fix(start-plugin): invoke server implementation of createIsomorphicFn during SSR (#3268)

Author: djgrant

e2e/start/basic/app/routes/isomorphic-fns.tsx

@@ -5,31 +5,39 @@ import { useState } from 'react'
 const getEnv = createIsomorphicFn()
   .server(() => 'server')
   .client(() => 'client')
+
 const getServerEnv = createServerFn().handler(() => getEnv())
 
 const getEcho = createIsomorphicFn()
   .server((input: string) => 'server received ' + input)
   .client((input) => 'client received ' + input)
+
 const getServerEcho = createServerFn()
   .validator((input: string) => input)
   .handler(({ data }) => getEcho(data))
 
 export const Route = createFileRoute('/isomorphic-fns')({
   component: RouteComponent,
+  loader() {
+    return {
+      envOnLoad: getEnv(),
+    }
+  },
 })
 
 function RouteComponent() {
+  const { envOnLoad } = Route.useLoaderData()
   const [results, setResults] = useState<Partial<Record<string, string>>>()
   async function handleClick() {
-    const env = getEnv()
+    const envOnClick = getEnv()
     const echo = getEcho('hello')
     const [serverEnv, serverEcho] = await Promise.all([
       getServerEnv(),
       getServerEcho({ data: 'hello' }),
     ])
-    setResults({ env, echo, serverEnv, serverEcho })
+    setResults({ envOnClick, echo, serverEnv, serverEcho })
   }
-  const { env, echo, serverEnv, serverEcho } = results || {}
+  const { envOnClick, echo, serverEnv, serverEcho } = results || {}
   return (
     <div>
       <button onClick={handleClick} data-testid="test-isomorphic-results-btn">
@@ -43,7 +51,9 @@ function RouteComponent() {
           When we called the function on the server it returned:
           <pre data-testid="server-result">{JSON.stringify(serverEnv)}</pre>
           When we called the function on the client it returned:
-          <pre data-testid="client-result">{JSON.stringify(env)}</pre>
+          <pre data-testid="client-result">{JSON.stringify(envOnClick)}</pre>
+          When we called the function during SSR it returned:
+          <pre data-testid="ssr-result">{JSON.stringify(envOnLoad)}</pre>
           <br />
           <h1>
             <code>echo</code>

e2e/start/basic/tests/server-functions.spec.ts

@@ -95,6 +95,7 @@ test('isomorphic functions can have different implementations on client and serv
 
   await expect(page.getByTestId('server-result')).toContainText('server')
   await expect(page.getByTestId('client-result')).toContainText('client')
+  await expect(page.getByTestId('ssr-result')).toContainText('server')
 
   await expect(page.getByTestId('server-echo-result')).toContainText(
     'server received hello',

packages/start-plugin/src/compilers.ts

@@ -529,7 +529,7 @@ function handleCreateIsomorphicFnCallExpression(
     )
   }
 
-  const resolvedEnv = opts.env === 'ssr' ? 'client' : opts.env
+  const resolvedEnv = opts.env === 'ssr' ? 'server' : opts.env
 
   const envCallExpression = callExpressionPaths[resolvedEnv]