Remove dead code from bun_collections, bun_io, and bun_react_compiler

[robobun]

Problem

• A few pub Rust items have no caller on any platform outside of unit tests. dead_code does not see them because they are pub, and the Linux-only unused_pub lint cannot tell them apart from items that Windows or macOS code uses.
• PosixStreamingWriterParent::on_ready (src/io/PipeWriter.rs) is a trait slot that PosixStreamingWriter never dispatches. Both parents (FileSink, Terminal) already detect the drained transition in on_write.

Fix

• bun_collections::static_hash_map::HashMapMixin: remove slice, put_assume_capacity, get, delete. The one implementor is StaticHashMap; the one external user (install/lockfile.rs) calls only get_or_put_assume_capacity and has_with_hash. The unit test now goes through those.
• bun_react_compiler::hir::environment::Environment: remove new and get_property_type. Production code uses with_config and the private get_property_type_from_shapes; the unit tests now call those.
• bun_io: remove PosixStreamingWriterParent::on_ready, the POSIX arm of impl_streaming_writer_parent! that forwarded it, and the Terminal override. FileSink::on_ready now only backs the Windows on_writable slot, so it is #[cfg(windows)]. mordant-baseline.toml drops the entries these removals clear.
• src/runtime/image/backend_coregraphics.rs: remove 14 stale #[allow(dead_code)] escapes. The module is compiled only under cfg(target_os = "macos") and every item is reachable there in dev and release, so the escapes suppress nothing. test/internal/source-lints/dead-code-escape-limits.json is regenerated to match.
• Verified: cargo check -p bun_runtime on linux-x64, bun scripts/rust-check-all.ts x86_64-pc-windows-msvc aarch64-apple-darwin (plus x86_64-apple-darwin and --release for the CoreGraphics file), dead-code-escapes.test.ts (fails on the base tree, passes here), cargo test -p bun_collections static_hash_map, bun bd, then terminal.test.ts, spawn-stdin-readable-stream-integration.test.ts, bun-write.test.js, and the trusted-dependency tests in bun-install-lifecycle-scripts.test.ts.

Background

• StaticHashMap is a fixed-capacity Robin Hood table (port of rheia's hash_map.zig). Bun uses one instance: the default trusted-dependencies set in the lockfile.
• impl_streaming_writer_parent! stamps the POSIX and Windows parent vtables for a streaming pipe writer from one list of handler names. Only the Windows writer has a writable callback (on_writable); the on_ready = ... argument still feeds that.

Notes

How the candidates were found: the unused_pub findings recorded in mordant-baseline.toml (416 items) were each checked for references under every cfg (windows, macos, freebsd, test, bun_codegen_embed). Almost all of them are live on another platform, which is why they stay in the baseline. The items above are the ones with no caller anywhere. Every removal was also checked against the diffs of the open dead-code PRs so nothing here duplicates them.

Other scans that came back empty or already covered by open PRs: Rust files outside every module tree, macro_rules! with no invocation, trait methods with no call site, enum variants and struct fields never named, Cargo dependencies never imported, internal JS modules never required, unused exports of src/js/internal/*, builtins in src/js/builtins/* with no C++ or JS reference, C++ extern "C" definitions with no Rust or WebKit caller, and a -Wunused-function -Wunused-member-function -Wunused-template pass over every non-vendor C++ translation unit (the build passes -Wno-unused-function, so these are normally silent). The last two found about 70 symbols, all of which #40232, #40294, #40367, #40492 or #40915 already remove.

Probably dead, left alone on purpose:

• Connection::{begin_header_block, encode_header, send_header_block, send_data, send_push_promise} in src/runtime/api/bun/h2/connection.rs are test-only today, but the module is marked as an in-progress rewrite with #![allow(dead_code)].
• JsClass::estimated_size default body: no generated thunk can reach it (the trait is not in scope in generated_classes.rs), but its doc describes it as the intended fallback.
• bun_jsc::host_fn::host_fn_this_value: no generated caller today, but generate-classes.ts still emits it for a passThis class without sharedThis.
• bun_sys::O::{NOATIME, DSYNC, SYMLINK, NOFOLLOW_ANY}, bun_sys::posix::{R_OK, POLL_OUT}: unused on every platform, kept for flag-table completeness.

[robobun]

^{Updated 12:38 AM PT - Sep 9th, 2026}

✅ @robobun, your commit 2e07343f8631aac33795bdb9a64e9a7964ea8257 passed in Build #113498! 🎉

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🧪   To try this PR locally:

bunx bun-pr 42119

That installs a local version of the PR into your bun-42119 executable, so you can run:

bun-42119 --bun

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Walkthrough

The PR removes unused HashMapMixin and Environment APIs, updates tests and lint baselines, removes obsolete CoreGraphics dead-code suppressions, and changes POSIX writer drain detection to use on_write.

Changes

Unused public API and lint cleanup

Layer / File(s)	Summary
Hash map API reduction src/collections/StaticHashMap.rs, mordant-baseline.toml	HashMapMixin removes slicing, insertion, lookup, and deletion helpers. Stress tests use the remaining probing APIs.
Environment API reduction src/react_compiler/hir/environment.rs, mordant-baseline.toml	Environment::new and the public property lookup method are removed. Tests use with_config and the shape-registry helper.
CoreGraphics dead-code cleanup src/runtime/image/backend_coregraphics.rs, test/internal/source-lints/dead-code-escape-limits.json	Dead-code suppression attributes and the related lint escape entry are removed.

