Sandbox::https://github.com/withastro/astro/pull/17857

Princesseuh · 2026-08-29T17:04:49Z

Changes

This PR improves the overall performance of our rendering pipeline, without changing the entire structure or anything, just mostly focused on reducing allocations, preventing V8 de-opt, and/or just faster code in some places.

This of course mostly improves SSR performance, but nonetheless, in local this makes the docs build 2s faster on my computer. In SSR stress benchmarks, this has resulted in a up to 70% improvement in raw ops/s, but it's of course not representing real work.

Testing

Tests should pass. Also added some tests for behavior that I found easy to regress by accident while working on this.

Docs

N/A

changeset-bot · 2026-08-29T17:04:55Z

🦋 Changeset detected

Latest commit: 8514d2b

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

codspeed · 2026-08-29T17:11:26Z

Merging this PR will improve performance by 30.93%

⚠️

Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 9 improved benchmarks
✅ 12 untouched benchmarks

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	`large-array (BufferedRenderer per child)`	194.9 ms	121 ms	+61.05%
⚡	`many-slots (eager slot prerendering)`	6.5 ms	4.4 ms	+49.51%
⚡	`large-array [streaming]`	164.4 ms	112.7 ms	+45.88%
⚡	`many-components [streaming]`	8.2 ms	5.7 ms	+43.54%
⚡	`many-components (markHTMLString, isHTMLString, validateProps)`	9.6 ms	7.5 ms	+28.15%
⚡	`Rendering: streaming [true], .astro file`	208.8 ms	165.7 ms	+25.98%
⚡	`many-expressions [streaming]`	13.7 ms	12.2 ms	+12.28%
⚡	`Rendering: streaming [false], .astro file`	198.8 ms	177.7 ms	+11.89%
⚡	`many-expressions (renderChild dispatch, escapeHTML)`	14.8 ms	13.4 ms	+10.58%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing perf/server-render-allocations (8514d2b) with main (2fc7ce9)¹}

No successful run was found on main (de5cc2d) during the generation of this report, so 2fc7ce9 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

Princesseuh · 2026-09-07T12:28:44Z

@@ -1,8 +1,35 @@
-import { escape } from 'html-escaper';


I know, I know, this is scary, however the code here is incredibly hot (🔥 🔥), and as such it needs a very fast HTML escape solution. This code is between 2 to 3 times as fast depending on the workload and is really similar (albeit slightly tuned to Astro's use case) to rising stars libraries like https://github.com/SukkaW/fast-escape-html

In a further PR, I'd like to perhaps remove that dep completely and have our own escape.ts somewhere that we re-use.

I am not worried about "being scary", but maybe this change should be part of its own PR:

if we break something, we can revert only this change

this PR doesn't have a test suite to cover the dep we're removing (we assume it's tested)

ematipico

The changes make sense. I suggested to move the HTML escape into its own PR. Let's wait for when Matthew comes back, I would like his review too

ematipico · 2026-09-07T13:56:15Z

@@ -1,8 +1,35 @@
-import { escape } from 'html-escaper';


I am not worried about "being scary", but maybe this change should be part of its own PR:

if we break something, we can revert only this change

this PR doesn't have a test suite to cover the dep we're removing (we assume it's tested)

astro-factory

No findings.

Merge Requirement Assessment

Status: satisfied

Improve SSR rendering performance by reducing allocations, avoiding V8 deopts, and using faster rendering paths — implemented across packages/astro/src/runtime/server/ (escape, render-child dispatch, template-result rendering, streaming engine, attribute spreading, slot handling, fetch-state slots) and covered by dedicated regression tests for frozen Astro globals, frozen render instructions, hydration attribute escaping, thenable-versus-render-instance precedence, and sync subtree expansion.

Questions

None.

Review Status

Verdict: ready to merge based on static review
Context: PR #17857 (#17857)
Scope: full PR diff (22 files) at head 70824a3c928e4421190d71d4d79d00fe423ab41d against base 92f23cc121d3a1a03c6fb901a519309662b333de
Changeset: present and covers astro
Limitations: none
Validation: Static review only; no project code, tests, builds, or checks were run.
GitHub context: collected
Git scope: PR base/head verified via read-only GitHub tools; 0 unresolved prior review threads.

This review was made by an LLM. The analysis may be wrong, and reports might be incorrect.

