[robobun]

Problem

• The tree bun install writes is not always the tree the next bun install builds from that file. Repro with three dependencies, no lockfile from an older Bun involved: next + postcss-loader, then bun add -d vite, then a plain bun install with nothing changed prints 2 packages installed, moves node_modules/postcss from 8.4.31 to 8.5.26 (8.4.31 now under next/node_modules), and leaves bun.lock untouched, still keyed with 8.4.31 at the root. A later unrelated bun add then flips the postcss keys in the lockfile diff. With the isolated linker the same second install re-keys the postcss-loader store entry instead.
• This is also what the 1.3 to 1.4 ledger entry is seeing (same bun.lock, 1.3.14 installs 8.4.31 at the root, 1.4 installs 8.5.26): the 1.3 lockfile records a tree built from a peer binding that 1.4 no longer reproduces on load, see Background.
• Cause: since install: fix stale global-store links on disable and peer edge drift across bun.lock loads #32182, loading bun.lock binds a required ranged peer edge (postcss-loader -> postcss@^7 || ^8.0.1) to the highest satisfying version in the file (bun.lock.rs, resolve_peer_dep_version_based). Nothing applies that rule when the tree is written: the resolver leaves the edge on whatever satisfied it when it was resolved, an install on top of an existing lockfile keeps the binding it loaded (Package::clone copies it, get_or_put_resolved_package returns early on a bound edge) even when this install adds a higher version, and the package-lock.json / yarn.lock migrations bind to whatever the other tool had installed. The first load after such a write moves the edge.
• The binding decides placement because the hoister (Tree.rs, process_subtree) places whatever a peer edge points at, and root devDependencies hoist before dependencies (Behavior::cmp), so a dev tool's peer edge usually decides which version of a package sits at the root of node_modules. The lockfile is not rewritten because the save check (Lockfile::eql in install_with_manager.rs) compares the loaded tree with the cleaned tree, both built from the rebound edge.

Fix

• The hoister binds every peer edge it processes (Tree.rs, Builder::bind_peer, called at the top of the per-dependency loop in process_subtree) with the loader's own resolve_peer_dep_version_based, before the edge is filtered, placed or deduped. Every tree goes through this one place: the tree built after loading bun.lock, the one clean builds for saving and installing (every install, add, remove, update), the one the install pass filters, and the ones the package-lock.json / yarn.lock / pnpm-lock.yaml migrations build. So whatever bindings the edges arrive with, the tree built from a given set of packages is the same, and it is the tree a reload of the saved file rebuilds. Edges the loader leaves on the tree walk (optional peers, * ranges, overridden names) return None from the shared helper and are left alone, so the exemptions stay in one place; the loader itself is unchanged. (The first version of this PR ran a separate pass before hoisting from two call sites; review asked for it to live in the hoister.)
• yarn.rs: hoisting now consults package_index, and the yarn.lock migration was the one lockfile builder that did not index packages by name: it put one version of each name under the name and the others under synthetic keys (name#id, parent/name, name@version, alias names) that nothing ever looked up, plus a usage count nothing read. It now indexes every package under its own name the way bun.lockb loading and the npm / pnpm migrations do (about 210 lines replaced by a 4-line loop). The migrated tree is otherwise unaffected, every yarn snapshot is unchanged, and a side effect is that dedupe lookups during the install that migrates now see all versions, as they do after any other load.
• verify_data (debug builds) checks that every package is in package_index under its own name, so a builder that stops indexing fails the install suites instead of mis-binding peers.
• Correct because the loader's rule is what every later install applies anyway; binding in the hoister just makes the install that writes the file apply it too, so the tree it writes and installs is the fixed point. It also removes the dependence of these edges on manifest arrival order, since the binding is derived from the finished package set. Cost: a package_index lookup per peer edge per tree build; non-peer edges pay one flag test.
• Tests (each fails on main without the src/ changes, passes with them):
  • test/cli/install/hoist.test.ts: hoisted linker, the bun add sequence above with registry fixtures; the reinstall must be a no-op, the layout and bun.lock must match, and a fresh resolve of the same package.json must write the same lockfile. On main the reinstall prints 2 packages installed.
  • test/cli/install/isolated-install.test.ts: same sequence, the store entry must be re-keyed by the install that adds the version, not the next one, and the project link must point at the rebound variant. On main the reinstall prints + peer-deps-fixed@1.0.0.
  • test/cli/install/migration/migrate.test.ts: a package-lock.json where npm satisfied the peer with the lower hoisted version migrates to the same packages a fresh resolve writes. On main the migrated root key is the lower version.
  • test/cli/install/migration/yarn-lock-migration.test.ts: a yarn.lock whose foo@^1.0.0 spec resolved to the 1.0.0 it lists first while 1.5.0 is also in the graph migrates with 1.5.0 at the root (1.0.0 nested under its exact dependent). On main it keeps yarn's 1.0.0 at the root and nests 1.5.0, a tree the first reload then rebuilds differently.
  • Ran locally with the change: isolated-install, bun-install-registry, bun-lock, bun-lockb, bun-workspaces, catalogs, bun-dedupe, bun-prune, bun-audit, bun-update, bun-update-transitive, bun-add, bun-add-catalog, bun-add-filter, bun-remove, bun-patch, overrides, nested-overrides, frozen-lockfile-pruned, public-hoist-pattern, bun-pm-why, lockfile-only, lockfile-version-2, bun-update-lockfile-sync, isolated-relink, migrate-bun-lockb-v2 and every migration suite, all green with every snapshot unchanged. bun-install.test.ts and complex-workspace.test.ts fail identically here without the change (gitlab/bitbucket and other external hosts are blocked in this environment).

