bun_core: delete unused MapLike trait, FieldType marker, EmbedDir

[dylan-conway]

Follow-up to #31536 — removes the remaining unused comptime-reflection placeholders from util.rs plus a few bun_core strays.

cargo check --workspace passes.

Why this code exists

src/bun_core/util.zig is not @imported anywhere in src/**/*.zig (every util import points at runtime/shell/util.zig, node/util/validators.zig, etc.; bun.zig does not re-export it). So everything ported from that file was dead from day one.

Item	Zig original	Zig callers	Status
MapLike trait	none — Zig used comptime duck-typing (Map.KV, @hasField, @FieldType builtin)	n/a	Rust-port artifact (translation of the comptime probes)
Key<M> / Value<M>	src/bun_core/util.zig:3,7	0 — not even used inside util.zig (fromMapLike calls the @FieldType builtin directly)	dead in Zig too
from_entries	util.zig:11 (fromEntries)	0 external — only called by from() at :151,153, which has 0 callers	dead in Zig too
from_map_like	util.zig:80 (fromMapLike)	0 external — only called by from() at :139	dead in Zig too
FieldType enum	util.zig:101 (a fn → ?type)	0 external — all grep hits are the Zig builtin @FieldType or unrelated SQL enums	dead in Zig too (and obsoleted by Zig's builtin @FieldType)
EmbedDir	none — neither EmbedDir nor EmbedKind exist in *.zig	n/a	Rust-port artifact (alias for an alternate Rust-side spelling)
buffered_reader_size	src/bun_core/deprecated.zig:47 (bufferedReaderSize)	0	dead in Zig too
auto_format_label / _fallback	deprecated.zig:639,631	2 — src/runtime/node.zig:342, src/runtime/test_runner/expect.zig:122	Zig callers' Rust ports use native Display/Debug instead of comptime format-label dispatch
PathString::USE_SMALL_PATH_STRING	src/string/PathString.zig:12 (pub const use_small_path_string)	0 — PathString.zig only reads the file-private use_small_path_string_ (:2); the pub re-export has no consumers	dead in Zig too (the public const; the private backing value is still load-bearing)

Also updates the stale port-note comment in bundler/options.rs that pointed at the deleted MapLike.

[robobun]

^{Updated 11:05 PM PT - May 28th, 2026}

❌ @dylan-conway, your commit d8e76b3 has some failures in Build #58843 (All Failures)

---

🧪   To try this PR locally:

bunx bun-pr 31543

That installs a local version of the PR into your bun-31543 executable, so you can run:

bun-31543 --bun

[coderabbitai]

Walkthrough

This PR removes or simplifies several public APIs across core modules: the deprecated buffered_reader_size is replaced with a fixed-size buffered_reader variant; auto_format_label utilities and PathString::USE_SMALL_PATH_STRING are removed; generic map construction helpers (MapLike, from_entries, from_map_like) and FieldType are deleted from util.rs; and EmbedDir type alias is removed. Related comments in bundler/options.rs are updated accordingly.

Changes

API Surface Cleanup and Removal

Layer / File(s)	Summary
Deprecated module API simplification src/bun_core/deprecated.rs	buffered_reader_size<const SIZE> generic constructor is replaced with fixed-size buffered_reader returning BufferedReader<4096, R>; auto_format_label_fallback and auto_format_label functions are removed; RapidHash is re-exported from bun_hash to preserve the crate::deprecated::RapidHash resolution path.
PathString public constant removal src/bun_core/string/PathString.rs	Public associated constant PathString::USE_SMALL_PATH_STRING is removed; internal USE_SMALL_PATH_STRING_ flag continues to control pointer bit width.
Util module public API removals src/bun_core/util.rs	MapLike trait, Key/Value type aliases, from_entries and from_map_like constructors, and FieldType placeholder enum are deleted; EmbedDir type alias is removed leaving only EmbedKind for embed-root selection; needsAllocator comment block is deleted.
Comment updates reflecting API removals src/bundler/options.rs	PORT NOTE comments are updated to remove references to MapLike/from_entries capacity behavior and clarify monomorphization to concrete LoaderHashTable type.

Possibly related PRs

• oven-sh/bun#31536: Removes ArrayLike and related Vec<T> implementations from src/bun_core/util.rs, continuing the removal of generic ported helper traits and constructors alongside this PR's MapLike deletion.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly matches the main change: removing the MapLike trait, FieldType marker, and EmbedDir from bun_core utilities.
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.
Description check	✅ Passed	The PR description provides a detailed explanation of what is being removed and why, with a comprehensive evidence table showing all removed items are genuinely dead code.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

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

[claude]

LGTM — pure dead-code deletion of unused port placeholders.

Extended reasoning...

Overview

Follow-up to #31536. Deletes unused Rust port placeholders from bun_core: the MapLike trait + Key/Value aliases + from_entries/from_map_like helpers, the unconstructible FieldType marker enum, the EmbedDir type alias, buffered_reader_size, auto_format_label/auto_format_label_fallback, the PathString::USE_SMALL_PATH_STRING re-export const, the now-orphaned use core::hash::Hash import, and a couple of stale port-note comments in bundler/options.rs. No logic is touched.

Verification

Grepped the full src/ tree (*.rs only) for each removed identifier. Zero references remain. The apparent hits for FieldType/from_entries in the broader grep are unrelated: Zig source files, JSValue::from_entries (different type/method), and doc comments referencing Zig's @FieldType builtin — none import or use the deleted bun_core::util items. USE_SMALL_PATH_STRING_ (the private module const with trailing underscore) remains in PathString.rs and is still used internally; only the never-read public re-export was removed.

Security risks

None. Pure deletions of code with zero callers and zero impls; no runtime behavior, auth, crypto, or I/O paths affected.

Level of scrutiny

Low. Mechanical dead-code removal in port-scaffolding modules (deprecated.rs, util.rs). The compiler is the proof here — cargo check --workspace passes, and Rust would fail the build if any of these were referenced. The bundler/options.rs change is comment-only.

Other factors

No prior reviewer comments to address. Bug-hunting system found nothing. Same shape as the already-merged #31536 (ArrayLike removal).