Cache the theme.json data merged from all origins

[sirreal]

What?

Cache WP_Theme_JSON_Resolver_Gutenberg::get_merged_data() per origin for the request, so repeated calls reuse the merged data. Remove the request caches in gutenberg_get_global_settings() and gutenberg_get_global_styles(), which now read through to the resolver.

Supersedes #81883. Core backport: WordPress/wordpress-develop#14071.

Why?

The accessor cache added in #81889 avoids repeated merges for gutenberg_get_global_styles(), but direct resolver callers still merge on every call. These include block style variations, stylesheets, settings and duotone. Block style variations account for most of the remaining work: one merge per block with an is-style-* class.

Caching in the resolver serves all callers and applies the existing block-registration check to every read. Keeping the accessor cache as well produced no measurable request-time improvement.

How?

The resolver caches each origin separately in $merged. A merged entry in $blocks_cache reuses has_same_registered_blocks(), so a block registered after the first merge discards the cached data, as it already does for the per-origin caches. clean_cached_data() resets $merged and rebuilds $blocks_cache from its own keys. An unknown origin resolves to custom, which the docblock already documents as the fallback.

Each call returns a clone, so callers can modify the result without changing the cache. WP_Theme_JSON_Gutenberg::resolve_variables() relies on that.

The gallery block keeps its per-request static. The static is redundant in the plugin, where the build maps wp_get_global_styles() to the plugin accessor, but WordPress Core has no cache behind the function until the resolver change is backported. Only the comment changes.

Compatibility:

• Theme supports added after the first merge in a request need _gutenberg_clean_theme_json_caches() before they appear in merged data. The wp_theme_json_data_* filters already behaved this way through the per-origin caches. Normally both are registered on after_setup_theme.
• The registration check detects block additions, not removals, as before.
• The removed accessor caches lived in the non-persistent theme_json group, so nothing changes across requests. Their WP_DEBUG bypass only affected the current request.
• backport-changelog/7.2/14071.md lists Try caching gutenberg_get_global_styles #81889 as well, since this PR removes the cache it added and Core's layout support never had the static it removed. The entry for wordpress-develop#13214 is dropped; that PR has nothing left to port.

Performance

Measured on 2026-10-07 on an earlier revision of this branch with the same caching behavior, against trunk 4791f174f20. WordPress 7.2-alpha-64225, WP_DEBUG off, median of 20 requests after one warm-up. Values are total time in get_merged_data() per request, including the first merge.

Page	Trunk	This PR
Twenty Twenty-Three front page	3.59 ms	2.03 ms
Twenty Twenty-Four front page	6.61 ms	1.92 ms
Large post, Twenty Twenty-Four	3.64 ms	1.96 ms
Post with 52 block style variations, Twenty Twenty-Four	12.92 ms	1.92 ms

A separate perf-tool run on WordPress 7.1.3, with three interleaved rounds of 16 samples, reduced median wpTemplate time from 15.73 to 13.49 ms for Twenty Twenty-Three and from 12.04 to 10.86 ms for Twenty Twenty-One. Retaining the accessor cache alongside the resolver cache made no difference beyond run-to-run variation.

Testing Instructions

With built assets and the PHP test environment running:

npm run test:unit:php:base -- --filter 'WP_Theme_JSON_Resolver_Gutenberg_Test|WP_Theme_Json_Test'

Tests cover a separate instance per call, the cached data per origin, modification of the returned instance, late block registration, clean_cached_data(), theme switching, and the accessors reflecting a block registered or theme data changed after a previous call.

Local run on 2026-10-07 at the current head, including Tests_Blocks_Render_Gallery: 77 tests, 253 assertions, passing.

Use of AI Tools

Claude generated the implementation, tests, review fixes and this description under @sirreal's direction, including work with Claude Fable 5.1. Codex edited an earlier description. Human review of the generated code is pending.

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[github-actions]

🤖 PR meta 🤖

🎉 Props

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: sirreal <jonsurrell@git.wordpress.org>
Co-authored-by: tellthemachines <isabel_brison@git.wordpress.org>
Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

Updated as activity occurs, without notifying anyone named here. Add the props-bot label to refresh.

