Remove dead code from the class generator: the unreachable DOMJIT paths

[robobun]

Problem

• src/codegen/generate-classes.ts still has the DOMJIT emitter (C++ signatures, WithoutTypeChecks wrappers, result-type asserts, Rust thunks). None of it can run: define() in class-definitions.ts has set DOMJIT = undefined on each field since disable most DOMJIT #14005 (2024-09), and all 31 *.classes.ts files go through define().
• Nothing is left for it to bind: Remove ~39k lines of dead Rust across the workspace #35002 deleted each Rust *_without_type_checks fast path, and Remove dead code from webcore DOMJIT/EventPath/EventContext and misc C++ bindings #36756 and Remove dead code from webcore events/abort C++, ZigGeneratedCode DOMJIT, bun_alloc, libarchive, http #36903 removed the C++ leftovers.
• A DOMJIT: option in a .classes.ts file does nothing. Five exist.

Fix

• Delete the emitter, the option type, the strip in define(), the five ignored blocks, and the stale notes next to them: 6 files, 273 lines removed.
• The generated output is the same except for 94 empty #if BUN_DEBUG/#endif pairs in ZigGeneratedClasses.h and three DOMJIT-only #includes in ZigGeneratedClasses.cpp. generated_classes.rs is byte-identical.
• Verified: the generator run before and after, bun bd, tsc -p src, and the tests in the Notes.
• Self-reviewed: 13 concerns raised, 13 addressed (Notes).

Background

• DOMJIT is the JavaScriptCore fast path that lets the JIT call a host function with unboxed, type-checked arguments. The generator could emit a C++ signature and a Rust thunk for each method.
• The hand-written DOMJIT users (Buffer.alloc, performance.now, bun:ffi) do not use this generator. They stay.
• Earlier sweeps (Remove dead code from webcrypto, the node:http binding, the class codegen, build scripts, and misc crates #39249, Remove dead code from bun_url, bun_react_compiler, the class codegen, and bun-error #41169) called this removal a design call. This PR asks for that call alone.

Downsides

• To turn generated DOMJIT on again, a person must restore these paths from git history and write the Rust fast paths again.
• No runtime cost found. Checked: the generated .cpp, .h and .rs differ only as Fix says.

Notes

Removed

• generate-classes.ts: DOMJITName, argTypeName, DOMJITType, DOMJITFunctionDeclaration, DOMJITFunctionDefinition, domJITTypeCheckFields, RustDOMJITArgType. Also the DOMJIT branches in zigExportName, propRow, renderDecls, the expectedResultType asserts in the host-function wrapper, both Rust thunk loops, and the DOMJITAbstractHeap.h, FrameTracers.h, DFGAbstractHeap.h includes of the generated prologue. The destructures that named DOMJIT also lose the unused cache and value bindings.
• class-definitions.ts: the DOMJIT?: option type and the two .map() calls in define() that erased it.
• Ignored live blocks: Crypto.randomUUID, Crypto.timingSafeEqual (crypto.classes.ts), ServerWebSocket.publishText, publishBinary (server.classes.ts), TextDecoder.decode (encoding.classes.ts).
• Stale notes: the commented-out // DOMJIT: { blocks with their crash notes on sendText, sendBinary (2023) and getRandomValues (Disable DOMJIT for crypto.getRandomValues() #13470, 2024-08), and three orphan "DOMJIT fast path" comments in src/runtime/webcore/Crypto.rs whose functions Remove ~39k lines of dead Rust across the workspace #35002 deleted.

Self-review, and what changed because of it

• The first draft mixed this design call with 22 log scopes and seven fields. It now ships alone, with its history in the body.
• The leftover DOMJIT notes (Crypto.rs, the commented-out blocks) are folded in.
• Three deletions that open PRs carry were dropped (Remove dead code from the JSC bindings, headers.h, the console builtin, and bun_jsc #40232, Remove dead code from bun_core, the JSC bindings, the debugger, and 24 other crates #41385).
• Five items that open PRs use were taken out of the held branch (bun test: count code that runs in a Worker under --coverage #43283, Restore smol-gated retain-with-limit reset for the module loader transpile arena #31855, Remove libuv on Windows #42819, watch: reap child processes inherited across a --watch restart #39222, event_loop: replace JsPoster's hand-rolled vtable with Arc<dyn JsPost> #37518). Two builtins.d.ts lines were dropped too: src/codegen/replacements.ts defines $ImportKindLabelToId, so that declaration is live.

