[robobun]

Problem

• Code that nothing reaches remains in bun_css, bun_react_compiler, and a few smaller crates. dead_code = "deny" cannot see it: the items are pub, or trait impls, or fields that are written but never read, or branches behind an option that no caller ever sets.
• The largest pieces are two lightningcss features that Bun never enables (PrinterOptions.analyze_dependencies, and the CSS-modules export and reference tables) and the React Compiler logger event types that no code constructs.

Fix

• Delete the unreachable items and the plumbing that only fed them (46 files, -1471 +71 lines). Each symbol has zero references outside its own definition (rg -w over src/, packages/, scripts/, test/, build/debug/codegen/), and the workspace compiles with the items gone. The full list is in the Notes below.
• bun_css (-820): analyze_dependencies and the Dependency types, the CssModule export and reference tables, Config.dashed_idents and the from clause of DashedIdentReference, Segment::Name. bun_react_compiler (-385): the logger event types, the events, ordered_log and renames outputs, count_memo_blocks, never-constructed enum variants. Smaller crates (-266): RefCounted::debug_name, unused HasLength impls, tcc enum variants, bun_jsc error helpers, WeakRefType::PostgreSQLQueryClient, five RedisError variants, stale builtins.d.ts declarations.
• Add test/internal/source-lints/module-lint-escapes.test.ts: it pins the module-level #![allow(dead_code)] and #![allow(unreachable_pub)] escapes per file, like the item-level dead-code-escapes.test.ts. This change drops the escape in react_compiler/compile_result.rs, so the lint fails on main and passes here.
• Verified: bun bd, cargo check --workspace, bun run rust:check-all (12 targets), bun bd test on test/bundler/css, test/js/bun/css, test/bundler/transpiler/react-compiler-fixtures.test.ts, test/js/valkey, test/js/sql/local-sql.test.ts, test/js/sql/postgres-binary-numeric.test.ts, test/js/bun/ffi, test/js/bun/test/mock-fn.test.js, test/js/web/fetch/fetch.test.ts (same failures as a release build in this container), and test/internal/source-lints.

Background

• bun_css is a port of lightningcss. Bun renames CSS-module classes through the bundler symbol table, so the lightningcss export table was filled in and then dropped. analyze_dependencies replaces url() and @import with placeholders for a later rewrite pass. Bun resolves imports through ImportRecords instead, so the option was never set.
• The React Compiler port keeps upstream's logger event shapes. Bun never wires a logger, so the event types had constructors but no construction site.
• WeakRefType is the tag Bun passes to JSC weak handles so C++ knows which Rust finalizer to call. The PostgreSQLQueryClient arm declared a finalizer that was never defined.

Notes

Removed, per crate:

• bun_css: the exports_by_source_index and references maps of CssModule (written, never read) with get_reference, reference_dashed, add_dashed, add_local, CssModuleExports, CssModuleReferences, CssModuleExport, CssModuleReference; Config.dashed_idents (always false); DashedIdentReference.from and parse_with_options (always None); Pattern::write_to_string, Pattern::write_to_string_with_prefix, Segment::Name; the analyze_dependencies printer option with Dependency, ImportDependency, UrlDependency, DependencyOptions, Printer.{dependencies,remove_imports}, Printer::get_import_records, Printer::replace_dots, Url::is_absolute, PrinterErrorKind::ambiguous_url_in_custom_property; the is_declaration parameter of Printer::write_dashed_ident; the raw-pointer references setup in StyleSheet::to_css_with_writer_impl; three no-op #[cfg_attr(any(), derive(...))] attributes.
• bun_react_compiler: LoggerEvent, OrderedLogItem, DebugLogEntry, CompilerErrorDetailInfo, LoggerSuggestionInfo, LoggerSuggestionOp, CompilerErrorItemInfo, LoggerSourceLocation, LoggerPosition, BindingRenameInfo; the events, ordered_log and renames fields of CompileOutput with their producers (convert_renames, BindingRename, Environment.renames, ProgramContext.renames); count_memo_blocks with CountMemoBlockVisitor and the Debug impl for CodegenFunction that was its only reader; the four logged_severity methods; Display for ReactiveTerminalTargetKind; Error for CompilerError; ErrorCategory::{Suppression, FBT}, CompilerSuggestionOperation::{InsertBefore, InsertAfter, Remove}, JsxImportKind::CreateElement, ValueReason::StoreLocal; ExactSizeIterator, PartialEq, Eq and From<[K; N]> impls in collections.rs; the module-level #![allow(unreachable_pub)] in compile_result.rs.
• bun_ptr, bun_core_macros: RefCounted::debug_name, ThreadSafeRefCounted::debug_name, type_base_name, and the debug_name key of #[ref_count(...)] (four attribute sites updated).
• bun_core: HasLength impls for [u8], &str, &String.
• bun_tcc_sys: Error::{SyntaxError, ExecError, OutputError}, OutputFormat::{Exe, Dll, Obj, Preprocess} and the matching TCC_OUTPUT_* constants.
• bun_jsc: to_type_error_instance and to_range_error_instance on EncodedSliceJsc, to_syntax_error_instance and to_range_error_instance on StringJsc (the src/CLAUDE.md line that lists them is updated), WeakRefType::PostgreSQLQueryClient in Weak.rs and Weak.cpp.
• bun_valkey, bun_runtime: RedisError::{InvalidArgument, InvalidArray, InvalidBigNumber, InvalidErrorString, InvalidSimpleString} and the ERR_REDIS_INVALID_{ARGUMENT, ARRAY, ERROR_STRING, SIMPLE_STRING} rows in ErrorCode.ts.
• bun_sql_jsc: IntoOptionalData for &mut Data.
• codegen and JS: the notImplementedIssue rule in src/codegen/replacements.ts (only the Fn form is used), 54 stale declare lines in src/js/builtins.d.ts.

Items the sweep saw and left alone, with the reason:

• JSCrossRealmTransformState, CrossRealmTransform.cpp and the CrossRealm stream enum arms (about 176 lines): unreachable, but the header states they are kept on purpose for transferable streams, and DOMIsoSubspaces.h is included by every binding.
• macro(mockedFunction) and macro(writer) in BunBuiltinNames.h (2 lines): unused, but the header is included by every C++ file.
• The h2 Connection outbound encoder in src/runtime/api/bun/h2/ (about 250 lines, test-only): part of a planned engine rewrite that h2/mod.rs documents.
• React Compiler options that are parsed from pragmas but never read (enableEmitHookGuards, validateBlocklistedImports, customHooks, moduleTypeProvider, and the write-only EnvironmentConfig fields, about 280 lines): un-wired upstream features rather than dead code.
• MinifyOptions.unused_symbols, ParserOptions.error_recovery, PrinterOptions.pseudo_classes, PrinterOptions.project_root, ParserFlags::{CUSTOM_MEDIA, NESTING}, Targets.include in bun_css (about 125 lines): always default today, but they are real lightningcss features and the files are touched by open PRs Remove dead code from bun_core, bun_jsc, bun_css, react_compiler, and two C++ bindings #40367 and Remove dead code from the js lexer, bun_runtime, bun_alloc, and 20 other crates #40610.
• prefixes::Feature and compat::Feature variants nothing references (about 1300 lines): generated by src/css/build-prefixes.js, so the generator would need a filter first.
• src/js_parser/benches/string_map_vs_hashmap.rs (about 800 lines): a criterion bench, not runtime code.
• The .idl files under src/jsc/bindings/webcore and webcrypto: not compiled, but maintained as the reference for the hand-written bindings.
• bindings.cpp [[ZIG_EXPORT]] wrappers with no Rust caller (JSC__JSValue__isInt32, isNumber, isObject, isUndefined, isUndefinedOrNull, isNull, isCell, isInt32AsAnyInt, jsTDZValue, JSC__JSMap__has, Bun__CallFrame__isFromBunMain, about 45 lines): Remove dead code from the JSC bindings, headers.h, the console builtin, and bun_jsc #40232 edits the same file.
• ExportRenamer, Futex.rs wasm_impl, JsClassDerive, the commented-out fileURLToPath in node/url.ts, and the unused Cargo dependencies the scan found: already removed by Remove dead code from the inspector protocol package, bun_jsc, bun_install, and the Windows named pipe modules #40557, Remove dead code from bun-uws, bun-usockets, the require.extensions FFI, and unused Cargo dependencies #40294, Remove dead code from the JSC bindings, the codegen scripts, the CI scripts, bun_core, and bun_jsc #40492, or Remove dead code from the JSC bindings, headers.h, the console builtin, and bun_jsc #40232.