Princesseuh · 2026-09-07T14:00:08Z

@ematipico We have several tests for HTML escaping, https://github.com/withastro/astro/blob/9870f95601690d9d98799b6fa78a0bc76165ee06/packages/astro/test/html-escape.test.ts https://github.com/withastro/astro/blob/9870f95601690d9d98799b6fa78a0bc76165ee06/packages/astro/test/units/render/escape.test.ts

and a few more elsewhere. The code there has already changed through times between a custom version vs the dep vs other stuff

ematipico · 2026-09-07T14:01:56Z

LOL the package has like 4 tests 🤣

matthewp · 2026-09-08T12:51:22Z

 	return markHTMLString(content);
 }

+const HEAD_INSTRUCTION = Object.freeze(


bonus points for using Object.freeze

…oComponent

…ng engine

…d styles

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [astro](https://astro.build) ([source](https://github.com/withastro/astro/tree/HEAD/packages/astro)) | [`7.3.2` → `7.3.3`](https://renovatebot.com/diffs/npm/astro/7.3.2/7.3.3) | ![age](https://developer.mend.io/api/mc/badges/age/npm/astro/7.3.3?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/astro/7.3.2/7.3.3?slim=true) | --- ### Release Notes <details> <summary>withastro/astro (astro)</summary> ### [`v7.3.3`](https://github.com/withastro/astro/blob/HEAD/packages/astro/CHANGELOG.md#733) [Compare Source](https://github.com/withastro/astro/compare/astro@7.3.2...astro@7.3.3) ##### Patch Changes - [#17651](withastro/astro#17651) [`504333c`](withastro/astro@504333c) Thanks [@sxzz](https://github.com/sxzz)! - Refactors internal version handling to use a smaller, ESM-native dependency - [#17942](withastro/astro#17942) [`0bc5715`](withastro/astro@0bc5715) Thanks [@matthewp](https://github.com/matthewp)! - Returns appropriate 400 and 404 responses from the image endpoint for invalid and missing local image paths - [#17700](withastro/astro#17700) [`b2222fc`](withastro/astro@b2222fc) Thanks [@winklemad](https://github.com/winklemad)! - Fixes `Astro.preferredLocaleList` returning an empty list when a locale is configured with the object form (`{ path, codes }`) and the browser sends the code with different casing or an underscore, such as `en-US` matching a configured `en-us` - [#17941](withastro/astro#17941) [`394ff79`](withastro/astro@394ff79) Thanks [@matthewp](https://github.com/matthewp)! - Fixes `astro preview --ignore-lock` (and `astro dev --ignore-lock`) being refused when run from an AI agent environment. The flag now starts the server in the foreground instead of erroring, since agent detection only inferred background mode and was never explicitly requested. An explicit `--background` combined with `--ignore-lock` still errors. - [#17928](withastro/astro#17928) [`3277927`](withastro/astro@3277927) Thanks [@ArmandPhilippot](https://github.com/ArmandPhilippot)! - Fixes TypeScript autocompletion for `getImage()` to suggest all available predefined options. - [#17928](withastro/astro#17928) [`3277927`](withastro/astro@3277927) Thanks [@ArmandPhilippot](https://github.com/ArmandPhilippot)! - Fixes a type error in `getImage()` options that allowed passing both `widths` and `densities` at the same time. - [#17857](withastro/astro#17857) [`2637ed1`](withastro/astro@2637ed1) Thanks [@Princesseuh](https://github.com/Princesseuh)! - Improves rendering performance - [#17943](withastro/astro#17943) [`2fc7ce9`](withastro/astro@2fc7ce9) Thanks [@matthewp](https://github.com/matthewp)! - Fixes a WebAssembly error when importing `astro:actions` in tests that run under `@cloudflare/vitest-pool-workers` - [#18018](withastro/astro#18018) [`1b5a234`](withastro/astro@1b5a234) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes trailing-slash redirect response body pointing to the incoming URL instead of the redirect target. The `location` header was correct, but the HTML body (`<meta http-equiv="refresh">`, `<title>`, and `<a>` tag) contained the original request path without the trailing-slash correction or query string. - [#17905](withastro/astro#17905) [`eaf70fa`](withastro/astro@eaf70fa) Thanks [@SudoDevStudio](https://github.com/SudoDevStudio)! - Fixes custom dev toolbar apps losing their UI after client-side navigation with `<ClientRouter />`. - [#18011](withastro/astro#18011) [`558b301`](withastro/astro@558b301) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes prerendered Cloudflare pages rendering as `[object Object]` when `nodejs_compat` is enabled in `wrangler.toml` - [#17944](withastro/astro#17944) [`ba08e35`](withastro/astro@ba08e35) Thanks [@matthewp](https://github.com/matthewp)! - Fixes a regression in `astro dev` where writes outside the module graph (for example, `@astrojs/cloudflare`'s `.wrangler/state` files) invalidated the middleware on every request, causing repeated SSR reloads. Such writes no longer invalidate the middleware. - [#17531](withastro/astro#17531) [`ae837db`](withastro/astro@ae837db) Thanks [@danilloestrela](https://github.com/danilloestrela)! - Updates `svgo` to `4.0.2` to resolve a security advisory - [#17953](withastro/astro#17953) [`dbbf10e`](withastro/astro@dbbf10e) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes a one-time page reload shortly after the first load on cold dev-server starts when a project has framework components imported from MDX content entries. MDX files are now included in the dev dependency pre-bundling scan, so their framework dependencies are bundled up front instead of being discovered (and reloaded for) at runtime. - [#17955](withastro/astro#17955) [`4e8ad9a`](withastro/astro@4e8ad9a) Thanks [@matthewp](https://github.com/matthewp)! - Improves dev server startup time. The content config and dev server app module graphs now begin compiling during server creation without blocking the server from listening. Request handling waits for the shared setup result when needed, cutting `astro dev` ready time by roughly a third on projects with a content config. - [#17960](withastro/astro#17960) [`9838049`](withastro/astro@9838049) Thanks [@Chy-Zaber-Bin-Zahid](https://github.com/Chy-Zaber-Bin-Zahid)! - Improves the diagnostics of some Astro errors. - [#17998](withastro/astro#17998) [`0e5478d`](withastro/astro@0e5478d) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes SVG `<style>` elements nested inside `<defs>` or other container elements not being hashed for CSP - [#17994](withastro/astro#17994) [`80f9f1d`](withastro/astro@80f9f1d) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes `experimental.incrementalBuild` restoring pages with stale CSS after a preprocessor partial changes or missing original images referenced by restored pages - [#17889](withastro/astro#17889) [`8ae6b46`](withastro/astro@8ae6b46) Thanks [@ajfAfg](https://github.com/ajfAfg)! - Fixes a bug where the dev server stripped the configured `base` from URLs that only share a prefix with it. With `base: '/s'`, requests to `/src/...` were rewritten to `/rc/...` and failed, breaking those pages during development. - [#17980](withastro/astro#17980) [`cfccafa`](withastro/astro@cfccafa) Thanks [@gameroman](https://github.com/gameroman)! - Improves JSDoc for fonts api - [#17953](withastro/astro#17953) [`dbbf10e`](withastro/astro@dbbf10e) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes CSS HMR for framework components rendered through content entries after `ClientRouter` navigation - [#17970](withastro/astro#17970) [`0b4dc3a`](withastro/astro@0b4dc3a) Thanks [@matthewp](https://github.com/matthewp)! - Improves serialization of transition animation values in generated CSS - [#17999](withastro/astro#17999) [`30ef3cb`](withastro/astro@30ef3cb) Thanks [@astro-factory](https://github.com/apps/astro-factory)! - Fixes content collection HMR not updating prerendered pages when an adapter enables a separate prerender environment (e.g. `@astrojs/cloudflare` with `prerenderEnvironment: 'node'`) - [#18002](withastro/astro#18002) [`312ab49`](withastro/astro@312ab49) Thanks [@shoutoutuoadi325](https://github.com/shoutoutuoadi325)! - Fixes redirect targets being corrupted when a dynamic route parameter value contains `$` replacement patterns like `$&` - [#17937](withastro/astro#17937) [`e294953`](withastro/astro@e294953) Thanks [@matthewp](https://github.com/matthewp)! - Fixes a bug where the `glob()` content loader kept stale entries in the data store after the last file in a collection was deleted. Empty collections are now pruned correctly, and the file watcher is registered in dev so the first file added to an empty collection is picked up without a restart. - [#17945](withastro/astro#17945) [`750b4db`](withastro/astro@750b4db) Thanks [@matthewp](https://github.com/matthewp)! - Pre-bundles renderer server entrypoints and the default console logger during dev so they are included in the initial optimization pass, preventing a mid-request re-optimization that could crash the dev server on Cloudflare (workerd). </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).

