement family), new TextDecoder("bogus") throws RangeError, and new TextEncoder("windows-1251").encoding is "utf-8". That is why the union excludes the replacement labels and why the TextEncoder signature is unchanged.
The fixture negative cases use "..." satisfies Bun.Encoding instead of @ts-expect-error on the constructor, so they also hold in the lib.dom run, where the DOM TextDecoder accepts any string.
The stale JSDoc on the global TextDecoder ("only support UTF-8 decoding") is updated.
History: Support windows-1251 encoder in TextDecoder #6084 tracked runtime support (closed completed). Type error in TextDecoder type signature #18747 asked for the wider type before the runtime supported these encodings (closed not planned).

[review] gate passed · iteration 0 · 4 files touched

fails on main (without fix)

ASAN without fix: 1 failed, 12 skipped
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/integration/bun-types/bun-types.test.ts
bun test v1.4.1 (4448a2e21)

test/integration/bun-types/bun-types.test.ts:
(pass) @types/bun integration test > building and packing bun-types leaves packages/bun-types untouched [4.17ms]
(pass) @types/bun integration test > packed bun-types includes CLAUDE.md [10.70ms]
(skip) @types/bun integration test > basic type checks > checks without lib.dom.d.ts
(skip) @types/bun integration test > tsgo (TypeScript 7 native preview) > checks without lib.dom.d.ts
(pass) @types/bun integration test > Bun.mmap > MMapOptions accepts offset and size [1144.22ms]
430 |       });
431 | 
432 |       const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
433 | 
434 |       expect(stderr.trim()).toBe("");
435 |       expect(stdout.trim()).toBe("");
                                  ^
error: expect(received).toBe(expected)

- ""
+ "text-decoder-encodings.ts(1,17): error TS2345: Argument of type '"windows-1251"' is not assignable to parameter of type 'Encoding
... (truncated)

release without fix: 10 FAILED
bun test v1.4.0-canary.1 (4448a2e21)

test/integration/bun-types/bun-types.test.ts:
(pass) @types/bun integration test > building and packing bun-types leaves packages/bun-types untouched [0.13ms]
(pass) @types/bun integration test > packed bun-types includes CLAUDE.md [0.29ms]
131 |     expect(emptyInterfaces).toEqual(config.emptyInterfaces);
132 | 
133 |     if (typeof config.diagnostics === "function") {
134 |       config.diagnostics(diagnostics);
135 |     } else {
136 |       expect(diagnostics).toEqual(config.diagnostics);
                                ^
error: expect(received).toEqual(expected)

- []
+ [
+   {
+     "code": 1360,
+     "line": "text-encode-decoder.ts:270:8",
+     "message": 
+ "Type 'readonly ["unicode-1-1-utf-8", "unicode11utf8", "unicode20utf8", "utf-8", "utf8", "x-unicode20utf8", "866", "cp866", "csibm866", "ibm866", "csisolatin2", "iso-8859-2", "iso-ir-101", ... 208 more ..., "x-user-defined"]' does not satisfy the expected type 'readonly Encoding[]'.
+ Type '"gb2312" | "ascii" | "utf8" | "utf-8" | "utf-16le" | "ucs-2" | "latin1" | "windows-1252" | "utf-16" | "unicode" | "unicode-1-1-utf-8" | "unicode11utf8" | "unicode20utf8" | "x-uni
... (truncated)

passes on PR (with fix)

ASAN with fix: 12 skipped
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/integration/bun-types/bun-types.test.ts
bun test v1.4.1 (4448a2e21)

test/integration/bun-types/bun-types.test.ts:
(pass) @types/bun integration test > building and packing bun-types leaves packages/bun-types untouched [3.00ms]
(pass) @types/bun integration test > packed bun-types includes CLAUDE.md [6.99ms]
(skip) @types/bun integration test > basic type checks > checks without lib.dom.d.ts
(skip) @types/bun integration test > tsgo (TypeScript 7 native preview) > checks without lib.dom.d.ts
(pass) @types/bun integration test > Bun.mmap > MMapOptions accepts offset and size [1485.64ms]
(pass) @types/bun integration test > TextDecoder > accepts the encoding labels the runtime supports [1630.35ms]
(pass) @types/bun integration test > TextDecoder > the fixture label table matches the runtime [97.87ms]
(skip) @types/bun integration test > Test Globals > checks without lib.dom.d.ts and test-globals references
(skip) @types/bun integration test > Test Globals > test-globals FAILS when the test-globals.d.ts is not referenced
(skip) @type
... (truncated)

release with fix: all passed
$ bun scripts/build.ts --profile=release
[configured] bun-profile → bun (stripped) in 1626ms (unchanged)
ninja: Entering directory `/workspace/bun/build/release'
[0/5] cargo bun_runtime → libbun_runtime.a (--target x86_64-unknown-linux-gnu)

  nightly-2026-07-20-x86_64-unknown-linux-gnu unchanged - rustc 1.99.0-nightly (9f36de775 2026-07-19)