Candidates the compiler proved live, so they stay: Display for HookKind (used by name_anonymous_functions.rs), PendingCompile.binding (read in visit/mod.rs), Default for EditorContext (mem::take in BunObject.rs), CowSliceZ::dupe_maybe_z (used by into_owned).

Areas scanned and found clean: src/js/**, src/sql, src/valkey, src/runtime/webcore, src/runtime/node, src/runtime/{crypto,server,test_runner,bake,api,timer,ffi,napi,socket,shell}, src/http*, src/js_printer, src/runtime/cli, src/install, src/js_parser, src/bundler, src/jsc/*.rs, src/bun_core, 60 small crates, and the C++ bindings outside the files that open dead-code PRs touch.

---

[review] gate passed · iteration 1 · 49 files touched

fails on main (without fix)

ASAN without fix: 1 FAILED
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/internal/source-lints/module-lint-escapes.test.ts
bun test v1.4.1 (731aa92da)

test/internal/source-lints/module-lint-escapes.test.ts:
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/install/windows-shim/main.rs (1) [1.93ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/jsc/cpp.rs (1) [0.04ms]
86 |       if (count > limit) {
87 |         throw new Error(
88 |           `${source} has ${count} module-level dead_code/unreachable_pub escapes, up from ${limit}.\n` +
89 |             `A module-level escape hides every dead item in the file from the compiler. Delete the dead items or use pub(crate) instead.\n` +
90 |             `If the escape is justified, update the inventory with \`bun ./test/internal/source-lints/module-lint-escapes.test.ts --write\`.`,
91 |         );
             ^
error: src/react_compiler/compile_result.rs has 1 module-level dead_code/unreachable_pub escapes, up from 0.
A module-level escape hides every dead item in the file from the compi
... (truncated)

release without fix: 1 FAILED
bun test v1.4.1-canary.1 (a023e2016)

test/internal/source-lints/module-lint-escapes.test.ts:
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/install/windows-shim/main.rs (1) [0.04ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/jsc/cpp.rs (1)
86 |       if (count > limit) {
87 |         throw new Error(
88 |           `${source} has ${count} module-level dead_code/unreachable_pub escapes, up from ${limit}.\n` +
89 |             `A module-level escape hides every dead item in the file from the compiler. Delete the dead items or use pub(crate) instead.\n` +
90 |             `If the escape is justified, update the inventory with \`bun ./test/internal/source-lints/module-lint-escapes.test.ts --write\`.`,
91 |         );
             ^
error: src/react_compiler/compile_result.rs has 1 module-level dead_code/unreachable_pub escapes, up from 0.
A module-level escape hides every dead item in the file from the compiler. Delete the dead items or use pub(crate) instead.
If the escape is justified, update the inventory with `bun ./test/internal/source-lints/module-lint-escapes.test.ts --write`.
      at
... (truncated)

passes on PR (with fix)

ASAN with fix: all passed
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/internal/source-lints/module-lint-escapes.test.ts
bun test v1.4.1 (731aa92da)

test/internal/source-lints/module-lint-escapes.test.ts:
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/install/windows-shim/main.rs (1) [2.08ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/jsc/cpp.rs (1) [0.06ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/react_compiler/diagnostics/mod.rs (1) [0.05ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/react_compiler/hir/mod.rs (1) [0.04ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/react_compiler/inference/mod.rs (1) [0.05ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/react_compiler/optimization/mod.rs (1) [0.03ms]
(pass) module-level #![allow(dead_code)] / #![allow(unreachable_pub)] escapes > src/react_compiler/reactive_scopes/mod.rs (1) [0.03ms]
(pass) module-level #![allo
... (truncated)