github-actions Bot added the pkg: astro Related to the core `astro` package (scope) label Aug 29, 2026

Princesseuh force-pushed the perf/server-render-allocations branch 6 times, most recently from 400137f to e609ba6 Compare September 3, 2026 17:30

Princesseuh commented Sep 7, 2026

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Princesseuh marked this pull request as ready for review September 7, 2026 13:10

Princesseuh changed the title ~~perf(runtime): reduce server-side render allocations~~ perf(runtime): improve rendering performance Sep 7, 2026

ematipico added the pr: astro-review Triggers a bot to do an automated review label Sep 7, 2026

astro-factory Bot removed the pr: astro-review Triggers a bot to do an automated review label Sep 7, 2026

ematipico reviewed Sep 7, 2026

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astro-factory Bot reviewed Sep 7, 2026

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matthewp reviewed Sep 8, 2026

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Comment thread packages/astro/src/core/fetch/fetch-state.ts Resolved

matthewp reviewed Sep 8, 2026

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Princesseuh added 10 commits September 9, 2026 16:24

perf(runtime): reduce server-side render allocations

d6ac9cb

perf(runtime): return the component instance directly from renderAstr…

a582d91

…oComponent

perf(runtime): expand sync component and slot subtrees in the streami…

1f00ef4

…ng engine

perf(runtime): escape HTML with a scan loop instead of a regex callback

e9a12e7

perf(runtime): avoid intermediate arrays when spreading attributes an…

caba2ac

…d styles

perf(runtime): cache attribute-name classification in addAttribute

b967c4b

perf(runtime): avoid the entries array in spreadAttributes

16c740b

perf(runtime): give the streaming engine stable helper identities

c80520a

perf(runtime): share the Astro.slots accessor across component renders

2af0b37

perf(runtime): reuse stateless render instructions

d6dd1bb

Princesseuh added 16 commits September 9, 2026 16:32

perf(runtime): drop the in-operator probe from isRenderInstance

7f61a85

perf(runtime): extract directives without materializing prop entries

2c98f41

perf(runtime): strip static slots only from renderer output

6d0679b

chore: add changeset for render improvements

d758231

chore(runtime): fix prefer-for-of and prefer-includes lint errors

c84b821

fix(runtime): match buffered-path semantics when expanding sync subtrees

a1ffad0

fix(runtime): preserve optimized rendering semantics

f4bc28a

refactor(runtime): type shared slot state

60a1a0d

refactor(runtime): prune redundant comments

30c5de8

refactor(runtime): clarify streaming state names

8ef51e6

docs(runtime): restore rendering comments

081366d

perf(runtime): remove HTML escape fallback

af61a47

refactor(runtime): narrow render type assertions

1c1a6e0

fix(runtime): coerce renderer attributes before escaping

4e3b153

refactor(runtime): clarify rendering constants

e518435

chore: move to ssrresult

dc81a5a

Princesseuh force-pushed the perf/server-render-allocations branch from ab3f880 to dc81a5a Compare September 9, 2026 14:41

github-actions Bot added the docs pr label Sep 9, 2026

matthewp reviewed Sep 9, 2026

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Comment thread packages/astro/src/core/fetch/fetch-state.ts Resolved

matthewp reviewed Sep 9, 2026

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Comment thread packages/astro/src/runtime/server/render/util.ts Resolved

refactor(runtime): refine internal rendering state

92395ce

matthewp approved these changes Sep 9, 2026

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Update fresh-otters-run.md

8514d2b

Princesseuh merged commit 2637ed1 into main Sep 9, 2026
29 checks passed

Princesseuh deleted the perf/server-render-allocations branch September 9, 2026 16:11

astrobot-houston mentioned this pull request Sep 9, 2026

[ci] release #17939

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tommyp mentioned this pull request Oct 12, 2026

chore(deps): update astro, vitest, prettier-plugin-astro, svelte, and 8 others tommyp/tommyp.org#23

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spectator81-png mentioned this pull request Oct 21, 2026

CSP: hashes from Astro.csp.insertScriptHash() in components inside <body> are dropped (regression in 7.3.3 for layouts with a named slot in <head>) #18479

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jp-knj mentioned this pull request Oct 25, 2026

fix(csp): include hashes inserted by body components in the CSP meta tag for non-streaming renders #18512

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Merging this PR will improve performance by 30.93%

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