From c8862e3c93d9b444b0cf9f16770284e47470947f Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 15:13:28 +0200
Subject: [PATCH 01/10] Try to run test

---
 .github/workflows/build_and_test.yml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/build_and_test.yml b/.github/workflows/build_and_test.yml
index ab1ce6a55b37f..7b172febda96d 100644
--- a/.github/workflows/build_and_test.yml
+++ b/.github/workflows/build_and_test.yml
@@ -705,10 +705,11 @@ jobs:
       afterBuild: |
         export NEXT_TEST_MODE=start
 
-        node run-tests.js \
+        node run-tests.js --type production \
           test/e2e/app-dir/app/index.test.ts \
           test/e2e/app-dir/app-edge/app-edge.test.ts \
-          test/e2e/app-dir/metadata-edge/index.test.ts
+          test/e2e/app-dir/metadata-edge/index.test.ts \
+          test/e2e/app-dir/non-root-project-monorepo/non-root-project-monorepo.test.ts
       stepName: 'test-prod-windows'
       runs_on_labels: '["windows","self-hosted","x64"]'
       buildNativeTarget: 'x86_64-pc-windows-msvc'

From 54013dc3e87f0d34d5ca88aac089d42500a2ba48 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 15:13:34 +0200
Subject: [PATCH 02/10] Fix

---
 crates/napi/src/next_api/project.rs           |  7 ++-
 crates/next-api/src/project.rs                | 46 +++++++++----------
 packages/next/src/build/swc/types.ts          |  9 ++--
 .../next/src/build/turbopack-build/impl.ts    |  4 +-
 .../webpack/loaders/css-loader/src/utils.ts   |  5 +-
 packages/next/src/lib/normalize-path.ts       |  5 ++
 .../src/server/dev/hot-reloader-turbopack.ts  | 13 +++---
 7 files changed, 47 insertions(+), 42 deletions(-)
 create mode 100644 packages/next/src/lib/normalize-path.ts

diff --git a/crates/napi/src/next_api/project.rs b/crates/napi/src/next_api/project.rs
index 2d045a831d017..b36fe0c02042a 100644
--- a/crates/napi/src/next_api/project.rs
+++ b/crates/napi/src/next_api/project.rs
@@ -392,7 +392,9 @@ pub fn project_new(
 
             let subscriber = subscriber.with(FilterLayer::try_new(&trace).unwrap());
 
-            let internal_dir = PathBuf::from(&options.project_path).join(&options.dist_dir);
+            let internal_dir = PathBuf::from(&options.root_path)
+                .join(&options.project_path)
+                .join(&options.dist_dir);
             std::fs::create_dir_all(&internal_dir)
                 .context("Unable to create .next directory")
                 .unwrap();
@@ -1426,7 +1428,8 @@ pub async fn get_source_map_rope(
 
     let Some(chunk_base) = file.strip_prefix(
         &(format!(
-            "{}/{}/",
+            "{}/{}/{}",
+            container.project().await?.root_path,
             container.project().await?.project_path,
             container.project().dist_dir().await?
         )),
diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index b1347fd2ef67d..ab10ec4df5533 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -1,4 +1,4 @@
-use std::{path::MAIN_SEPARATOR, time::Duration};
+use std::time::Duration;
 
 use anyhow::{Context, Result, bail};
 use indexmap::map::Entry;
@@ -36,10 +36,7 @@ use turbo_tasks::{
     trace::TraceRawVcs,
 };
 use turbo_tasks_env::{EnvMap, ProcessEnv};
-use turbo_tasks_fs::{
-    DiskFileSystem, FileSystem, FileSystemPath, VirtualFileSystem, get_relative_path_to,
-    invalidation,
-};
+use turbo_tasks_fs::{DiskFileSystem, FileSystem, FileSystemPath, VirtualFileSystem, invalidation};
 use turbopack::{
     ModuleAssetContext, evaluate_context::node_build_environment,
     global_module_ids::get_global_module_id_strategy, transition::TransitionOptions,
@@ -149,11 +146,13 @@ pub struct WatchOptions {
 )]
 #[serde(rename_all = "camelCase")]
 pub struct ProjectOptions {
-    /// A root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail. Think of this as a chroot.
+    /// An absolute root path from which all files must be nested under. Trying to access
+    /// a file outside this root will fail, so think of this as a chroot.
+    /// E.g. `/home/user/projects/my-repo`.
     pub root_path: RcStr,
 
-    /// A path inside the root_path which contains the app/pages directories.
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// E.g. `apps/my-app`
     pub project_path: RcStr,
 
     /// The contents of next.config.js, serialized to JSON.
@@ -538,16 +537,20 @@ impl ProjectContainer {
 