History

• Disable DOMJIT for crypto.getRandomValues() #13470 (2024-08) turned DOMJIT off for getRandomValues. disable most DOMJIT #14005 (2024-09) added the strip in define() as the repair for the try/catch not catching an error + Segmentation fault when executing TextDecoder.decode #14001 segfault. DOMJIT wrappers: route returns through OPERATION_RETURN #35224 found the cause (the wrappers returned { result } with a null exception slot) and tried to repair the generated wrappers. A stale-PR cleanup closed it with no maintainer comment. Remove ~39k lines of dead Rust across the workspace #35002 deleted the Rust fast paths, so the option cannot come back without new native code.

Kept on purpose

• The hand-written DomCall path for bun:ffi (src/jsc/host_fn.rs, src/runtime/ffi), the C++ DOMJIT signatures in JSBuffer.cpp, JSPerformance.cpp, NodeVM.cpp, JSSQLStatement.cpp, and test/js/bun/jsc/domjit.test.ts.

Tests (debug build)

• test/js/web/encoding/text-decoder.test.js 127 pass, test/js/web/web-globals.test.js 23 pass, test/js/bun/util/randomUUIDv5.test.ts 40 pass, test/js/bun/websocket/websocket-server.test.ts -t sendBinary 5 pass.
• websocket-server.test.ts -t "publish|send": 44 pass, 4 time out near 19 s under debug+ASAN. A debug binary built from main fails the same 4.
• test/js/bun/jsc/domjit.test.ts: 40 pass, 10 time out at the 100k-iteration sizes. A debug binary built from main gives the same 40/10.

The rest of this sweep

• Relink of the debug build with -Wl,--gc-sections, then the DWARF line table of the result: 2,290 of 31,118 Rust fns have no live line. After cargo check on six targets only three pub fns had no caller anywhere. The 96 trait impls with no caller are the ones Remove dead code: 49 trait impls nothing uses, across 12 crates #43664 kept on purpose.
• clang -fsyntax-only -Wunused-function -Wunused-template -Wunused-member-function -Wunused-macros over bun's 177 C/C++ translation units (the build passes -Wno-unused-function): ten hits. Open PRs delete them, or an #if uses them.
• oxlint no-unused-vars over src/js, src/codegen, scripts, packages. cargo's unused_dependencies lint over four targets. A scan for commented-out blocks (62 lines in the repo). Nothing new that is certain.
• Each deletion was compared with the diffs of the 36 open dead-code PRs. Left out because an open PR has it: Bun__napi_get_version (Remove dead code from the JSC bindings, headers.h, the console builtin, and bun_jsc #40232), two unused generator locals (Remove dead code from bun_core, the JSC bindings, the debugger, and 24 other crates #41385).

Verified and held for the next run (branch robobun/9a0817f5/dead-code-scopes-fields, 25 files, 81 lines removed)

• 20 declare_scope! scopes that nothing logs to: JSC, STR, Bundle and scan_counter (outer pair), Store, hot_reloader, CLI, LibUVBackend, ResolveInfoRequest, GetHostByAddrInfoRequest, CAresNameInfo, GetNameInfoRequest, CAresReverse, CAresLookup, quic_session, PathWatcherManager, S3Client, S3Stat, AWS, uws (uws_sys/socket.rs). rustc does not lint an item that another crate's macro expands.
• Fields: Runtime::Features.jsx_optimization_inline with the local can_be_inlined, DebugOptions.output_file, ArchiveIterator.filter, PackageManager.total_scripts, CommandLineArguments.lockfile, ArgumentsSlice::_vm. Also struct_Channeldata and two empty modules in napi_body.rs.
• It passed rust:check-all (12 targets), release and --cfg bun_debug --cfg bun_asan checks on linux, windows and darwin, and cargo check --tests before the trim below. The trimmed commit passes cargo check on linux.
• Taken out because an open PR uses the item: BundleOptions.code_coverage (bun test: count code that runs in a Worker under --coverage #43283 reads it), scope ModuleLoader (Restore smol-gated retain-with-limit reset for the module loader transpile arena #31855), scope PROCESS (Remove libuv on Windows #42819, watch: reap child processes inherited across a --watch restart #39222), impl Clone for JsPoster and its vtable slot (event_loop: replace JsPoster's hand-rolled vtable with Arc<dyn JsPost> #37518 rewrites the vtable).