Background

• bun.lock stores packages keyed by the node_modules path the hoister chose, and stores no explicit target for peer edges. On load, ordinary edges are resolved by walking up those keys; since install: fix stale global-store links on disable and peer edge drift across bun.lock loads #32182 required ranged peer edges are instead bound by version, because the key walk rebound them to whatever was hoisted above them, which re-keyed isolated store entries (whose names hash the peer bindings) on every warm install.
• The hoister is breadth-first over the dependency graph: a package is placed as high as possible, and the first edge to reach a directory for a given name wins it; later edges to other versions nest under their dependents. A peer edge whose range is satisfied by what is already placed above it places nothing, so the peer's binding is only visible in the tree when its dependent is processed before the other dependents, which is exactly the dev tool case (postcss-loader, vite plugins, eslint plugins).
• Upgrade impact: a lockfile written by this branch produces the same hoisted tree under 1.3 and 1.4 (1.3 finds the bound version at the path where this branch placed it). The ledger's divergence exists only for lockfiles whose recorded tree reflects a lower binding; 1.3 wrote those depending on resolve timing and install history (a fresh 1.3.14 install of the ledger's package.json here put 8.5.26 at the root, the ledger's run put 8.4.31 there), and this branch never writes one. Such a lockfile is still installed deterministically by 1.4 and its keys are corrected by the next install that saves; a plain bun install that only loads it does not rewrite it, since the save check compares trees built from the same bindings. Making that case re-save on load is possible but is left out of this change.
• Related open work: install: resolve deferred * peers after their siblings, not on arrival order #37713 (* peers), install: let the hoister bind optional peers when loading bun.lock #37925 (optional peers) and install: keep a peer nothing in bun.lock satisfies where the file records it #38892 (the nothing-satisfies fallback) change which edges the loader binds by version or what they bind to; because the hoister calls the same helper, the written tree follows whatever rule the loader ends up with, and the only textual overlap with install: keep a peer nothing in bun.lock satisfies where the file records it #38892 is the two doc-comment lines added to that helper here.