 #[turbo_tasks::value]
 pub struct Project {
-    /// A root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail. Think of this as a chroot.
-    root_path: RcStr,
-
-    /// A path where to emit the build outputs. next.config.js's distDir.
-    dist_dir: RcStr,
+    /// An absolute root path from which all files must be nested under. Trying to access
+    /// a file outside this root will fail, so think of this as a chroot.
+    /// E.g. `/home/user/projects/my-repo`.
+    pub root_path: RcStr,
 
-    /// A path inside the root_path which contains the app/pages directories.
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// E.g. `apps/my-app`
     pub project_path: RcStr,
 
+    /// A path where to emit the build outputs, relative to [`Project::project_path`].
+    /// Corresponds to next.config.js's `distDir`.
+    /// E.g. `.next`
+    dist_dir: RcStr,
+
     /// Filesystem watcher options.
     watch: WatchOptions,
 
@@ -692,14 +695,12 @@ impl Project {
     #[turbo_tasks::function]
     pub async fn node_root(self: Vc<Self>) -> Result<Vc<FileSystemPath>> {
         let this = self.await?;
-        let relative_from_root_to_project_path =
-            get_relative_path_to(&this.root_path, &this.project_path);
         Ok(self
             .output_fs()
             .root()
             .await?
-            .join(&relative_from_root_to_project_path)?
-            .join(&this.dist_dir.clone())?
+            .join(&this.project_path)?
+            .join(&this.dist_dir)?
             .cell())
     }
 
@@ -742,12 +743,7 @@ impl Project {
     pub async fn project_path(self: Vc<Self>) -> Result<Vc<FileSystemPath>> {
         let this = self.await?;
         let root = self.project_root_path().await?;
-        let project_relative = this.project_path.strip_prefix(&*this.root_path).unwrap();
-        let project_relative = project_relative
-            .strip_prefix(MAIN_SEPARATOR)
-            .unwrap_or(project_relative)
-            .replace(MAIN_SEPARATOR, "/");
-        Ok(root.join(&project_relative)?.cell())
+        Ok(root.join(&this.project_path)?.cell())
     }
 
     #[turbo_tasks::function]
diff --git a/packages/next/src/build/swc/types.ts b/packages/next/src/build/swc/types.ts
index 5c3f074d1204d..382653c0d0d96 100644
--- a/packages/next/src/build/swc/types.ts
+++ b/packages/next/src/build/swc/types.ts
@@ -346,13 +346,14 @@ export type WrittenEndpoint =
 
 export interface ProjectOptions {
   /**
-   * A root path from which all files must be nested under. Trying to access
-   * a file outside this root will fail. Think of this as a chroot.
-   */
+   * An absolute root path from which all files must be nested under. Trying to access
+   * a file outside this root will fail, so think of this as a chroot.
+   * E.g. `/home/user/projects/my-repo`. */
   rootPath: string
 
   /**
-   * A path inside the root_path which contains the app/pages directories.
+   * A path which contains the app/pages directories, relative to [`Project::root_path`].
+   * E.g. `apps/my-app`
    */
   projectPath: string
 
diff --git a/packages/next/src/build/turbopack-build/impl.ts b/packages/next/src/build/turbopack-build/impl.ts
index 4f046d7f01e56..391c173ea666a 100644
--- a/packages/next/src/build/turbopack-build/impl.ts
+++ b/packages/next/src/build/turbopack-build/impl.ts
@@ -22,6 +22,7 @@ import { setGlobal } from '../../trace'
 import { isCI } from '../../server/ci-info'
 import { backgroundLogCompilationEvents } from '../../shared/lib/turbopack/compilation-events'
 import { getSupportedBrowsers } from '../utils'
+import { normalizePath } from '../../lib/normalize-path'
 
 export async function turbopackBuild(): Promise<{
   duration: number
@@ -52,10 +53,11 @@ export async function turbopackBuild(): Promise<{
   const supportedBrowsers = getSupportedBrowsers(dir, dev)
 
   const persistentCaching = isPersistentCachingEnabled(config)
+  const rootPath = config.turbopack?.root || config.outputFileTracingRoot || dir
   const project = await bindings.turbo.createProject(
     {
-      projectPath: dir,
       rootPath: config.turbopack?.root || config.outputFileTracingRoot || dir,
+      projectPath: normalizePath(path.relative(rootPath, dir)),
       distDir,
       nextConfig: config,
       jsConfig: await getTurbopackJsConfig(dir, config),
diff --git a/packages/next/src/build/webpack/loaders/css-loader/src/utils.ts b/packages/next/src/build/webpack/loaders/css-loader/src/utils.ts
index 5bea07bcf7a2c..aeb1487cc5e89 100644
--- a/packages/next/src/build/webpack/loaders/css-loader/src/utils.ts
+++ b/packages/next/src/build/webpack/loaders/css-loader/src/utils.ts
@@ -11,6 +11,7 @@ import localByDefault from 'next/dist/compiled/postcss-modules-local-by-default'
 import extractImports from 'next/dist/compiled/postcss-modules-extract-imports'
 import modulesScope from 'next/dist/compiled/postcss-modules-scope'
 import camelCase from './camelcase'
+import { normalizePath } from '../../../../../lib/normalize-path'
 
