[2.0 rc.15 / next] GRAPH_GROWTH reports a keyed cache filling with new keys as a leak, and a cache has no way to say what it is #4035

Summary

A cache that keeps entries by key reports GRAPH_GROWTH when visits fill it with new keys, and the message says a visit left a createRoot() behind with no dispose. This is the usual shape of a data layer's entity cache: one entry per item, each under its own root so it can be evicted, all under the cache's long-lived root. Since #4020 (fixing #4007), a series must also climb in what outlived each navigation, but a cache's entries are alive when the next navigation starts and survive it, exactly as a leaked root would. Nothing in the graph's shape tells a cache filling up from a leak, and there is no way for the cache to say what it is. OBSERVE.exclude is meant for an observer's own subtree and silences every diagnostic under it, not only this check.

Reproduction

solid-js 2.0.0-rc.15, no DOM. Each visit to /items/:page lists two items the cache hasn't seen; / sits between visits.

import {
  OBSERVE,
  createEffect,
  createMemo,
  createProjection,
  createRenderEffect,
  createRoot,
  createSignal,
  flush,
  getOwner,
  runWithOwner,
} from "solid-js";
import { attribution } from "solid-js/attribution";

const variant = process.argv[2] ?? "A";
attribution.enable({ log: false });
const findings: { route: string; grew: string[] }[] = [];
OBSERVE!.diagnostics.subscribe((event) => {
  if (event.code === "GRAPH_GROWTH") findings.push(event.data as { route: string; grew: string[] });
});

// An entry per item (a signal and a projection of it), each under its own
// root so it can be evicted, all under the cache's root.
const cache = createRoot((dispose) => ({ owner: getOwner()!, dispose }), {
  cache: variant !== "A",
});
const entries = new Map<number, { value: number }>();
const fill = (id: number) =>
  runWithOwner(cache.owner, () =>
    createRoot(() => {
      const [value] = createSignal(id);
      entries.set(
        id,
        createProjection<{ value: number }>(
          (draft) => {
            draft.value = value() * 2;
          },
          { value: 0 },
        ),
      );
    }),
  );

const leaked: (() => void)[] = [];
const app = createRoot((dispose) => {
  const [location, setLocation] = createSignal("/");
  createRenderEffect(
    () => (location(), [...entries.values()].reduce((sum, entry) => sum + entry.value, 0)),
    () => {},
  );
  return { setLocation, dispose };
});
flush();

const navigate = (name: string, to: string, before?: () => void) => {
  OBSERVE!.attribution.withOrigin({ kind: "navigation", name, to }, () => {
    before?.();
    app.setLocation(to);
  });
  flush();
};
for (const page of [1, 2, 3]) {
  navigate("/items/:page", `/items/${page}`, () => {
    fill(page * 2 - 1);
    fill(page * 2);
    if (variant === "C")
      runWithOwner(null, () =>
        createRoot((dispose) => {
          leaked.push(dispose);
          const [n] = createSignal(0);
          createEffect(n, () => {});
          createMemo(() => n() + 1);
        }),
      );
  });
  navigate("/", "/");
}
console.log(variant, findings);

Run with node --conditions=browser --conditions=development repro.ts <A|B|C>.

Without the fix the option doesn't exist, so B is the same as A.

Cause

walkGraph (packages/signals/src/core/attribution.ts) counts every node alive at a navigation's start and still alive at its settle as survived, whoever owns it. Projections also record no owner: createStore puts its owner in storeOwners, and store property nodes are stamped from it, but createProjection doesn't, so a projection's property nodes have none.

Expected

A cache can declare itself, and what it keeps is left out of what survived, while a leak beside it still reports. Related: #4007, #4020.

Possible fix

Let a root say it is a cache: createRoot(fn, { cache: true }) (and createOwner). Observe tiers set a config bit for it, as they do for CONFIG_WIDE and CONFIG_SUPERSEDES, and prod ignores the option. walkGraph then leaves out of survived what such a root keeps: the owners and computations under it, and the signals created there (_owner). The whole-graph counts (graphSize()) are unchanged. createProjection records the owner in scope in storeOwners, as createStore does, so the stores and projections a cache keeps are left out too, and their attribution owner paths become complete as well.

Tested on the RC.15 release commit (ea4438b; next at 9f4174b has no signals changes since): the signals suite passes with it (5,212 tests, 20 expected failures, 2 skipped; 5,209 without it). Three new graph-growth tests cover a declared cache staying quiet, the same cache undeclared still reporting, and a leak beside a declared cache still reporting. The two declared-cache tests fail without the change, and the first one also fails when only the projection's owner isn't recorded.

(submitted by Claude Opus 5.5 on behalf of rvlzzr)