Real-world sequences (registry, bun 1.3.14 vs main, this machine)

# next@14.2.5 + postcss-loader@^8.1.1 (dev), main build
bun install                    # root postcss 8.4.31
bun add -d vite@^5.3.3         # root 8.4.31, vite/node_modules/postcss 8.5.26, bun.lock keys agree
bun install                    # "2 packages installed": root 8.5.26, next/node_modules/postcss 8.4.31, bun.lock unchanged
bun add -d is-odd              # bun.lock diff now also moves "postcss" -> 8.5.26 and "vite/postcss" -> "next/postcss"

# same sequence with bun 1.3.14: root stays 8.4.31 throughout, no re-links, is-odd diff touches nothing else

# ledger's 836-package package.json, lockfile shaped "postcss" = 8.4.31, "vite/postcss" = 8.5.26
1.3.14 install --frozen-lockfile   # root 8.4.31
main   install --frozen-lockfile   # "2 packages installed", root 8.5.26 + next/node_modules/postcss
1.3.14 install --frozen-lockfile   # "1 package installed", root 8.4.31
# with the lockfile shaped "postcss" = 8.5.26, "next/postcss" = 8.4.31 (what a fresh 1.3.14 install wrote here,
# and what this branch writes) both versions report "no changes" over each other's tree.

---

no test proof · iteration 8 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/cli/install/isolated-install.test.ts test/cli/install/migration/migrate.test.ts

[robobun]

Status: ready for review at c86767d (squashed onto current main after a conflict with #39324; the conflict was inside the yarn.rs block this PR deletes, plus its import line, so the deletion stands). Waiting on CI for the rebased commit.

Reproduced on a main release build with next + postcss-loader, bun add -d vite, then a plain bun install: the reinstall prints 2 packages installed and moves the root postcss while bun.lock stays byte-identical. Also reproduced the ledger ping-pong on its 836-package project between bun 1.3.14 and main with a lockfile keyed postcss = 8.4.31 / vite/postcss = 8.5.26.

Current shape (after @dylan-conway's comment): the hoister binds each peer edge as it processes it, so every tree build agrees with bun.lock loading; the yarn.lock migration now indexes packages by name so hoisting can rely on package_index there too. The hoisted, isolated, package-lock.json and yarn.lock tests all fail on main and pass with the change; the install and migration suites pass locally on the rebased commit. All review threads are resolved.

The previous run (build 97732, same diff) was green on 177 jobs; its one failure was the x64-asan lane on test/regression/issue/09041.test.ts, a shell stdin-redirect use-after-free unrelated to this change, reported separately.

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---

Walkthrough

Changes

The lockfile resolver now binds ranged peer dependencies through Bun lockfile resolution before repeated hoisting. Tests cover hoisted and isolated installs, repeated reinstalls, lockfile regeneration, and npm migration parity.

Ranged peer rebinding

Layer / File(s)	Summary
Peer binding before hoisting src/install/lockfile.rs	Lockfile::resolve resolves peer versions before hoisting and repeats hoisting until stable.
Install and migration regression coverage test/cli/install/hoist.test.ts, test/cli/install/isolated-install.test.ts, test/cli/install/migration/migrate.test.ts	Tests verify peer rebinding, package layouts, no-op reinstalls, lockfile consistency, and migration parity.

Possibly related PRs

• oven-sh/bun#30855: Both modify peer-dependency resolution and hoisting for satisfying version ranges.
• oven-sh/bun#37426: Both update Lockfile::resolve hoisting and peer binding for different peer cases.
• oven-sh/bun#37713: Both modify peer version resolution and deterministic rebinding.

Suggested reviewers: jarred-sumner

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Title check	✅ Passed	The title clearly identifies the main change: binding peer edges during hoisting using the lockfile loading rule.
Description check	✅ Passed	The description explains the problem, fix, scope, exemptions, tests, and verification results in substantial detail.

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In `@test/cli/install/isolated-install.test.ts`:
- Around line 1261-1263: Strengthen the assertions around the filtered
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[robobun]

^{Updated 2:02 AM PT - Aug 17th, 2026}

✅ @robobun, your commit c86767db2f2a0f10d8cb70f1d861bc5159ab33f6 passed in Build #99930! 🎉

---

🧪   To try this PR locally:

bunx bun-pr 38767

That installs a local version of the PR into your bun-38767 executable, so you can run:

bun-38767 --bun

[claude]

The yarn.lock migration concern from my earlier review is addressed — the pass now lives in Cloner::flush and the npm migration only, resolve() is back to just the hoist loop, and every_package_is_indexed_by_name asserts the precondition in debug builds. No further issues found this pass.