POSIX writer callback cleanup

Layer / File(s)	Summary
Streaming writer callback contract src/io/PipeWriter.rs, mordant-baseline.toml	POSIX streaming writer parents no longer define or generate on_ready.
POSIX drain handling src/runtime/api/bun/Terminal.rs, src/runtime/webcore/FileSink.rs	POSIX drain detection moves to on_write. FileSink::on_ready is compiled only on Windows.

Suggested reviewers: jarred-sumner

Priority: ⬇️ Low

Merge Risk: 🟡 Moderate · up to 2e073

The cleanup retains POSIX terminal drain handling through on_write, but an EOF path may leave buffered terminal state and callbacks retained. Resolve or explicitly accept this behavior before merge.

🚥 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 summarizes the primary change: removing unused Rust code from bun_collections, bun_io, and bun_react_compiler. It omits some secondary cleanup, but it is specific and accurate.
Description check	✅ Passed	The description explains the problem, fixes, affected components, background, and verification steps. It does not use the template headings exactly, but it provides the required information in equival…

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@src/runtime/api/bun/Terminal.rs`:
- Line 1771: Update the POSIX WriteStatus::EndOfFile handling in
Terminal::on_write to clear writer_has_buffered before continuing EOF cleanup.
Do not call on_writer_ready for EOF; reserve that notification for Drained,
while preserving the existing POSIX streaming-writer behavior.

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• mordant-baseline.toml
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• src/io/PipeWriter.rs

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[robobun]

On the Terminal::on_write note: the POSIX EndOfFile handling is unchanged by this PR. The hunk only rewords the comment on that line, because the on_ready slot it referred to no longer exists. Whether a write-side EOF with buffered data should also clear writer_has_buffered on POSIX (as the Windows arm does) is a behavior question about existing code, so I am keeping it out of this dead-code removal and tracking it separately.

[claude]

LGTM — mechanical dead-code removal with no behavioral change on any platform.

What was reviewed:

• Grepped for remaining callers of every removed item (HashMapMixin::{slice,put_assume_capacity,get,delete}, PosixStreamingWriterParent::on_ready, Environment::{new,get_property_type}) across all cfg branches — none found; the sole StaticHashMap consumer in install/lockfile.rs uses only the surviving methods.
• Checked the impl_streaming_writer_parent! macro: the $on_ready matcher still feeds Windows on_writable (line 2707), and both invocations (FileSink, WindowsNamedPipe) still pass it; FileSink::on_ready is correctly reachable only from that Windows arm now that it's #[cfg(windows)].
• Terminal::on_writer_ready remains live via on_write (POSIX) and on_writable (Windows), so removing the never-dispatched POSIX on_ready override orphans nothing.
• StaticHashMap test rewrite: fresh boxed map per seed is equivalent to the prior delete()-drained reuse; remaining get_or_put_assume_capacity/has_with_hash are still fully exercised at 100% load.

Extended reasoning...

Overview

This PR removes public Rust items that the unused_pub lint flagged in mordant-baseline.toml and that have no caller on any platform: four HashMapMixin trait methods in src/collections/StaticHashMap.rs, the never-dispatched PosixStreamingWriterParent::on_ready trait slot and its macro forwarding arm in src/io/PipeWriter.rs, the corresponding Terminal override, Environment::{new, get_property_type} in the React compiler HIR, and gates FileSink::on_ready behind #[cfg(windows)]. Unit tests are rewritten to exercise the surviving surface directly, and the mordant baseline is decremented to match.

Security risks

None. This is pure dead-code deletion plus test/comment adjustments; no input parsing, auth, crypto, or network paths are touched, and no runtime behavior changes on any platform.

Level of scrutiny

Moderate, focused on the two things that make dead-code removal risky: cfg-gated callers the Linux lint can't see, and macro expansions. I verified both by grep. PosixStreamingWriter genuinely never dispatches on_ready (no call sites in PipeWriter.rs outside the macro matcher and the Windows on_writable expansion). The $on_ready matcher token is still consumed by the Windows arm at line 2707, so both macro invocations (FileSink.rs:150, WindowsNamedPipe.rs:1156) remain well-formed on all targets. Terminal implements the trait by hand rather than via the macro, and its on_writer_ready helper stays live through three other call sites. get_property_type_from_shapes is the existing private helper the removed wrapper delegated to, so the test rewrite exercises the same code path production uses.

Other factors

The PR description explicitly names every deletion and lists cross-target verification (rust-check-all on x86_64-pc-windows-msvc and aarch64-apple-darwin, plus the relevant test files), satisfying REVIEW.md's "delete dead code in the same PR that makes it dead — name the deletions" and cross-platform requirements. The StaticHashMap test change is a justified narrowing (coverage for deleted methods removed; a fresh map per seed is equivalent starting state to the prior delete-drained reuse). Updated comments describe the code as it now is without narrating the change. No CODEOWNERS entries cover the touched files, and there are no outstanding third-party reviews on the timeline.

[claude]

Code review found no issues

No high-confidence issues detected in this change.