⚡ Performance

Show the results

Client side metrics exclude the server response time.

front-end-block-theme

Metric	a50c228	trunk	% Change
timeToFirstByte	57.05 ms +6.22% -2.8%	58.3 ms +15.35% -4.37%	-2.14%
largestContentfulPaint	96 ms +8.33% -4.17%	100 ms +6% -12%	-4%
lcpMinusTtfb	37.45 ms +19.49% -5.61%	36.65 ms +13.23% -9.55%	2.18%
wpBeforeTemplate	29.86 ms +13.33% -2.55%	29.57 ms +9.5% -4.97%	0.98%
wpTemplate	22.79 ms +5.4% -3.6%	25.54 ms +7.44% -6.26%	-10.77%
wpTotal	53.17 ms +6.86% -2.93%	54.85 ms +13.97% -5.07%	-3.06%
wpMemoryUsage	7.61 MB +0% -0%	7.65 MB +0% -0%	-0.57%
wpDbQueries	17 +0% -0%	17 +0% -0%	0%

front-end-classic-theme

Metric	a50c228	trunk	% Change
timeToFirstByte	48.6 ms +1.95% -3.4%	48.45 ms +4.13% -2.37%	0.31%
largestContentfulPaint	104 ms +3.85% -0%	104 ms +3.85% -0%	0%
lcpMinusTtfb	56.4 ms +3.9% -2.39%	56.1 ms +3.65% -2.94%	0.53%
wpBeforeTemplate	27.73 ms +4.8% -3.75%	26.74 ms +1.68% -3.03%	3.7%
wpTemplate	17.21 ms +3.49% -3.89%	18.31 ms +4.1% -1.04%	-6.01%
wpTotal	45.26 ms +2.01% -3.12%	45.11 ms +4.06% -1.75%	0.33%
wpMemoryUsage	6.24 MB +0% -0%	6.26 MB +0% -0%	-0.36%
wpDbQueries	14 +0% -0%	14 +0% -0%	0%

media-processing

Metric	a50c228	trunk	% Change
mediaProcessingJpeg	411.45 ms +1.57% -1.1%	404.94 ms +0.95% -1.1%	1.61%
mediaProcessingAvif	6110.9 ms +0.43% -0.31%	6077.48 ms +0.12% -0.17%	0.55%
mediaProcessingJpegToAvif	4227.58 ms +0.33% -0.5%	4203.07 ms +0.2% -0.12%	0.58%

media-upload

Metric	a50c228	trunk	% Change
jpegUploadProcessing	1451.97 ms +36.22% -1.39%	1429.3 ms +0.62% -1.3%	1.59%
pngUploadProcessing	210.69 ms +9.53% -13.34%	202.8 ms +10.56% -10.44%	3.89%
largeJpegUploadProcessing	1437.42 ms +0.4% -0.76%	1422.6 ms +0.64% -1.27%	1.04%
multipleImageUploadProcessing	1616.53 ms +10.11% -4.59%	1587 ms +10.57% -1.42%	1.86%

