Handle ssr.external: true for isDepExternaled (#19)

Author: bluwy

Diff for: src/sync.cjs

@@ -24,7 +24,16 @@ function isDepNoExternaled(dep, ssrNoExternal) {
 
 /** @type {import('./index.d.ts').isDepExternaled} */
 function isDepExternaled(dep, ssrExternal) {
-  return ssrExternal.includes(dep)
+  // If `ssrExternal` is `true`, it just means that all linked
+  // dependencies should also be externalized by default. It doesn't
+  // mean that a dependency is being explicitly externalized. So we
+  // return `false` in this case.
+  // @ts-expect-error can be true in Vite 6
+  if (ssrExternal === true) {
+    return false
+  } else {
+    return ssrExternal.includes(dep)
+  }
 }
 
 /**