release with fix: all passed
$ bun scripts/build.ts --profile=release
[configured] bun-profile → bun (stripped) in 779ms (unchanged)
ninja: Entering directory `/workspace/bun/build/release'
[1/82] gen ErrorCode+*.h
[2/27] gen generated_host_exports.rs
generated_host_exports.rs: 122 exports (host=5, lazy=10, generic=107, rust=0); 243 extern-C blocks audited
[3/27] gen cpp.rs (cppbind)
[4/27] gen JS modules (bundle-modules)
Preprocess modules (8116ms)
Bundle modules (45ms)
Postprocesss modules (34ms)
Bundle Functions (412ms)
Generate Code (29ms)

[8.64s] Bundled "src/js" for production
  2595 kb
  197 internal modules
  13 native modules
  50 internal functions across 16 files
[4/17] cargo bun_runtime → libbun_runtime.a
�[1m�[92m   Compiling�[0m bun_core v0.0.0 (/workspace/bun/src/bun_core)
�[1m�[92m   Compiling�[0m bun_core_macros v0.0.0 (/workspace/bun/src/bun_core_macros)
�[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
... (truncated)

diff hotspot

hawk.toml                                          |   8 -
 src/CLAUDE.md                                      |   2 +-
 src/bun_core/comptime_string_map.rs                |  21 --
 src/bun_core_macros/lib.rs                         |  23 +-
 src/codegen/replacements.ts                        |   4 -
 src/css/css_modules.rs                             | 287 +--------------------
 src/css/css_parser.rs                              |  41 +--
 src/css/dependencies.rs                            |  71 +----
 src/css/error.rs                                   |  10 -
 src/css/lib.rs                                     |   2 -
 src/css/printer.rs                                 | 160 ++----------
 src/css/properties/animation.rs                    |  19 --
 src/css/properties/background.rs                   |   2 -
 src/css/properties/css_modules.rs                  |  21 --
 src/css/properties/custom.rs                       |  69 +----
 src/css/properties/masking.rs                      |   6 -
 src/css/rules/import.rs                            |  24 +-
 src/css/rules/mod.rs                               |  24 --
 src/css/values/ident.rs                            |  82 +-----
 src/css/values/image.rs                            |  35 +--
 src/css/values/url.rs                              |  73 ------
 src/js/builtins.d.ts                               |  54 ----
 src/js_parser/react_compiler_host.rs               |   1 -
 src/jsc/EncodedSlice.rs                            |   8 -
 src/jsc/Weak.rs                                    |   1 -
 src/jsc/bindings/ErrorCode.ts                      |   4 -
 src/jsc/bindings/Weak.cpp                          |  10 +-
 src/jsc/bun_string_jsc.rs                          |   8 -
 src/ptr/ref_count.rs                               |  32 ---
 src/react_compiler/codegen.rs                      |  82 ------
 src/react_compiler/collections.rs                  |  22 --
 src/react_compiler/compile_result.rs               |
... (truncated)

gate history · 3 passed · 0 rejected · iteration 1

evidence per changed file

file                                 reads  edits  tests
hawk.toml                                1      2      0
src/CLAUDE.md                            0      0      0
src/bun_core/comptime_string_map.rs      0      0      0
src/bun_core_macros/lib.rs               0      0      0
src/codegen/replacements.ts              0      0      0
src/css/css_modules.rs                   0      0      0
src/css/css_parser.rs                    0      0      0
src/css/dependencies.rs                  0      0      0
src/css/error.rs                         0      0      0
src/css/lib.rs                           0      0      0
src/css/printer.rs                       0      0      0
src/css/properties/animation.rs          0      0      0
src/css/properties/background.rs         0      0      0
src/css/properties/css_modules.rs        0      0      0
src/css/properties/custom.rs             0      0      0
src/css/properties/masking.rs            0      0      0
(+ 33 more files)

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📥 Commits

Reviewing files that changed from the base of the PR and between a46c250 and 6d7ad04.

