Fix issue with data leaking inside partial `@defer` or `@stream` boundaries during intermediate results by jerelmiller · Pull Request #13347 · apollographql/apollo-client

jerelmiller · 2026-07-23T04:04:51Z

The big change in this PR is making InMemoryCache incremental-aware for cache reads (though hidden behind an internal symbol that enables it). cache.diff is too naive and classifies in-progress queries with @defer boundaries as partial when @defer data hasn't streamed in. This is a problem for how QueryInfo rereads data after a cache write because it won't apply that data to the returned result unless its fully complete. Field values transformed by cache read functions were therefore not applied to intermediate results in a @defer query.

This issue became glaringly apparent with the introduction of custom scalars in 4.3 (currently unreleased) where we need to apply the parsed field values stored in the cache to intermediate chunks. Without that, the user might encounter runtime crashes when expecting the value to be the parsed type.

#13324 was a first attempt at solving this issue across many cases where read functions/custom scalars weren't applied, but it did not fix the issue where partial data inside a @defer or @stream boundary leaked in intermediate results. It relied on the missing tree to reapply field values from the reread cache.diff, but did not prune partial boundaries.

readFromStore can now properly handle partial boundaries when provided with returnPartialData: true (though only when the hidden flag is provided to ensure backwards compatibility until v5). The complex scenarios where partial data can show up inside defer boundaries (especially with overlapping selections in @defer boundaries) is now properly handled during a cache read.

Summary by CodeRabbit

Bug Fixes
- Prevented incomplete cached data from leaking into network-only incremental query results.
- Improved handling of partial @defer content and incomplete @stream array items.
- Corrected cache result reuse when registered fragments resolve differently across queries.
New Features
- Added richer incremental result states: complete, streaming, partial, and empty.
- Improved tracking of pending deferred and streamed results.
- Expanded cache memory metrics for incremental processing.

…fix isFresh

… other tests

jerelmiller · 2026-07-23T04:42:46Z

-            null
-          : result
-        : null,
+    if (


Note: Many of these changes will be simplified when we get to v5 and can enforce caches to be incremental-aware. To maintain backwards compatibility, we can shift data states around. v5 will also require cache reads to return a dataState which will collapse this further.

jerelmiller · 2026-07-23T04:53:43Z

      ...incrementalResult,
      dataState:
        incrementalResult.data == null ? "empty"
+          // TODO: This is too naive. For stream arrays, this might be complete


I need to re-evaluate if this is still true. I'll make sure to remove once I verify if this is ok.

Re-evaluated and found only one case where it actually was too naive. Fixed in 492337d

jerelmiller · 2026-07-23T04:55:21Z

  return writeWithErrors;
 }
-
-function isStreamingPartial(


Much of this is now folded into readFromStore which does a prune pass similar to this, but handles many more edge cases that this did/could not.

jerelmiller · 2026-07-23T05:01:06Z

      const fragment = fragmentMap && fragmentMap[fragmentName];
      invariant(fragment, `No fragment named %s`, fragmentName);
-      return fragment || null;
+      return fragment;


Spotted this while working on this PR. invariant checks that this is a non-nullish value so no need to fallback to null here.

DaleSeo

Just questions.

…cache-no-partial

@jerelmiller

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to release-4.3, this PR will be updated. ⚠️

⚠️

⚠️ `release-4.3` is currently in **pre mode** so this branch has prereleases rather than normal releases. If you want to exit prereleases, run `changeset pre exit` on `release-4.3`. ⚠️

⚠️

⚠️ # Releases ## @apollo/client@4.3.0-alpha.4 ### Patch Changes - [#13347](#13347) [`7d543d6`](7d543d6) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where `network-only` incremental queries could cause cache data to leak into the emitted result when a `@defer` or `@stream` boundary already had complete data in the cache. Cache data inside pending `@defer` objects and `@stream` arrays are now pruned so that only completed `@defer` or `@stream` boundaries are returned. NOTE: This change only applies to `InMemoryCache` when using `GraphQL17Alpha9Handler`. - [#13329](#13329) [`1d581d2`](1d581d2) Thanks [@AmariahAK](https://github.com/AmariahAK)! - Cache diffs for incomplete queries no longer pay the cost of building a full `MissingFieldError` when the `missing` property is not accessed. The error object is now only constructed when the `missing` property is accessed the first time. This improves performance by avoiding a V8 stack capture when `missing` is ignored entirely. As an additional small performance improvement, `JSON.stringify` is no longer used in the error message on objects whose cache ID is known. `JSON.stringify` is only used for non-normalized objects. - [#13347](#13347) [`7d543d6`](7d543d6) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where partial cache data could leak into intermediate incremental results. This could cause runtime crashes if you relied on the presence of values to determine whether the `@defer` data had streamed in or not. Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

