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fix: avoid client modules while traversing dependencies to prevent FOUC during dev #14577

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Merged
merged 3 commits into from
Oct 3, 2025
+28 −10
Merged

fix: avoid client modules while traversing dependencies to prevent FOUC during dev #14577

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070d4f3
fix: avoid client modules while traversing dependencies to prevent FO…
dummdidumm Oct 2, 2025
0ed8037
Merge branch 'main' into load-module-ssr-fix
Rich-Harris Oct 3, 2025
cd4174a
snake_case
Rich-Harris Oct 3, 2025
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5 changes: 5 additions & 0 deletions .changeset/late-banks-clean.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@sveltejs/kit': patch
---

fix: avoid client modules while traversing dependencies to prevent FOUC during dev
33 changes: 23 additions & 10 deletions packages/kit/src/exports/vite/dev/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -234,7 +234,7 @@ export async function dev(vite, vite_config, svelte_config, get_remotes) {
// in dev we inline all styles to avoid FOUC. this gets populated lazily so that
// components/stylesheets loaded via import() during `load` are included
result.inline_styles = async () => {
/** @type {Set<import('vite').ModuleNode>} */
/** @type {Set<import('vite').ModuleNode | import('vite').EnvironmentModuleNode>} */
const deps = new Set();

for (const module_node of module_nodes) {
Expand Down Expand Up @@ -610,16 +610,16 @@ function remove_static_middlewares(server) {

/**
* @param {import('vite').ViteDevServer} vite
* @param {import('vite').ModuleNode} node
* @param {Set<import('vite').ModuleNode>} deps
* @param {import('vite').ModuleNode | import('vite').EnvironmentModuleNode} node
* @param {Set<import('vite').ModuleNode | import('vite').EnvironmentModuleNode>} deps
*/
async function find_deps(vite, node, deps) {
// since `ssrTransformResult.deps` contains URLs instead of `ModuleNode`s, this process is asynchronous.
// instead of using `await`, we resolve all branches in parallel.
/** @type {Promise<void>[]} */
const branches = [];

/** @param {import('vite').ModuleNode} node */
/** @param {import('vite').ModuleNode | import('vite').EnvironmentModuleNode} node */
async function add(node) {
if (!deps.has(node)) {
deps.add(node);
Expand All @@ -629,20 +629,23 @@ async function find_deps(vite, node, deps) {

/** @param {string} url */
async function add_by_url(url) {
const node = await vite.moduleGraph.getModuleByUrl(url);
const node = await get_server_module_by_url(vite, url);

if (node) {
await add(node);
}
}

if (node.ssrTransformResult) {
if (node.ssrTransformResult.deps) {
node.ssrTransformResult.deps.forEach((url) => branches.push(add_by_url(url)));
const transform_result =
/** @type {import('vite').ModuleNode} */ (node).ssrTransformResult || node.transformResult;

if (transform_result) {
if (transform_result.deps) {
transform_result.deps.forEach((url) => branches.push(add_by_url(url)));
}

if (node.ssrTransformResult.dynamicDeps) {
node.ssrTransformResult.dynamicDeps.forEach((url) => branches.push(add_by_url(url)));
if (transform_result.dynamicDeps) {
transform_result.dynamicDeps.forEach((url) => branches.push(add_by_url(url)));
}
} else {
node.importedModules.forEach((node) => branches.push(add(node)));
Expand All @@ -651,6 +654,16 @@ async function find_deps(vite, node, deps) {
await Promise.all(branches);
}

/**
* @param {import('vite').ViteDevServer} vite
* @param {string} url
*/
function get_server_module_by_url(vite, url) {
return vite.environments
? vite.environments.ssr.moduleGraph.getModuleByUrl(url)
: vite.moduleGraph.getModuleByUrl(url, true);
}

/**
* Determine if a file is being requested with the correct case,
* to ensure consistent behaviour between dev and prod and across
Expand Down
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