📒 Files selected for processing (49)

• hawk.toml
• src/CLAUDE.md
• src/bun_core/comptime_string_map.rs
• src/bun_core_macros/lib.rs
• src/codegen/replacements.ts
• src/css/css_modules.rs
• src/css/css_parser.rs
• src/css/dependencies.rs
• src/css/error.rs
• src/css/lib.rs
• src/css/printer.rs
• src/css/properties/animation.rs
• src/css/properties/background.rs
• src/css/properties/css_modules.rs
• src/css/properties/custom.rs
• src/css/properties/masking.rs
• src/css/rules/import.rs
• src/css/rules/mod.rs
• src/css/values/ident.rs
• src/css/values/image.rs
• src/css/values/url.rs
• src/js/builtins.d.ts
• src/js_parser/react_compiler_host.rs
• src/jsc/EncodedSlice.rs
• src/jsc/Weak.rs
• src/jsc/bindings/ErrorCode.ts
• src/jsc/bindings/Weak.cpp
• src/jsc/bun_string_jsc.rs
• src/ptr/ref_count.rs
• src/react_compiler/codegen.rs
• src/react_compiler/collections.rs
• src/react_compiler/compile_result.rs
• src/react_compiler/diagnostics/mod.rs
• src/react_compiler/hir/environment.rs
• src/react_compiler/hir/reactive.rs
• src/react_compiler/hir/type_config.rs
• src/react_compiler/imports.rs
• src/react_compiler/lowering/hir_builder.rs
• src/react_compiler/pipeline.rs
• src/react_compiler/program.rs
• src/runtime/api/bun/subprocess/SubprocessPipeReader.rs
• src/runtime/api/js_bundle_completion_task.rs
• src/runtime/server/HTMLBundle.rs
• src/runtime/valkey_jsc/protocol_jsc.rs
• src/sql_jsc/shared/SQLDataCell.rs
• src/tcc_sys/tcc.rs
• src/valkey/valkey_protocol.rs
• test/internal/source-lints/module-lint-escapes.json
• test/internal/source-lints/module-lint-escapes.test.ts

---

_{Comment @coderabbitai help to get the list of available commands.}

[robobun]

Status: ready for review. The diff is green; CI is red only on lanes this PR does not touch.

• Every removed symbol was checked with rg -w over src/, packages/, scripts/, test/, and the regenerated build/debug/codegen/, then confirmed by a green bun bd and bun run rust:check-all (12 targets).
• test/internal/source-lints/module-lint-escapes.test.ts fails on main (src/react_compiler/compile_result.rs carried a module-level #![allow(unreachable_pub)]) and passes on this branch.
• No deletion here duplicates an open dead-code PR. Shared files with Remove dead code from bun_core, bun_jsc, bun_css, react_compiler, and two C++ bindings #40367, Remove dead code from the WebCore bindings and 20 Rust crates #40525, and Remove dead code from the inspector protocol package, bun_jsc, bun_install, and the Windows named pipe modules #40557 touch different hunks.
• CI: build 107283 had one red lane, test/js/web/fetch/fetch-leak.test.ts (an RSS threshold missed by under 1 MB; test(fetch-leak): keep the RSS leak thresholds clear of measurement noise #37209 tracks that test's noise). The retriggered build 107290 passed 181 of 182 jobs; the one red lane is test/js/web/url/url.test.ts on darwin x64, which fails the same way on main (ICU version on that host). Both are reported to main-break triage. Everything else passed, on retry or alone.

[robobun]

^{Updated 10:18 PM PT - Aug 27th, 2026}

❌ @robobun, your commit 6d7ad04 has 1 failures in Build #107290 (All Failures):

• test/js/web/url/url.test.ts - code 1: TypeError: Invalid URL on 🍎 any x64

---

🧪   To try this PR locally:

bunx bun-pr 40690

That installs a local version of the PR into your bun-40690 executable, so you can run:

bun-40690 --bun

[claude]

Code review found no issues

No high-confidence issues detected in this change.

[claude]

Code review found no issues

No high-confidence issues detected in this change.