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fix: prepend the server-component bootstrap to the hydration script #294

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fix: prepend the server-component bootstrap to the hydration script #294

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5 changes: 5 additions & 0 deletions .changeset/clean-server-component-hydration.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'vite-plugin-solid': patch
---

Prevent generated server-component hydration from shifting the `<head>` structure. The bootstrap now runs at the start of the existing hydration script instead of adding an unexpected first child to `<head>`.
19 changes: 11 additions & 8 deletions examples/turnkey/test/run.mjs
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Expand Up @@ -1433,19 +1433,22 @@ async function runFramesChecks(mode, origin) {
html.split(`${FRAMES_SECRET}-one`).length === 2,
);
record(mode, 'document', 't=0 slot records shipped (sc:slot)', html.includes('sc:slot:'));
// Presence is not enough: the render plugin serializes a placeholder as
// `self._$SC.r(id)`, so the registry must be defined BEFORE the hydration
// data script runs. Anchoring the injection on `</head>` put it after
// <HydrationScript />, and any document whose payload carried a frame ref
// threw "Cannot read properties of undefined (reading 'r')" — killing
// hydration, so nothing in the page was interactive.
// Presence is not enough: the bootstrap must run before hydration data,
// but adding a separate script before the document's declared head nodes
// shifts Solid's structural hydration cursor. It belongs at the front of
// the existing HydrationScript instead.
const scBootstrapAt = html.indexOf('self._$SC=');
const hydrationRuntimeAt = html.indexOf('window._$HY');
const hydrationDataAt = html.indexOf('_$HY.r[');
record(
mode,
'document',
'SC bootstrap inline in head, before the hydration data script',
scBootstrapAt !== -1 && (hydrationDataAt === -1 || scBootstrapAt < hydrationDataAt),
'SC bootstrap starts the hydration script before hydration data',
scBootstrapAt !== -1 &&
hydrationRuntimeAt > scBootstrapAt &&
html.lastIndexOf('<script', scBootstrapAt) ===
html.lastIndexOf('<script', hydrationRuntimeAt) &&
(hydrationDataAt === -1 || scBootstrapAt < hydrationDataAt),
);

const chrome = startProcess(CHROME, [
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17 changes: 8 additions & 9 deletions src/ssr/index.ts
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Expand Up @@ -354,9 +354,9 @@ export function ssrServe(
const composeServerFunctions = (isBuild || externalDev) && internal.serverFunctions;
// Generated entries own the whole document wiring, so the handler also
// injects the server-component bootstrap (the per-function-id
// placeholder registry the render plugin references; must be inline at
// the TOP of <head>, before the hydration data script streams in — see
// the transform below). Authored entries inject it themselves.
// placeholder registry the render plugin references; must start the
// hydration runtime script, before hydration data streams in — see the
// transform below). Authored entries inject it themselves.
const injectComponentBootstrap = generated && serverComponents;

const lines = [
Expand Down Expand Up @@ -419,17 +419,16 @@ export function ssrServe(
// placeholder as `self._$SC.r(id)`, so a document whose payload carries
// one throws on that reference if the registry is not defined yet.
// <HydrationScript /> sits inside <head>, so anchoring on `</head>`
// always lands after it — the opening tag is the only anchor that is
// reliably before it.
// always lands after it. Prepend the bootstrap to that existing script
// so it runs first without adding a node that shifts hydration.
lines.push(
` if (!bootstrapped) {`,
` const headOpen = /<head(\\s[^>]*)?>/.exec(chunk);`,
` if (headOpen) {`,
` const at = chunk.indexOf('window._$HY');`,
` if (at !== -1) {`,
` bootstrapped = true;`,
` const at = headOpen.index + headOpen[0].length;`,
` chunk =`,
` chunk.slice(0, at) +`,
` '<script>' + SERVER_COMPONENT_BOOTSTRAP + '</' + 'script>' +`,
` SERVER_COMPONENT_BOOTSTRAP +`,
` chunk.slice(at);`,
` }`,
` }`,
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