Because this changes which version a ranged peer edge binds to before hoisting on every install path, and therefore which copy lands at the root of node_modules, a human familiar with the install/hoist subsystem should still sign off.

What was reviewed:

• Confirmed resolve() callers (yarn.rs, pnpm.rs, bun.lock.rs) no longer reach the new pass; pnpm and the bun.lock loader already bind via resolve_peer_dep_version_based themselves.
• Checked the debug assertion covers the yarn synthetic-hash case that broke the first cut; the new yarn test pins the foo@1.0.0-first ordering.
• Checked the four new tests assert the fixed point (reinstall is a no-op, lockfile byte-equal, fresh resolve matches) rather than just the layout.

Extended reasoning...

Overview

Adds Lockfile::bind_peers_like_bun_lock (lockfile.rs, ~30 lines) which walks buffers.dependencies/resolutions and rebinds every peer edge via the existing TextLockfile::resolve_peer_dep_version_based, plus a debug-only every_package_is_indexed_by_name precondition check. Called from two sites: Cloner::flush right before resolve() (every install/add/remove/update) and migrate_npm_lockfile right before its resolve(). Four new tests across hoist.test.ts, isolated-install.test.ts, migrate.test.ts, and yarn-lock-migration.test.ts.

Security risks

None. No untrusted input parsing added; the pass reads already-constructed lockfile buffers and calls an existing resolution helper. No filesystem/network changes.

Level of scrutiny

High. Cloner::flush runs on every install, and the pass changes which package a peer edge points at before the hoister runs — that decides which version of a name sits at the root of node_modules and how bun.lock is keyed. The first cut of this PR had a real bug (rebinding against yarn.rs's synthetic package_index) which I flagged and the author fixed by moving the call out of resolve(); the invariants here are subtle enough that a maintainer who owns the install subsystem should confirm the approach and the upgrade-impact analysis in the PR description.

Other factors

• My prior finding is fully addressed: resolve() is back to a bare hoist loop, the two explicit call sites both build package_index via get_or_put_id, and the debug assertion trips if a future caller violates that. The yarn regression test covers the exact ordering that broke.
• Test coverage is strong for the shape of change: hoisted + isolated linkers, npm migration parity with a fresh resolve, and the yarn guard. The author reports the full install/migration suite passes locally with unchanged snapshots.
• Two comment-cop bot comments remain open on the doc comment at lockfile.rs:1266-1267; robobun replied that it is a one-sentence invariant description, not a workaround justification, which reads correctly to me.
• CI's only failure (test-http-chunk-problem.js) is unrelated and fails on main too per robobun.

[dylan-conway]

peers should bind the same everywhere, not just bun.lock. this seems like a back running this function before hoist. i think it should be hoist itself

[robobun]

Agreed, will move it. Plan: the hoister binds each peer edge as it processes it (in process_subtree, before the edge is placed or deduped), so every tree build (loader, clean, every migration, the filter pass that installs) binds the same way and the pre-pass, its two call sites and the debug assertion go away. That requires the yarn.lock migration to index its packages by name like the other lockfile builders do, since hoisting will then consult package_index on that path too; looking at that now.

[robobun]

@dylan-conway done in a7b557a (HEAD 2febcf5, main merged in). The binding is now in the hoister: Builder::bind_peer runs on each edge at the top of the process_subtree loop, so the loader's tree, the clean tree, the install pass and all three migrations bind peers the same way; resolve is back to the plain hoist loop and the separate pass, its call sites and the assertion are gone. The one thing that needed fixing for that was yarn.rs: it only indexed one version per name under the name and the rest under synthetic keys nothing read, so it now indexes every package under its name like the other builders (net about 210 lines removed; yarn snapshots unchanged), and verify_data checks that invariant in debug builds. The yarn test was changed to the case where yarn's own spec binding and the rule disagree, so it fails on main like the other three. PR description updated to match.