Follow-up candidates, not verified dead

• Parser Options.preserve_unused_imports_ts is never true. tsconfig importsNotUsedAsValues is parsed into preserve_imports_not_used_as_values but never reaches the parser, in the released binary too. This looks like a missing feature.
• completions/bun-cli.json (4,513 lines) and misctools/generate-cli-completions.ts (728 lines): nothing in the repo reads the JSON, but feature PRs still edit it by hand.
• bench/snippets/runner-entrypoint.js (244 lines): no reference, first line says "this isn't done yet", last real change 2023-05.
• Ten impl_timer_owner! accessors have no caller because dispatch.rs recovers the owner with its own owner! macro. Which mechanism stays is a design call.
• mordant-baseline.toml still counts about 170 unused_pub findings (sys/lib.rs 56, libuv_sys/libuv.rs 41, errno/windows_errno.rs 31). bun run rust:mordant names them.

[robobun]

Status: open, waiting for CI and review.

How to check the change:

• Run bun src/codegen/generate-classes.ts $(bun scripts/glob-sources.ts zigGeneratedClasses) <out> <types> on main and on this branch, then diff -r the two output directories. The only differences are 94 empty #if BUN_DEBUG/#endif pairs in ZigGeneratedClasses.h and three #include lines in ZigGeneratedClasses.cpp.
• rg -n DOMJIT src/codegen finds nothing on this branch.

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📥 Commits

Reviewing files that changed from the base of the PR and between 6d504dd and 4561f47.

📒 Files selected for processing (6)

• src/codegen/class-definitions.ts
• src/codegen/generate-classes.ts
• src/runtime/crypto/crypto.classes.ts
• src/runtime/server/server.classes.ts
• src/runtime/webcore/Crypto.rs
• src/runtime/webcore/encoding.classes.ts

💤 Files with no reviewable changes (4)

• src/runtime/webcore/encoding.classes.ts
• src/runtime/server/server.classes.ts
• src/runtime/webcore/Crypto.rs
• src/runtime/crypto/crypto.classes.ts

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Walkthrough

The Field function-field type and runtime class definitions no longer use DOMJIT metadata. Class generation no longer emits DOMJIT-specific wrappers, checks, fields, fast-path thunks, or support includes. timingSafeEqual now declares a function length of 2.

Changes

DOMJIT removal

Layer / File(s)	Summary
Remove DOMJIT metadata src/codegen/class-definitions.ts, src/runtime/crypto/crypto.classes.ts, src/runtime/server/server.classes.ts, src/runtime/webcore/Crypto.rs, src/runtime/webcore/encoding.classes.ts	The Field function-field type and runtime class definitions no longer include DOMJIT metadata. define() still sorts klass and proto entries by key. DOMJIT fast-path comments are removed from Crypto.rs.
Remove DOMJIT-specific generated code src/codegen/generate-classes.ts	Generated property tables use ordinary native-function entries. Generation no longer emits DOMJIT exports, wrappers, type checks, class fields, fast-path thunks, or DOMJIT support headers.

Suggested reviewers: jarred-sumner

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 4561f

No actionable merge-blocking issue is established; the change is mergeable after normal checks.

🚥 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 main change: removal of unreachable DOMJIT paths from the class generator.
Description check	✅ Passed	The description explains the problem, fix, scope, retained behavior, risks, and verification results. It does not use the exact template headings, but it provides the required information in equivalen…

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[claude]

Code review found no issues

No high-confidence issues detected in this change.