�[1m�[92m   Compiling�[0m bun_core v0.0.0 (/workspace/bun/src/bun_core)
�[1m�[92m   Compiling�[0m bun_errno v0.0.0 (/workspace/bun/src/errno)
�[1m�[92m   Compiling�[0m bun_ptr v0.0.0 (/workspace/bun/src/ptr)
�[1m�[92m   Compiling�[0m bun_boringssl_sys v0.0.0 (/workspace/bun/src/boringssl_sys)
�[1m�[92m   Compiling�[0m bun_safety v0.0.0 (/workspace/bun/src/safety)
�[1m�[92m   Compiling�[0m bun_base64 v0.0.0 (/workspace/bun/src/base64)
�[1m�[92m   Compiling�[0m bun_cares_sys v0.0.0 (/workspace/bun/src/cares_sys)
�[1m�[92m   Compiling�[0m bun_zlib_sys v0.0.0 (/workspace/bun/src/zlib_sys)
�[1m�[92m   Compiling�[0m bun_collections v0.0.0 (/workspace/bun/src/collections)
�[1m�[92m   Compiling�[0m bun_zstd v0.0.0 (/workspace/bun/src/zstd)
�[1m�[92m   Compiling�[0m bun_paths v0.0.0 (/workspace/bun/src/paths)
�[1m�[92m   Compiling�[
... (truncated)

diff hotspot

packages/bun-types/bun.d.ts                        | 272 ++++++++++-
 packages/bun-types/globals.d.ts                    |   5 +-
 test/integration/bun-types/bun-types.test.ts       |  74 +++
 .../bun-types/fixture/text-encode-decoder.ts       | 501 ++++++++++++---------
 4 files changed, 636 insertions(+), 216 deletions(-)

gate history · 1 passed · 0 rejected · iteration 0

evidence per changed file

file                                                      reads  edits  tests
packages/bun-types/bun.d.ts                                   0      0      0
packages/bun-types/globals.d.ts                               1      1      0
test/integration/bun-types/bun-types.test.ts                  2      4      0
…st/integration/bun-types/fixture/text-encode-decoder.ts      1      0      0

root cause · written by the author bot

The Encoding type in bun-types was a stale three-member union that predated runtime support for the full WHATWG encoding label set, so TypeScript rejected constructor arguments like "windows-1251" that Bun's TextDecoder accepts at runtime. The fix expands the declaration to cover every label in the runtime's encoding table while deliberately excluding the six replacement-encoding labels, which the constructor rejects with a RangeError. A literal fixture in the bun-types integration tests keeps the declaration honest by exercising each label against the running TextDecoder and asserting that…

coderabbitai · 2026-08-22T18:34:54Z

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Walkthrough

Changes

TextDecoder encoding support

Layer / File(s)	Summary
Expand the encoding contract `packages/bun-types/bun.d.ts`, `packages/bun-types/globals.d.ts`	`Bun.Encoding` now includes the supported WHATWG encoding labels. `TextDecoder` documentation reflects this support.
Validate encoding labels `test/integration/bun-types/fixture/text-encode-decoder.ts`, `test/integration/bun-types/bun-types.test.ts`	The fixture and integration tests verify supported and rejected labels, decoder options, decoder construction, runtime errors, and `TextEncoder` usage.

Suggested reviewers: alii

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR addresses issue `#40117` by aligning Bun.Encoding with all runtime-supported TextDecoder labels, including aliases such as windows-1251.
Out of Scope Changes check	✅ Passed	The type changes, documentation update, and compatibility tests are directly related to the linked issue and stated PR objectives.
Title check	✅ Passed	The title clearly and concisely summarizes the main change to support all runtime-supported TextDecoder encoding labels in bun-types.
Description check	✅ Passed	The description explains the problem, fix, testing, runtime behavior, and linked issue, although it does not use the exact template headings.

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Inline comments:
In `@packages/bun-types/bun.d.ts`:
- Around line 40-301: Update the encoding-label validation around the Encoding
type to compare against the runtime-backed Bun.Encoding labels, filtering out
the six Replacement labels before comparison. Remove the duplicated hard-coded
label fixture while preserving validation that the remaining union entries match
the accepted runtime labels.