 const whitespace = '[\\x20\\t\\r\\n\\f]'
 const unescapeRegExp = new RegExp(
@@ -39,10 +40,6 @@ function unescape(str: string) {
   })
 }
 
-function normalizePath(file: string) {
-  return path.sep === '\\' ? file.replace(/\\/g, '/') : file
-}
-
 function fixedEncodeURIComponent(str: string) {
   return str.replace(/[!'()*]/g, (c) => `%${c.charCodeAt(0).toString(16)}`)
 }
diff --git a/packages/next/src/lib/normalize-path.ts b/packages/next/src/lib/normalize-path.ts
new file mode 100644
index 0000000000000..4f9e91f4242f8
--- /dev/null
+++ b/packages/next/src/lib/normalize-path.ts
@@ -0,0 +1,5 @@
+import path from 'path'
+
+export function normalizePath(file: string) {
+  return path.sep === '\\' ? file.replace(/\\/g, '/') : file
+}
diff --git a/packages/next/src/server/dev/hot-reloader-turbopack.ts b/packages/next/src/server/dev/hot-reloader-turbopack.ts
index eec77918c7144..b3c66ed74b8e3 100644
--- a/packages/next/src/server/dev/hot-reloader-turbopack.ts
+++ b/packages/next/src/server/dev/hot-reloader-turbopack.ts
@@ -1,6 +1,6 @@
 import type { Socket } from 'net'
 import { mkdir, writeFile } from 'fs/promises'
-import { join, extname } from 'path'
+import { join, extname, relative } from 'path'
 import { pathToFileURL } from 'url'
 
 import ws from 'next/dist/compiled/ws'
@@ -209,13 +209,14 @@ export async function createHotReloaderTurbopack(
   const supportedBrowsers = getSupportedBrowsers(projectPath, dev)
   const currentNodeJsVersion = process.versions.node
 
+  const rootPath =
+    opts.nextConfig.turbopack?.root ||
+    opts.nextConfig.outputFileTracingRoot ||
+    projectPath
   const project = await bindings.turbo.createProject(
     {
-      projectPath: projectPath,
-      rootPath:
-        opts.nextConfig.turbopack?.root ||
-        opts.nextConfig.outputFileTracingRoot ||
-        projectPath,
+      rootPath,
+      projectPath: relative(rootPath, projectPath),
       distDir,
       nextConfig: opts.nextConfig,
       jsConfig: await getTurbopackJsConfig(projectPath, nextConfig),

From 3b9dbbdd0c23294ecda92cc16e76e0a4b0fa1bf9 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 16:01:09 +0200
Subject: [PATCH 03/10] Fixup

---
 crates/napi/src/next_api/project.rs           | 11 +++------
 crates/next-api/src/project.rs                | 24 +++++++++++++++----
 .../next/src/build/turbopack-build/impl.ts    |  2 +-
 .../src/server/dev/hot-reloader-turbopack.ts  |  3 ++-
 4 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/crates/napi/src/next_api/project.rs b/crates/napi/src/next_api/project.rs
index b36fe0c02042a..0ff0fa94c47a6 100644
--- a/crates/napi/src/next_api/project.rs
+++ b/crates/napi/src/next_api/project.rs
@@ -1426,14 +1426,9 @@ pub async fn get_source_map_rope(
         Err(_) => (file_path.to_string(), None),
     };
 