[robobun]

Cross-reference from #38892, which touches the other half of this: the bun.lock loader now keeps a required peer edge on the <dependent>/<peer> entry when the file has one (the hoister prints that entry only when the edge's target conflicts with the version hoisted above it), and runs resolve_peer_dep_version_based only for peer edges without an entry of their own.

bind_peers_like_bun_lock as written here rescans every peer edge, so on a file that has such entries (activepieces/activepieces at HEAD has four, all for ranges nothing in the file satisfies, where the scan falls back to the highest version) it would move those edges at save time. Combined with #38892 the loaded tree and the cleaned tree then differ on those files, which --frozen-lockfile reports as a changed lockfile, and a plain install rewrites them. Whichever of the two lands second needs this pass either to skip edges whose current target is placed in the dependent's own node (the loader's rule), or to accept rewriting those files; the second test group in #38892 (loading bun.lock keeps a peer on the entry printed next to its dependent in bun-lock.test.ts) exercises the shapes.

[robobun]

The yarn.rs part of this PR also fixes a user-visible dedupe bug, reproduced on the released build (1.4.0) and on main, in case it is worth mentioning in the description:

bun add <pkg> in a project that still has a yarn.lock migrates it and then resolves <pkg> against the migrated lockfile in the same run. With the old index shape, a dependency of <pkg> on a package the yarn.lock already locks is not found under its name and a second copy is appended:

• entry keyed "p-alias@npm:pkg-p@^1.0.0", pkg-p@^1.0.0: (yarn sorts the alias spec first), bun add pkg-q where pkg-q depends on pkg-p@^1.0.0: bun.lock gets an extra "pkg-q/pkg-p" copy of pkg-p@1.0.0.
• entry keyed only by the alias spec, adding a package with a peer dependency on pkg-p: the peer is resolved to a fresh pkg-p package instead of the migrated one.
• two locked versions of one name, adding a package that wants the version the old code had filed under a synthetic key: again a nested duplicate.

With this PR's index loop all three dedupe to the migrated package. Three bun add --lockfile-only cases against a loopback registry asserting the full packages object of the resulting bun.lock are in