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Inline comments:
In `@test/integration/bun-types/bun-types.test.ts`:
- Around line 450-451: Add a uniqueness assertion for the labels parsed in the
fixture test alongside the existing length assertion, using the labels
collection and preserving the requirement that all 222 expected labels are
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robobun · 2026-08-22T18:40:17Z

^{Updated 12:01 PM PT - Aug 22nd, 2026}

✅ @robobun, your commit 9f6e8f86fbab872b00fd3f8c12ec2a25ec3243e1 passed in Build #103667! 🎉

🧪 To try this PR locally:

bunx bun-pr 40119

That installs a local version of the PR into your bun-40119 executable, so you can run:

bun-40119 --bun

claude

LGTM — widens Bun.Encoding to the full WHATWG label set the runtime already accepts.

What was reviewed

Verified the 222-label union in bun.d.ts and the fixture array are identical, unique, and match the Encoding Standard table minus the six replacement labels.
Confirmed Bun.Encoding is only consumed by the TextEncoder/TextDecoder constructor signatures in globals.d.ts, so widening is purely additive.
Checked the fixture's bidirectional satisfies checks and @ts-expect-error negatives hold with and without lib.dom (they target Bun.Encoding, not the constructor).

Extended reasoning...

Overview

This PR widens the Bun.Encoding string-literal union in packages/bun-types/bun.d.ts from 3 labels to the 222 labels the runtime's TextDecoder actually accepts (the WHATWG Encoding Standard table minus the six replacement labels, which the constructor rejects). It updates the stale JSDoc on the global TextDecoder, enables the previously commented-out text-encode-decoder.ts fixture with bidirectional type-level satisfies checks, and adds two tests to bun-types.test.ts: a spawned-tsc check (mirroring the existing Bun.mmap block) and a runtime check that constructs a TextDecoder for every fixture label and asserts the replacement labels throw RangeError.

Security risks

None. This is a .d.ts-only change plus test coverage; no runtime code, native code, or build machinery is touched.

Level of scrutiny

Low. Type-declaration widening is strictly additive — every value the old union accepted is still accepted. The only downstream consumers of Bun.Encoding are the TextEncoder/TextDecoder constructor signatures (verified via grep), and both are wrapped in UseLibDomIfAvailable so lib.dom users are unaffected. I independently verified the union has exactly 222 unique labels, the fixture array is byte-identical to the union, and the fixture's labels satisfies readonly Bun.Encoding[] + anyEncoding satisfies (typeof labels)[number] pair enforces the two sets stay equal at the type level.

Other factors

The new tests follow the existing Bun.mmap describe block's pattern exactly (spawned tsc against a temp tsconfig with typeRoots pointing at the packed @types/bun). The runtime-vs-fixture test parses the fixture source, asserts 222 unique labels, and ties them to the running binary — addressing the CodeRabbit feedback about drift from EncodingLabel.rs. Both CodeRabbit threads are resolved, and the uniqueness assertion was added in 9f6e8f8. The PR description confirms the full test file (16/16, including the lib.dom and tsgo runs) passes.

bun-types: widen Encoding to every label the TextDecoder runtime accepts

0f7c804

robobun requested a review from alii as a code owner August 22, 2026 18:31

robobun mentioned this pull request Aug 22, 2026

Bun 1.4 TextDecoder accepts windows-1251 at runtime but bun-types rejects it #40117

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github-actions Bot added the claude label Aug 22, 2026

coderabbitai Bot reviewed Aug 22, 2026

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Comment thread packages/bun-types/bun.d.ts

robobun and others added 2 commits August 22, 2026 18:36

test: check the fixture encoding labels against the running binary

6c40b4f

[autofix.ci] apply automated fixes

ddc0b3b

coderabbitai Bot reviewed Aug 22, 2026

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Comment thread test/integration/bun-types/bun-types.test.ts

test: assert the fixture encoding labels are unique

9f6e8f8

claude Bot reviewed Aug 22, 2026

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Jarred-Sumner merged commit 6d9d04d into main Aug 23, 2026
8 checks passed

Jarred-Sumner deleted the farm/1b06837a/textdecoder-encoding-types branch August 23, 2026 05:11

robobun mentioned this pull request Aug 30, 2026

bun-types: keep generic process.removeListener and off signatures visible with @types/node 24 #40004

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This was referenced Sep 7, 2026

types: add Bun's FreeBSD platform values to navigator.platform #36278

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types: accept the Bun.color output formats the runtime supports #42470

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bun-types: accept every TextDecoder encoding label the runtime supports - #40119

bun-types: accept every TextDecoder encoding label the runtime supports#40119
Jarred-Sumner merged 4 commits into
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farm/1b06837a/textdecoder-encoding-types

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