post-editor

Metric	a50c228	trunk	% Change
serverResponse	422.73 ms +4.73% -5.58%	418 ms +3.76% -6.9%	1.13%
firstPaint	204.57 ms +7.96% -16.85%	207.56 ms +11.99% -7.31%	-1.44%
domContentLoaded	1025.84 ms +2.29% -0.62%	1050.11 ms +1.16% -0.59%	-2.31%
loaded	1027.08 ms +2.29% -0.61%	1051.32 ms +1.17% -0.57%	-2.31%
firstContentfulPaint	445.11 ms +1.34% -2.7%	460.53 ms +3.6% -0.89%	-3.35%
firstBlock	2979.96 ms +1.37% -1.07%	2971.41 ms +1.37% -0.57%	0.29%
type	18.41 ms +2.23% -5.98%	18.33 ms +6% -1.96%	0.44%
typeWithoutInspector	17.41 ms +1.55% -0.63%	18.5 ms +1.35% -4.05%	-5.89%
typeWithTopToolbar	22.96 ms +5.84% -2.66%	24.26 ms +5.73% -5.36%	-5.36%
typeContainer	8.75 ms +2.74% -3.54%	8.65 ms +0.92% -5.55%	1.16%
focus	113.91 ms +6.79% -7.22%	108.28 ms +2.84% -4.93%	5.2%
firstFocus	209.68 ms +0% -0%	200.11 ms +0% -0%	4.78%
selectAll	451.75 ms +1.42% -0.62%	423.31 ms +6.42% -0.88%	6.72%
listViewOpen	73.12 ms +8.59% -3.23%	70.38 ms +2.53% -8%	3.89%
inserterOpen	39.33 ms +5.92% -5.9%	40.84 ms +10.68% -13.32%	-3.7%
inserterHover	13.3 ms +3.68% -5.94%	11.78 ms +6.54% -5.26%	12.9%
inserterSearch	9.26 ms +4.54% -7.67%	9.14 ms +2.95% -12.04%	1.31%
loadPatterns	677.55 ms +2.05% -1.74%	649.48 ms +0.53% -2.47%	4.32%
wpTotal	412.81 ms +4.37% -5.85%	407.56 ms +3.85% -7.03%	1.29%
wpMemoryUsage	13.30 MB +0% -0%	13.21 MB +0% -0%	0.69%
wpDbQueries	54 +0% -1.85%	53.5 +0.93% -0.93%	0.93%

site-editor

Metric	a50c228	trunk	% Change
serverResponse	404.11 ms +3.88% -3.36%	412.48 ms +1.75% -4.36%	-2.03%
firstPaint	245.54 ms +6.84% -6.12%	230.09 ms +41.27% -3.63%	6.71%
domContentLoaded	1071.72 ms +0.91% -0.96%	1075.06 ms +1.24% -1.59%	-0.31%
loaded	1072.72 ms +0.92% -0.96%	1076.36 ms +1.21% -1.6%	-0.34%
firstContentfulPaint	441.74 ms +4.52% -2.97%	451.55 ms +1.27% -2.84%	-2.17%
firstBlock	4002.56 ms +0.96% -1.08%	3973 ms +1.33% -1.08%	0.74%
type	18.12 ms +2.21% -4.36%	17.38 ms +9.09% -0.86%	4.26%
navigate	119.45 ms +15.06% -0.59%	112.25 ms +6.94% -2.81%	6.41%
loadPatterns	1252.93 ms +3.71% -7.79%	1176.03 ms +2.35% -2.47%	6.54%
loadPages	1002.46 ms +2.32% -1.79%	1009.12 ms +5.89% -3.73%	-0.66%
wpTotal	394.26 ms +3.99% -3.58%	402.17 ms +1.95% -4.28%	-1.97%
wpMemoryUsage	12.33 MB +0% -0%	12.25 MB +0% -0%	0.58%
wpDbQueries	43 +2.33% -0%	43 +2.33% -0%	0%

_{48923db Run}

🏁 Flaky tests

Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

refuses the drop and uploads nothing in /test/e2e/specs/editor/various/single-file-placeholder-drop.spec.js, passed after 1 failed attempt.

Error: expect(received).toHaveLength(expected)