bun/test/cli/install/migration/yarn-lock-migration.test.ts

Lines 1647 to 1791 in fa524e8

	// `bun add` in a project with only a yarn.lock migrates it and resolves the added package against the
	// migrated lockfile in the same run. Resolution looks locked packages up by package name, so a
	// dependency on a package yarn.lock already locks must reuse the migrated package no matter which
	// specs keyed its yarn.lock entry.
	describe("resolving new dependencies against a migrated yarn.lock", () => {
	const integrity = (fill: number) => "sha512-" + Buffer.alloc(64, fill).toString("base64");
	// The migrated records carry the integrity yarn.lock recorded; anything resolved from the
	// registry in this run carries the registry's. That tells the two apart in bun.lock.
	const lockedP1 = integrity(1);
	const lockedP2 = integrity(2);
	const lockedS = integrity(3);
	const fromRegistry = integrity(9);
	const sha1 = Buffer.alloc(40, "0").toString();
	const yarnEntry = (key: string, name: string, version: string, locked: string, deps = "") =>
	`${key}:
	version "${version}"
	resolved "https://registry.yarnpkg.com/${name}/-/${name}-${version}.tgz#${sha1}"
	integrity ${locked}
	${deps}`;
	const cases: {
	label: string;
	dependencies: Record<string, string>;
	yarnLock: string;
	add: string;
	expected: (registry: string) => Record<string, unknown[]>;
	}[] = [
	{
	// yarn sorts the alias spec first on the shared key line.
	label: "alias spec listed first on the entry's key line",
	dependencies: { "p-alias": "npm:pkg-p@^1.0.0", "pkg-p": "^1.0.0" },
	yarnLock: yarnEntry(`"p-alias@npm:pkg-p@^1.0.0", pkg-p@^1.0.0`, "pkg-p", "1.0.0", lockedP1),
	add: "pkg-q",
	expected: registry => ({
	"p-alias": ["pkg-p@1.0.0", "", {}, lockedP1],
	"pkg-p": ["pkg-p@1.0.0", "", {}, lockedP1],
	"pkg-q": [
	"pkg-q@1.0.0",
	`${registry}pkg-q/-/pkg-q-1.0.0.tgz`,
	{ dependencies: { "pkg-p": "^1.0.0" } },
	fromRegistry,
	],
	}),
	},
	{
	label: "entry keyed only by an alias spec, wanted as a peer dependency",
	dependencies: { "p-alias": "npm:pkg-p@^1.0.0" },
	yarnLock: yarnEntry(`"p-alias@npm:pkg-p@^1.0.0"`, "pkg-p", "1.0.0", lockedP1),
	add: "pkg-r",
	expected: registry => ({
	"p-alias": ["pkg-p@1.0.0", "", {}, lockedP1],
	"pkg-p": ["pkg-p@1.0.0", "", {}, lockedP1],
	"pkg-r": [
	"pkg-r@1.0.0",
	`${registry}pkg-r/-/pkg-r-1.0.0.tgz`,
	{ peerDependencies: { "pkg-p": "^1.0.0" } },
	fromRegistry,
	],
	}),
	},
	{
	label: "second locked version of a name",
	dependencies: { "pkg-p": "^2.0.0", "pkg-s": "^1.0.0" },
	yarnLock: [
	yarnEntry("pkg-p@^1.0.0", "pkg-p", "1.0.0", lockedP1),
	yarnEntry("pkg-p@^2.0.0", "pkg-p", "2.0.0", lockedP2),
	yarnEntry("pkg-s@^1.0.0", "pkg-s", "1.0.0", lockedS, ` dependencies:\n pkg-p "^1.0.0"\n`),
	].join("\n"),
	add: "pkg-t",
	expected: registry => ({
	"pkg-p": ["pkg-p@2.0.0", "", {}, lockedP2],
	"pkg-s": ["pkg-s@1.0.0", "", { dependencies: { "pkg-p": "^1.0.0" } }, lockedS],
	"pkg-s/pkg-p": ["pkg-p@1.0.0", "", {}, lockedP1],
	"pkg-t": [
	"pkg-t@1.0.0",
	`${registry}pkg-t/-/pkg-t-1.0.0.tgz`,
	{ dependencies: { "pkg-p": "^2.0.0" } },
	fromRegistry,
	],
	}),
	},
	];
	const manifests: Record<string, Record<string, object>> = {
	"pkg-p": { "1.0.0": {}, "2.0.0": {} },
	"pkg-q": { "1.0.0": { dependencies: { "pkg-p": "^1.0.0" } } },
	"pkg-r": { "1.0.0": { peerDependencies: { "pkg-p": "^1.0.0" } } },
	"pkg-s": { "1.0.0": { dependencies: { "pkg-p": "^1.0.0" } } },
	"pkg-t": { "1.0.0": { dependencies: { "pkg-p": "^2.0.0" } } },
	};
	test.concurrent.each(cases)("$label", async ({ dependencies, yarnLock, add, expected }) => {
	// `--lockfile-only` below means only packuments are ever requested, never tarballs.
	await using registry = Bun.serve({
	port: 0,
	fetch(req) {
	const name = new URL(req.url).pathname.slice(1);
	const versions = manifests[name];
	if (!versions) return new Response("not found", { status: 404 });
	const entries = Object.entries(versions).map(([version, manifest]): [string, object] => [
	version,
	{
	name,
	version,
	...manifest,
	dist: { tarball: `${registry.url}${name}/-/${name}-${version}.tgz`, integrity: fromRegistry },
	},
	]);
	return Response.json({
	name,
	"dist-tags": { latest: entries.at(-1)![0] },
	versions: Object.fromEntries(entries),
	});
	},
	});
	await using tmpDir = tempDir("yarn-migration-then-add", {
	"package.json": JSON.stringify({ name: "app", dependencies }),
	"yarn.lock": `# yarn lockfile v1\n\n\n${yarnLock}`,
	});
	await using proc = Bun.spawn({
	cmd: [bunExe(), "add", add, "--lockfile-only"],
	cwd: tmpDir,
	env: {
	...bunEnv,
	BUN_CONFIG_REGISTRY: registry.url.href,
	BUN_INSTALL_CACHE_DIR: join(tmpDir, ".bun-cache"),
	},
	stdout: "pipe",
	stderr: "pipe",
	stdin: "ignore",
	});
	const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
	expect(stderr).toContain("migrated lockfile from yarn.lock");
	expect(stderr).not.toContain("error:");
	expect(stdout).toContain("Saved bun.lock");
	expect(exitCode).toBe(0);
	const lock = Bun.JSONC.parse(await Bun.file(join(tmpDir, "bun.lock")).text()) as { packages: unknown };
	expect(lock.packages).toStrictEqual(expected(registry.url.href));
	});
	});

(same yarn.rs change as here, plus the tests; they fail on main and pass with the loop). Feel free to fold them in; I am not opening a separate PR for this since the fix is already here (and in #38878).