-    let Some(chunk_base) = file.strip_prefix(
-        &(format!(
-            "{}/{}/{}",
-            container.project().await?.root_path,
-            container.project().await?.project_path,
-            container.project().dist_dir().await?
-        )),
-    ) else {
+    let Some(chunk_base) =
+        file.strip_prefix(container.project().dist_dir_absolute().await?.as_str())
+    else {
         // File doesn't exist within the dist dir
         return Ok(OptionStringifiedSourceMap::none());
     };
diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index ab10ec4df5533..fb92aeca69210 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -36,7 +36,10 @@ use turbo_tasks::{
     trace::TraceRawVcs,
 };
 use turbo_tasks_env::{EnvMap, ProcessEnv};
-use turbo_tasks_fs::{DiskFileSystem, FileSystem, FileSystemPath, VirtualFileSystem, invalidation};
+use turbo_tasks_fs::{
+    DiskFileSystem, FileSystem, FileSystemPath, VirtualFileSystem, invalidation,
+    util::{join_path, unix_to_sys},
+};
 use turbopack::{
     ModuleAssetContext, evaluate_context::node_build_environment,
     global_module_ids::get_global_module_id_strategy, transition::TransitionOptions,
@@ -540,11 +543,11 @@ pub struct Project {
     /// An absolute root path from which all files must be nested under. Trying to access
     /// a file outside this root will fail, so think of this as a chroot.
     /// E.g. `/home/user/projects/my-repo`.
-    pub root_path: RcStr,
+    root_path: RcStr,
 
     /// A path which contains the app/pages directories, relative to [`Project::root_path`].
     /// E.g. `apps/my-app`
-    pub project_path: RcStr,
+    project_path: RcStr,
 
     /// A path where to emit the build outputs, relative to [`Project::project_path`].
     /// Corresponds to next.config.js's `distDir`.
@@ -688,8 +691,19 @@ impl Project {
     }
 
     #[turbo_tasks::function]
-    pub fn dist_dir(&self) -> Vc<RcStr> {
-        Vc::cell(self.dist_dir.clone())
+    pub fn dist_dir_absolute(&self) -> Result<Vc<RcStr>> {
+        Ok(Vc::cell(
+            format!(
+                "{}{}{}",
+                self.root_path,
+                std::path::MAIN_SEPARATOR,
+                unix_to_sys(
+                    &join_path(&self.project_path, &self.dist_dir)
+                        .context("expected project_path to be inside of root_path")?
+                )
+            )
+            .into(),
+        ))
     }
 
     #[turbo_tasks::function]
diff --git a/packages/next/src/build/turbopack-build/impl.ts b/packages/next/src/build/turbopack-build/impl.ts
index 391c173ea666a..b2e86aceea4d6 100644
--- a/packages/next/src/build/turbopack-build/impl.ts
+++ b/packages/next/src/build/turbopack-build/impl.ts
@@ -57,7 +57,7 @@ export async function turbopackBuild(): Promise<{
   const project = await bindings.turbo.createProject(
     {
       rootPath: config.turbopack?.root || config.outputFileTracingRoot || dir,
-      projectPath: normalizePath(path.relative(rootPath, dir)),
+      projectPath: normalizePath(path.relative(rootPath, dir) || '.'),
       distDir,
       nextConfig: config,
       jsConfig: await getTurbopackJsConfig(dir, config),
diff --git a/packages/next/src/server/dev/hot-reloader-turbopack.ts b/packages/next/src/server/dev/hot-reloader-turbopack.ts
index b3c66ed74b8e3..2bb80d8744965 100644
--- a/packages/next/src/server/dev/hot-reloader-turbopack.ts
+++ b/packages/next/src/server/dev/hot-reloader-turbopack.ts
@@ -99,6 +99,7 @@ import { getRestartDevServerMiddleware } from '../../next-devtools/server/restar
 import { backgroundLogCompilationEvents } from '../../shared/lib/turbopack/compilation-events'
 import { getSupportedBrowsers } from '../../build/utils'
 import { receiveBrowserLogsTurbopack } from './browser-logs/receive-logs'
+import { normalizePath } from '../../lib/normalize-path'
 
 const wsServer = new ws.Server({ noServer: true })
 const isTestMode = !!(
@@ -216,7 +217,7 @@ export async function createHotReloaderTurbopack(
   const project = await bindings.turbo.createProject(
     {
       rootPath,
-      projectPath: relative(rootPath, projectPath),
+      projectPath: normalizePath(relative(rootPath, projectPath) || '.'),
       distDir,
       nextConfig: opts.nextConfig,
       jsConfig: await getTurbopackJsConfig(projectPath, nextConfig),

From ce08801e09a08d3a613760c33c827db1410ee0d9 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 16:02:12 +0200
Subject: [PATCH 04/10] Add comment

---
 turbopack/crates/turbo-tasks-fs/src/lib.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/turbopack/crates/turbo-tasks-fs/src/lib.rs b/turbopack/crates/turbo-tasks-fs/src/lib.rs
index a6feed450ecc8..83d718a52b1b2 100644
--- a/turbopack/crates/turbo-tasks-fs/src/lib.rs
+++ b/turbopack/crates/turbo-tasks-fs/src/lib.rs
@@ -997,6 +997,7 @@ impl ValueToString for DiskFileSystem {
     }
 }
 
