fix(vitest): resolve each inline project's own config under Vitest 5

.changeset/vitest-5-shared-server-projects.md

@@ -0,0 +1,5 @@
+---
+'@solidjs/vite-plugin': patch
+---
+
+When the root config declares `test.projects` and leaves `test.sharedViteServer` unset, the plugin now sets it to `false` so every inline project resolves its own Vite config, as under Vitest 4; an explicit value is respected. Vitest 5 defaults the option to `true`, and a shared inline project takes its `test` options from the raw root block captured before any `config` hook runs, so it lost everything the plugin injects (posture, the `@testing-library/jest-dom` setup file, `server.deps`). Refs #369.

README.md

@@ -1045,6 +1045,8 @@ test: {
 },
 ```
 
+The posture is chosen while each project resolves its own Vite config. Vitest 5 lets inline projects reuse the root Vite server instead (`test.sharedViteServer`, on by default), which skips that step, so the plugin sets `sharedViteServer: false` when the root config declares `test.projects` — trading Vitest 5's shared-server optimization for the per-project resolution Vitest 4 always did. Setting the option yourself overrides this; with `true`, every shared project runs with the root config's posture, without the injected `jest-dom` setup file, and without the plugin's `server.deps` handling (the framework inlined for the server posture, externalized for the client one).
+
 # Credits
 
 - [solid-js](https://github.com/solidjs/solid)

examples/start-ssr/test/run.mjs

@@ -5231,6 +5231,53 @@ async function runVitestMode() {
     projectsEnvPass ? undefined : projectsEnvError || `environment: ${projectsEnv}`,
   );
 
+  // Vitest 5 defaults `test.sharedViteServer` to true, and a shared inline
+  // project takes its `test` options from the raw root block captured before
+  // any `config` hook runs — so it would never see the posture, jest-dom
+  // setup file, or server.deps the plugin injects (#369). The plugin turns
+  // sharing off when the root declares `test.projects` and the user hasn't
+  // chosen. Asserted at the config-resolution level, which is
+  // version-independent: the examples pin vitest 4, where the option has no
+  // effect, but the resolved value is what Vitest 5's getOwnServerReason
+  // reads.
+  const resolveSharedViteServer = async (testBlock) => {
+    const resolved = await resolveConfig(
+      { root: exampleDir, mode: 'test', test: testBlock },
+      'serve',
+    );
+    return resolved.test?.sharedViteServer;
+  };
+  const projectsBlock = [{ extends: true, test: { name: 'node', environment: 'node' } }];
+  let sharedWithProjects;
+  let sharedWithoutProjects;
+  let sharedExplicit;
+  let sharedError = '';
+  try {
+    sharedWithProjects = await resolveSharedViteServer({ projects: projectsBlock });
+    sharedWithoutProjects = await resolveSharedViteServer({});
+    sharedExplicit = await resolveSharedViteServer({
+      projects: projectsBlock,
+      sharedViteServer: true,
+    });
+  } catch (e) {
+    sharedError = String(e);
+  }
+  const sharedPass =
+    !sharedError &&
+    sharedWithProjects === false &&
+    sharedWithoutProjects === undefined &&
+    sharedExplicit === true;
+  record(
+    mode,
+    'shared-vite-server',
+    'root config with test.projects gets sharedViteServer: false (untouched without projects, explicit true preserved)',
+    sharedPass,
+    sharedPass
+      ? undefined
+      : sharedError ||
+          `projects: ${sharedWithProjects}, none: ${sharedWithoutProjects}, explicit: ${sharedExplicit}`,
+  );
+
   // The jest-dom setup file is injected only when the PROJECT can resolve
   // `@testing-library/jest-dom` — by walking node_modules up from the Vite
   // root, the way vitest itself resolves bare `setupFiles`. Two ways the

src/index.ts

@@ -1192,6 +1192,16 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
           test.environment = 'jsdom';
         }
 
+        // Vitest 5 defaults `test.sharedViteServer` to true: inline projects
+        // then reuse the root Vite server and take their `test` options from
+        // the raw root block captured BEFORE any `config` hook runs, so nothing
+        // injected here (posture, jest-dom, server.deps) reaches them. Vitest
+        // reads the option off the resolved root config (getOwnServerReason), so
+        // this restores per-project resolution as under Vitest 4 (#369).
+        if (userTest.projects && userTest.sharedViteServer === undefined) {
+          test.sharedViteServer = false;
+        }
+
         if (serverTestPosture) {
           // The worker pool is shared across the whole vitest workspace and
           // imports externalized deps natively with `--conditions` derived