Expected length: 0
Received length: 2
Received array:  [{"_links": {"about": [{"href": "http://localhost:8889/wp-json/wp/v2/types/attachment"}], "author": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/users/1"}], "collection": [{"href": "http://localhost:8889/wp-json/wp/v2/media"}], "curies": [{"href": "https://api.w.org/{rel}", "name": "wp", "templated": true}], "replies": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/comments?post=264"}], "self": [{"href": "http://localhost:8889/wp-json/wp/v2/media/264", "targetHints": {"allow": ["GET", "POST", "PUT", "PATCH", "DELETE"]}}], "wp:attached-to": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/posts/262", "id": 262, "post_type": "post"}]}, "alt_text": "", "author": 1, "caption": {"rendered": ""}, "class_list": ["post-264", "attachment", "type-attachment", "status-inherit", "hentry", "entry"], "comment_status": "open", "date": "2026-10-09T11:20:16", "date_gmt": "2026-10-09T11:20:16", "description": {"rendered": "<p class=\"attachment\"><a href='http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK-1.png'><img loading=\"lazy\" decoding=\"async\" width=\"10\" height=\"10\" src=\"http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK-1.png\" class=\"attachment-medium size-medium\" alt=\"\" style=\"width:100%;height:100%;max-width:10px;\" /></a></p>
"}, "featured_media": 0, "filename": "10x10_e2e_test_image_z9T8jK-1.png", "filesize": 80, "guid": {"rendered": "http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK-1.png"}, "id": 264, "link": "http://localhost:8889/?attachment_id=264", "media_details": {"file": "2026/10/10x10_e2e_test_image_z9T8jK-1.png", "filesize": 80, "height": 10, "image_meta": {"alt": "", "aperture": "0", "camera": "", "caption": "", "copyright": "", "created_timestamp": "0", "credit": "", "focal_length": "0", "iso": "0", "keywords": [], "orientation": "0", "shutter_speed": "0", "title": ""}, "sizes": {}, "width": 10}, "media_type": "image", "meta": [], "mime_type": "image/png", "modified": "2026-10-09T11:20:16", "modified_gmt": "2026-10-09T11:20:16", "ping_status": "closed", "post": 262, "slug": "10x10_e2e_test_image_z9t8jk-2", "source_url": "http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK-1.png", "status": "inherit", "template": "", "title": {"rendered": "10x10_e2e_test_image_z9T8jK"}, "type": "attachment"}, {"_links": {"about": [{"href": "http://localhost:8889/wp-json/wp/v2/types/attachment"}], "author": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/users/1"}], "collection": [{"href": "http://localhost:8889/wp-json/wp/v2/media"}], "curies": [{"href": "https://api.w.org/{rel}", "name": "wp", "templated": true}], "replies": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/comments?post=263"}], "self": [{"href": "http://localhost:8889/wp-json/wp/v2/media/263", "targetHints": {"allow": ["GET", "POST", "PUT", "PATCH", "DELETE"]}}], "wp:attached-to": [{"embeddable": true, "href": "http://localhost:8889/wp-json/wp/v2/posts/262", "id": 262, "post_type": "post"}]}, "alt_text": "", "author": 1, "caption": {"rendered": ""}, "class_list": ["post-263", "attachment", "type-attachment", "status-inherit", "hentry", "entry"], "comment_status": "open", "date": "2026-10-09T11:20:16", "date_gmt": "2026-10-09T11:20:16", "description": {"rendered": "<p class=\"attachment\"><a href='http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK.png'><img loading=\"lazy\" decoding=\"async\" width=\"10\" height=\"10\" src=\"http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK.png\" class=\"attachment-medium size-medium\" alt=\"\" style=\"width:100%;height:100%;max-width:10px;\" /></a></p>
"}, "featured_media": 0, "filename": "10x10_e2e_test_image_z9T8jK.png", "filesize": 80, "guid": {"rendered": "http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK.png"}, "id": 263, "link": "http://localhost:8889/?attachment_id=263", "media_details": {"file": "2026/10/10x10_e2e_test_image_z9T8jK.png", "filesize": 80, "height": 10, "image_meta": {"alt": "", "aperture": "0", "camera": "", "caption": "", "copyright": "", "created_timestamp": "0", "credit": "", "focal_length": "0", "iso": "0", "keywords": [], "orientation": "0", "shutter_speed": "0", "title": ""}, "sizes": {}, "width": 10}, "media_type": "image", "meta": [], "mime_type": "image/png", "modified": "2026-10-09T11:20:16", "modified_gmt": "2026-10-09T11:20:16", "ping_status": "closed", "post": 262, "slug": "10x10_e2e_test_image_z9t8jk", "source_url": "http://localhost:8889/wp-content/uploads/2026/10/10x10_e2e_test_image_z9T8jK.png", "status": "inherit", "template": "", "title": {"rendered": "10x10_e2e_test_image_z9T8jK"}, "type": "attachment"}]
    at /home/runner/work/gutenberg/gutenberg/test/e2e/specs/editor/various/single-file-placeholder-drop.spec.js:71:45

_{48923db Run}

[tellthemachines]

@sirreal I assume the draft status is because it hasn't been human reviewed yet; are you planning to do so? Happy to give it a review and test run once it's marked ready.