+/// Note: this only works for Unix-style paths (with `/` as a separator).
 pub fn get_relative_path_to(path: &str, other_path: &str) -> String {
     fn split(s: &str) -> impl Iterator<Item = &str> {
         let empty = s.is_empty();

From 754e1fe8e19c47a8d8baba959c23456c0abaab51 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 16:10:23 +0200
Subject: [PATCH 05/10] Sync comments

---
 crates/napi/src/next_api/project.rs           | 26 +++++++++-------
 .../next/src/build/swc/generated-native.d.ts  | 30 ++++++++++++-------
 packages/next/src/build/swc/types.ts          |  9 ++++--
 3 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/crates/napi/src/next_api/project.rs b/crates/napi/src/next_api/project.rs
index 0ff0fa94c47a6..b8b8c42b66be2 100644
--- a/crates/napi/src/next_api/project.rs
+++ b/crates/napi/src/next_api/project.rs
@@ -126,15 +126,18 @@ pub struct NapiWatchOptions {
 
 #[napi(object)]
 pub struct NapiProjectOptions {
-    /// A root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail. Think of this as a chroot.
+    /// An absolute root path from which all files must be nested under. Trying to access
+    /// a file outside this root will fail, so think of this as a chroot.
+    /// E.g. `/home/user/projects/my-repo`.
     pub root_path: RcStr,
 
-    /// A path inside the root_path which contains the app/pages directories.
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// E.g. `apps/my-app`
     pub project_path: RcStr,
 
-    /// next.config's distDir. Project initialization occurs earlier than
-    /// deserializing next.config, so passing it as separate option.
+    /// A path where to emit the build outputs, relative to [`Project::project_path`].
+    /// Corresponds to next.config.js's `distDir`.
+    /// E.g. `.next`
     pub dist_dir: RcStr,
 
     /// Filesystem watcher options.
@@ -180,15 +183,18 @@ pub struct NapiProjectOptions {
 /// [NapiProjectOptions] with all fields optional.
 #[napi(object)]
 pub struct NapiPartialProjectOptions {
-    /// A root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail. Think of this as a chroot.
+    /// An absolute root path from which all files must be nested under. Trying to access
+    /// a file outside this root will fail, so think of this as a chroot.
+    /// E.g. `/home/user/projects/my-repo`.
     pub root_path: Option<RcStr>,
 
-    /// A path inside the root_path which contains the app/pages directories.
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// E.g. `apps/my-app`
     pub project_path: Option<RcStr>,
 
-    /// next.config's distDir. Project initialization occurs earlier than
-    /// deserializing next.config, so passing it as separate option.
+    /// A path where to emit the build outputs, relative to [`Project::project_path`].
+    /// Corresponds to next.config.js's `distDir`.
+    /// E.g. `.next`
     pub dist_dir: Option<Option<RcStr>>,
 
     /// Filesystem watcher options.
diff --git a/packages/next/src/build/swc/generated-native.d.ts b/packages/next/src/build/swc/generated-native.d.ts
index 85bf4c77681ec..539d828eeba91 100644
--- a/packages/next/src/build/swc/generated-native.d.ts
+++ b/packages/next/src/build/swc/generated-native.d.ts
@@ -100,15 +100,20 @@ export interface NapiWatchOptions {
 }
 export interface NapiProjectOptions {
   /**
-   * A root path from which all files must be nested under. Trying to access
-   * a file outside this root will fail. Think of this as a chroot.
+   * An absolute root path from which all files must be nested under. Trying to access
+   * a file outside this root will fail, so think of this as a chroot.
+   * E.g. `/home/user/projects/my-repo`.
    */
   rootPath: RcStr
-  /** A path inside the root_path which contains the app/pages directories. */
+  /**
+   * A path which contains the app/pages directories, relative to [`Project::root_path`].
+   * E.g. `apps/my-app`
+   */
   projectPath: RcStr
   /**
-   * next.config's distDir. Project initialization occurs earlier than
-   * deserializing next.config, so passing it as separate option.
+   * A path where to emit the build outputs, relative to [`Project::project_path`].
+   * Corresponds to next.config.js's `distDir`.
+   * E.g. `.next`
    */
   distDir: RcStr
   /** Filesystem watcher options. */
@@ -146,15 +151,20 @@ export interface NapiProjectOptions {
 /** [NapiProjectOptions] with all fields optional. */
 export interface NapiPartialProjectOptions {
   /**
-   * A root path from which all files must be nested under. Trying to access
-   * a file outside this root will fail. Think of this as a chroot.
+   * An absolute root path from which all files must be nested under. Trying to access
+   * a file outside this root will fail, so think of this as a chroot.
+   * E.g. `/home/user/projects/my-repo`.
    */
   rootPath?: RcStr
-  /** A path inside the root_path which contains the app/pages directories. */
+  /**
+   * A path which contains the app/pages directories, relative to [`Project::root_path`].
+   * E.g. `apps/my-app`
+   */
   projectPath?: RcStr
   /**
-   * next.config's distDir. Project initialization occurs earlier than
-   * deserializing next.config, so passing it as separate option.
+   * A path where to emit the build outputs, relative to [`Project::project_path`].
+   * Corresponds to next.config.js's `distDir`.
+   * E.g. `.next`
    */
   distDir?: RcStr | undefined | null
   /** Filesystem watcher options. */
diff --git a/packages/next/src/build/swc/types.ts b/packages/next/src/build/swc/types.ts
index 382653c0d0d96..2ccf4a16db543 100644
--- a/packages/next/src/build/swc/types.ts
+++ b/packages/next/src/build/swc/types.ts
@@ -348,17 +348,20 @@ export interface ProjectOptions {
   /**
    * An absolute root path from which all files must be nested under. Trying to access
    * a file outside this root will fail, so think of this as a chroot.
-   * E.g. `/home/user/projects/my-repo`. */
+   * E.g. `/home/user/projects/my-repo`.
+   */
   rootPath: string
 