[robobun]

Update to the note above: #38892 was reworked and the interaction is gone. It now removes the nothing-satisfies fallback from resolve_peer_dep_version_based (returning None so the caller keeps its record) instead of adding a loader-side rule, so Builder::bind_peer here leaves such edges where the load put them. Verified by applying this PR's src/ on top of #38892: its tests and this PR's tests both pass, and the activepieces lockfile re-saves the same way as with #38892 alone. The only textual overlap is the doc paragraph both add to the helper.

[claude]

I reviewed this PR and found no bugs. Because it changes how the hoister binds every peer edge and replaces yarn.rs's package_index construction, a human sign-off on the final shape (post the rework dylan-conway asked for) would still be worthwhile.

What was reviewed:

• bind_peer in Tree.rs: called before the resolution is read in process_subtree, returns early on non-peers, and leaves the edge alone when resolve_peer_dep_version_based returns None (optional peers, *, overrides) — matches the loader's exemptions.
• yarn.rs index rewrite: the removed synthetic-key entries (name#id, parent/name, name@version, alias hashes, usage_count) had no readers; edges resolve via spec_to_package_id, which is unchanged. get_or_put_id maintains descending Resolution::order so the new loop meets the helper's ordering contract.
• verify_data debug assertion and the borrow pattern in bind_peer (copies ParentRef out; does not touch buffers.resolutions through the shared view).
• The four new tests each pin the round-trip invariant on their path and drain subprocess pipes.

Extended reasoning...

Overview

The PR makes the hoister apply the same peer-edge binding rule that loading bun.lock applies, so the tree an install writes is the tree the next install rebuilds from that file. Concretely: Builder::bind_peer (Tree.rs) calls resolve_peer_dep_version_based on each dependency at the top of process_subtree's per-edge loop, before the edge is filtered, placed, or deduped. Because hoisting now consults package_index on every path, yarn.rs is changed to index every package under its own name (a 4-line loop replacing ~210 lines of synthetic-key bookkeeping that nothing read). A debug assertion in verify_data (lockfile.rs) enforces the index invariant. Four new tests cover the hoisted linker, the isolated linker, package-lock.json migration, and yarn.lock migration.

Security risks

None identified. The change is internal to lockfile tree construction and does not touch validation of untrusted input, path handling, or network code. resolve_peer_dep_version_based was already the loader's rule; this calls it from one more site with data the process itself built.

Level of scrutiny

High. The hoister runs on every bun install/add/remove/update and every migration; a wrong peer binding silently changes which version lands at the root of node_modules. The yarn.rs deletion is large (net −210 lines) and, while the PR states every yarn snapshot is unchanged and CI is green (176/179, the red job is an unrelated shell UAF), a maintainer should confirm the removed synthetic-key machinery was indeed unread. dylan-conway already requested the current shape (binding in the hoister rather than a pre-pass) but has not yet approved the reworked version.

Other factors

The two earlier findings from this reviewer (yarn.rs package_index shape, undrained stdout in the yarn test) were addressed and the threads resolved. The PR notes cross-PR interactions with #38892 (nothing-satisfies fallback) and #37713/#37925 (which edges the loader binds); because bind_peer calls the same helper, changes there flow through automatically, but the merge order matters for the doc-comment overlap. Test coverage is thorough — each test asserts the fixed-point invariant (reinstall is a no-op, migrated packages equals a fresh resolve) rather than just a spot value.

[Jarred-Sumner]

This is Claude (an AI assistant) writing on Jarred's behalf.

Included in #44968.