@phryneas

…3360) Followup to #13347 Discussed with @phryneas in person. Instead of conditionally passing in the symbol by having caches opt-in, we pass it unconditionally. Caches that want to take advantage of behavior using that symbol can come talk to us on how to implement against the incremental behavior.  ## Summary by CodeRabbit * **Improvements** * Improved incremental, deferred, and streamed cache diff handling. * Updated cache diff results to provide more consistent data-state information. * Simplified incremental data processing across cache implementations. * **Bug Fixes** * Corrected partial-data and missing-field behavior during streaming and incremental reads. * Preserved compatibility for standard cache diff queries that do not use incremental options.

jerelmiller added 30 commits July 15, 2026 11:54

Remove returnPartialData from execSelectionSet. Break many tests but …

2f71d1d

…fix isFresh

Don't pass handleIncrementalSymbol in executeSelectionSet. Break some…

bb25103

… other tests

Add new tests to check for backwards compatibility

2663016

Change stance on expected reported missing for backwards compat

a869cae

Don't set missing to undefined for empty defer boundary

49e2635

Don't report missing if dataState is streaming

6803142

Handle stripping partial defer boundaries

44e368c

Maintain overlapping fields

0746e8b

Handle deep overlapping sibling fields

585fdfc

Handle arrays in keepFieldsFromFieldMap

55b1916

Handle arrays

baf18d3

Simplify newData value

8bdcc95

Add a state machine to better handle state transitions

76f86d9

Update comment

077ec45

Ensure array impl uses transitionTo

a4b0733

Add a deferPartial dataState

14c6766

Set to partial if streaming state and can't handle incremental

1c7e166

Fix fields stripped out in deferPartial fragments

da1eddf

Add more tests for nested defer

3c5e1ec

Ensure fields are copied when fragment is complete

5baf21d

Add comment

ad817d4

Add more tests for more edge cases

30dd7ae

Switch to keep fields from a field map instead

db50f6a

Add more failing tests for more edge cases in lists

2befed3

Ensure arrays return deferBoundaryResults

2a83af8

Make deferBoundaryResults required

4b28b49

Combine tests that only differ by selection order

f5f1701

Fix differing states on array items in the same selection set

bf98b51

Create a class for DeferBoundaries instead

ba02985

Rename var

27fe8b4

jerelmiller added 2 commits July 22, 2026 22:37

Minor refactor

f9ae6de

Clarify comment

13779ac

jerelmiller commented Jul 23, 2026

View reviewed changes

Fix outdated comment

c13b84a

jerelmiller commented Jul 23, 2026

View reviewed changes

Use object shorthand

92c7b5f

jerelmiller commented Jul 23, 2026

View reviewed changes

jerelmiller added 6 commits July 22, 2026 23:01

Remove unused deferInfoSymbol

fcdcfa9

Inline dirty call

02e5a2c

Adjust comment

7a8684e

Fix no-cache stream/defer case where streaming was incorrectly reported

492337d

Remove unused import

21e89eb

Also check if defer is part of the query for no-cache queries

b8c1edd

DaleSeo approved these changes Jul 23, 2026

View reviewed changes

Comment thread src/cache/inmemory/readFromStore.ts

Comment thread src/cache/inmemory/readFromStore.ts

github-actions Bot added the auto-cleanup 🤖 label Jul 23, 2026

jerelmiller added 4 commits July 24, 2026 12:22

Update comment on constant

e03b60c

Change comment on symbol

c497e04

Merge remote-tracking branch 'origin/release-4.3' into jerel/partial-…

9344108

…cache-no-partial

Strip missing for rules before merge

8291097

DaleSeo approved these changes Jul 24, 2026

View reviewed changes

Clean up Prettier, Size-limit, and Api-Extractor

fec399f

jerelmiller merged commit 7d543d6 into release-4.3 Jul 24, 2026
48 checks passed

github-actions Bot mentioned this pull request Jul 24, 2026

Version Packages (alpha) #13351

Merged

This was referenced Jul 24, 2026

Incorrect dataState/data returned for incremental partial data written to cache with returnPartialData: false #13330

Closed

Minor followup for feedback from incremental cache implementation #13360

Merged

This was referenced Jul 31, 2026

Fix a bad dataState value when an error occurs on a deferred field that bubbles to the defer boundary #13376

Closed

Fix some wrong dataState values with network-only and errorPolicy: "none" queries #13381

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Fix issue with data leaking inside partial `@defer` or `@stream` boundaries during intermediate results - #13347

Fix issue with data leaking inside partial `@defer` or `@stream` boundaries during intermediate results#13347
jerelmiller merged 321 commits into
release-4.3from
jerel/partial-cache-no-partial

jerelmiller commented Jul 23, 2026 •

edited by coderabbitai Bot

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jerelmiller commented Jul 23, 2026 •

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