   /**
-   * A path which contains the app/pages directories, relative to [`Project::root_path`].
+   * A path which contains the app/pages directories, relative to `root_path`.
    * E.g. `apps/my-app`
    */
   projectPath: string
 
   /**
-   * The path to the .next directory.
+   * A path where to emit the build outputs, relative to [`Project::project_path`].
+   * Corresponds to next.config.js's `distDir`.
+   * E.g. `.next`
    */
   distDir: string
 

From e0894b4cc7a38851780009a59443dd4bbf8c20c3 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Thu, 17 Jul 2025 16:50:40 +0200
Subject: [PATCH 06/10] Fix test

---
 crates/next-api/src/project.rs             | 11 +++--------
 test/development/basic/next-rs-api.test.ts | 21 ++++++++-------------
 2 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index fb92aeca69210..47ce6f3d96f63 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -742,15 +742,10 @@ impl Project {
     }
 
     #[turbo_tasks::function]
-    pub async fn node_root_to_root_path(self: Vc<Self>) -> Result<Vc<RcStr>> {
-        let this = self.await?;
-        let output_root_to_root_path = self
-            .project_path()
-            .await?
-            .join(&this.dist_dir.clone())?
-            .get_relative_path_to(&*self.project_root_path().await?)
+    pub async fn node_root_to_root_path(&self) -> Result<Vc<RcStr>> {
+        let output_root_to_root_path = join_path(&self.project_path, &self.dist_dir)
             .context("Project path need to be in root path")?;
-        Ok(Vc::cell(output_root_to_root_path))
+        Ok(Vc::cell(output_root_to_root_path.into()))
     }
 
     #[turbo_tasks::function]
diff --git a/test/development/basic/next-rs-api.test.ts b/test/development/basic/next-rs-api.test.ts
index 714b8b1cf8c37..31785cd9444e4 100644
--- a/test/development/basic/next-rs-api.test.ts
+++ b/test/development/basic/next-rs-api.test.ts
@@ -187,26 +187,21 @@ describe('next.rs api', () => {
   let project: Project
   let projectUpdateSubscription: AsyncIterableIterator<UpdateInfo>
   beforeAll(async () => {
-    console.log(next.testDir)
     const nextConfig = await loadConfig(PHASE_DEVELOPMENT_SERVER, next.testDir)
     const bindings = await loadBindings()
-    const distDir = path.join(
-      process.env.NEXT_SKIP_ISOLATE
-        ? path.resolve(__dirname, '../../..')
-        : next.testDir,
-      '.next'
-    )
+    const rootPath = process.env.NEXT_SKIP_ISOLATE
+      ? path.resolve(__dirname, '../../..')
+      : next.testDir
+    const distDir = '.next'
     project = await bindings.turbo.createProject({
       env: {},
       jsConfig: {
         compilerOptions: {},
       },
       nextConfig: nextConfig,
-      projectPath: next.testDir,
+      rootPath,
+      projectPath: path.relative(rootPath, next.testDir) || '.',
       distDir,
-      rootPath: process.env.NEXT_SKIP_ISOLATE
-        ? path.resolve(__dirname, '../../..')
-        : next.testDir,
       watch: {
         enable: true,
       },
@@ -217,7 +212,7 @@ describe('next.rs api', () => {
         clientRouterFilters: undefined,
         config: nextConfig,
         dev: true,
-        distDir: distDir,
+        distDir: path.join(rootPath, distDir),
         fetchCacheKeyPrefix: undefined,
         hasRewrites: false,
         middlewareMatchers: undefined,
@@ -265,7 +260,7 @@ describe('next.rs api', () => {
     expect(normalizeDiagnostics(entrypoints.value.diagnostics)).toMatchSnapshot(
       'diagnostics'
     )
-    entrypointsSubscription.return()
+    await entrypointsSubscription.return()
   })
 
   const routes = [

From 4a0a8fd2d6b29de60296d27781678a480906b0ac Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Fri, 18 Jul 2025 09:23:19 +0200
Subject: [PATCH 07/10] Fix comment