[sirreal]

@tellthemachines Yep, this was waiting on my self-review and some numbers. I did some testing and here are the results.

In summary, This seems to outperform trunk. Keeping the accessor cache adds a very small improvement that doesn't seem worth it.

I'll perform self-review and mark as ready, then I'd love feedback or land if/when you're happy with it.

Full LLM-driven perf measurements

Method. Base 4791f174f20, WP_DEBUG off (it bypasses the accessor cache), get_merged_data() wrapped with a timer and call counter. Table 1: curl, 21 requests per page, first dropped, median, WordPress trunk. Table 2: npm run perf, 3 rounds of 16 samples, WordPress 7.1.3. Compare columns within a table only.

Time in full merges per request.

Page	trunk: merges	trunk	this PR	PR + accessor cache
twentytwentythree front page	7	3.59 ms	2.03 ms	1.97 ms
twentytwentyfour front page	24	6.61 ms	1.92 ms	1.88 ms
single post, large-post.html fixture	8	3.64 ms	1.96 ms	1.85 ms
post with 52 blocks carrying an is-style-* class	58	12.92 ms	1.92 ms	1.90 ms

About 1.9 ms is the first merge per origin and remains in every column.

Callers that still merge on trunk. The accessor cache serves only gutenberg_get_global_styles(). The rest: gutenberg_render_block_style_variation_support_styles() once per is-style-* block (1, 18, 2 and 52 above); gutenberg_get_global_stylesheet() twice; gutenberg_add_global_styles_for_blocks(), WP_Duotone_Gutenberg::get_all_global_style_block_names(), gutenberg_get_global_settings() and the first layout call once each.

REST posts?context=edit. Content is rendered three times per post, so each is-style-* block costs three merges on trunk. Three posts listed, one the 52-block post:

	merges	merge time	wpTotal
trunk	159	31.7 ms	148 ms
this PR	471 (memoized)	2.3 ms	119 ms
PR + accessor cache	159	2.1 ms	119 ms

The editor perf suites miss this: their fixtures have no is-style-* blocks. A blog index listing that post behaves the same (56 merges, 11.9 ms on trunk, 2.0 ms here).

Trunk with #81889 reverted measures the same as trunk on every page: equal merge counts, merge time within 0.2 ms. The layout static served the same calls the accessor cache does.

Request level.

Suite	Metric	trunk	this PR	PR + accessor cache
front-end-block-theme	wpTemplate	15.73 ms	13.49 ms	13.62 ms
front-end-block-theme	wpTotal	54.45 ms	52.31 ms	53.17 ms
front-end-classic-theme	wpTemplate	12.04 ms	10.86 ms	10.79 ms
front-end-classic-theme	wpTotal	50.53 ms	49.62 ms	50.22 ms

Round spread is at most 0.6 ms on wpTemplate and 1.9 ms on wpTotal; the classic-suite wpTotal difference is inside it.

Accessor cache on top of the memo: no measurable difference. A hit saves one memoized call, 0.34 µs.

Memory. wpMemoryUsage fell 81 KB (block) and 69 KB (classic). Not investigated.

Not measured. global-styles/<id>, templates and template-parts make no plugin resolver calls; global-styles/themes/<stylesheet> makes one. The editor's single-post load, posts/<id>?context=edit, was not run on its own. Scripts and raw results on request.

[tellthemachines]

Thanks for the PR! The code LGTM and I couldn't find any issues in manual testing. I'm not an expert in this area though, so feel free to get a second opinion 😄

Looking at the perf numbers it makes a lot of sense to replace #81889 with this.

Just curious, any reason the tests in the first table were run on TT3 and TT4 but not TT5?

[sirreal]

any reason the tests in the first table were run on TT3 and TT4 but not TT5?

No conscious decision on my part to do that. I'm happy to run more numbers if we'd like.

[tellthemachines]

I'm happy to run more numbers if we'd like.

I don't think it's necessary, TT4 has a ton of blocks on its front page so if it works there it should be good for the other themes 😄

[sirreal]

I'm not an expert in this area

Me neither unfortunately 😅

I'll leave this open for another day or so in case other folks can have a look.