---
 crates/next-api/src/project.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index 47ce6f3d96f63..f4f15e2070737 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -154,7 +154,7 @@ pub struct ProjectOptions {
     /// E.g. `/home/user/projects/my-repo`.
     pub root_path: RcStr,
 
-    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// A path which contains the app/pages directories, relative to [`ProjectOptions::root_path`].
     /// E.g. `apps/my-app`
     pub project_path: RcStr,
 

From 97d0ad2de521c734e1ae2613395727039d4d2210 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Fri, 18 Jul 2025 09:39:44 +0200
Subject: [PATCH 08/10] Fix node_root_to_root_path

---
 crates/next-api/src/project.rs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index f4f15e2070737..67e667e16f816 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -741,11 +741,17 @@ impl Project {
             .cell())
     }
 
+    /// Returns the relative path from the node root to the output root.
+    /// E.g. from `[project]/test/e2e/app-dir/non-root-project-monorepo/apps/web/app/
+    /// import-meta-url-ssr/page.tsx` to `[project]/`.
     #[turbo_tasks::function]
-    pub async fn node_root_to_root_path(&self) -> Result<Vc<RcStr>> {
-        let output_root_to_root_path = join_path(&self.project_path, &self.dist_dir)
-            .context("Project path need to be in root path")?;
-        Ok(Vc::cell(output_root_to_root_path.into()))
+    pub async fn node_root_to_root_path(self: Vc<Self>) -> Result<Vc<RcStr>> {
+        Ok(Vc::cell(
+            self.node_root()
+                .await?
+                .get_relative_path_to(&*self.output_fs().root().await?)
+                .context("Expected node root to be inside of output fs")?,
+        ))
     }
 
     #[turbo_tasks::function]

From f9ffa446405eeee0747064eba10c5c13ba9b722e Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Fri, 18 Jul 2025 10:04:19 +0200
Subject: [PATCH 09/10] Fixup

---
 packages/next/src/build/swc/index.ts                       | 7 +++++--
 .../next/src/server/lib/router-utils/setup-dev-bundler.ts  | 7 +++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/packages/next/src/build/swc/index.ts b/packages/next/src/build/swc/index.ts
index 910e9c9fc84f3..0299b04ad697a 100644
--- a/packages/next/src/build/swc/index.ts
+++ b/packages/next/src/build/swc/index.ts
@@ -621,7 +621,7 @@ function bindingToApi(
       ...options,
       nextConfig: await serializeNextConfig(
         options.nextConfig,
-        options.projectPath!
+        path.join(options.rootPath, options.projectPath)
       ),
       jsConfig: JSON.stringify(options.jsConfig),
       env: rustifyEnv(options.env),
@@ -635,7 +635,10 @@ function bindingToApi(
       ...options,
       nextConfig:
         options.nextConfig &&
-        (await serializeNextConfig(options.nextConfig, options.projectPath!)),
+        (await serializeNextConfig(
+          options.nextConfig,
+          path.join(options.rootPath!, options.projectPath!)
+        )),
       jsConfig: options.jsConfig && JSON.stringify(options.jsConfig),
       env: options.env && rustifyEnv(options.env),
     }
diff --git a/packages/next/src/server/lib/router-utils/setup-dev-bundler.ts b/packages/next/src/server/lib/router-utils/setup-dev-bundler.ts
index a9c10bc0c9ec7..9fa2953c11a36 100644
--- a/packages/next/src/server/lib/router-utils/setup-dev-bundler.ts
+++ b/packages/next/src/server/lib/router-utils/setup-dev-bundler.ts
@@ -83,6 +83,7 @@ import {
 } from '../../../shared/lib/turbopack/utils'
 import { getDefineEnv } from '../../../build/define-env'
 import { TurbopackInternalError } from '../../../shared/lib/turbopack/internal-error'
+import { normalizePath } from '../../../lib/normalize-path'
 
 export type SetupOpts = {
   renderServer: LazyRenderServerInstance
@@ -664,6 +665,10 @@ async function startWatcher(
             opts.fsChecker.rewrites.beforeFiles.length > 0 ||
             opts.fsChecker.rewrites.fallback.length > 0
 
+          const rootPath =
+            opts.nextConfig.turbopack?.root ||
+            opts.nextConfig.outputFileTracingRoot ||
+            opts.dir
           await hotReloader.turbopackProject.update({
             defineEnv: createDefineEnv({
               isTurbopack: true,
@@ -679,6 +684,8 @@ async function startWatcher(
               projectPath: opts.dir,
               rewrites: opts.fsChecker.rewrites,
             }),
+            rootPath,
+            projectPath: normalizePath(path.relative(rootPath, dir)),
           })
         }
 

From 8a0712d9f71a25c8325574a628617ca1c73d5f42 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Fri, 18 Jul 2025 22:14:08 +0200
Subject: [PATCH 10/10] Update comments

---
 crates/napi/src/next_api/project.rs  | 23 ++++++++++++-----------
 crates/next-api/src/project.rs       | 19 ++++++++++---------
 packages/next/src/build/swc/types.ts | 10 +++++-----
 3 files changed, 27 insertions(+), 25 deletions(-)

diff --git a/crates/napi/src/next_api/project.rs b/crates/napi/src/next_api/project.rs
index b8b8c42b66be2..1e3232b7aac71 100644
--- a/crates/napi/src/next_api/project.rs
+++ b/crates/napi/src/next_api/project.rs
@@ -126,17 +126,17 @@ pub struct NapiWatchOptions {
 
 #[napi(object)]
 pub struct NapiProjectOptions {
-    /// An absolute root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail, so think of this as a chroot.
+    /// An absolute root path (Unix or Windows path) from which all files must be nested under.
+    /// Trying to access a file outside this root will fail, so think of this as a chroot.
     /// E.g. `/home/user/projects/my-repo`.
     pub root_path: RcStr,
 
-    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
-    /// E.g. `apps/my-app`
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`], always
+    /// Unix path. E.g. `apps/my-app`
     pub project_path: RcStr,
 
-    /// A path where to emit the build outputs, relative to [`Project::project_path`].
-    /// Corresponds to next.config.js's `distDir`.
+    /// A path where to emit the build outputs, relative to [`Project::project_path`], always Unix
+    /// path. Corresponds to next.config.js's `distDir`.
     /// E.g. `.next`
     pub dist_dir: RcStr,
 
@@ -183,17 +183,18 @@ pub struct NapiProjectOptions {
 /// [NapiProjectOptions] with all fields optional.
 #[napi(object)]
 pub struct NapiPartialProjectOptions {
-    /// An absolute root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail, so think of this as a chroot.
+    /// An absolute root path  (Unix or Windows path) from which all files must be nested under.
+    /// Trying to access a file outside this root will fail, so think of this as a chroot.
     /// E.g. `/home/user/projects/my-repo`.
     pub root_path: Option<RcStr>,
 
-    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`], always
+    /// a Unix path.
     /// E.g. `apps/my-app`
     pub project_path: Option<RcStr>,
 
-    /// A path where to emit the build outputs, relative to [`Project::project_path`].
-    /// Corresponds to next.config.js's `distDir`.
+    /// A path where to emit the build outputs, relative to [`Project::project_path`], always a
+    /// Unix path. Corresponds to next.config.js's `distDir`.
     /// E.g. `.next`
     pub dist_dir: Option<Option<RcStr>>,
 
diff --git a/crates/next-api/src/project.rs b/crates/next-api/src/project.rs
index 67e667e16f816..7f1f0394ab40c 100644
--- a/crates/next-api/src/project.rs
+++ b/crates/next-api/src/project.rs
@@ -149,13 +149,13 @@ pub struct WatchOptions {
 )]
 #[serde(rename_all = "camelCase")]
 pub struct ProjectOptions {
-    /// An absolute root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail, so think of this as a chroot.
+    /// An absolute root path (Unix or Windows path) from which all files must be nested under.
+    /// Trying to access a file outside this root will fail, so think of this as a chroot.
     /// E.g. `/home/user/projects/my-repo`.
     pub root_path: RcStr,
 
-    /// A path which contains the app/pages directories, relative to [`ProjectOptions::root_path`].
-    /// E.g. `apps/my-app`
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`], always
+    /// Unix path. E.g. `apps/my-app`
     pub project_path: RcStr,
 
     /// The contents of next.config.js, serialized to JSON.
@@ -540,17 +540,18 @@ impl ProjectContainer {
 
 #[turbo_tasks::value]
 pub struct Project {
-    /// An absolute root path from which all files must be nested under. Trying to access
-    /// a file outside this root will fail, so think of this as a chroot.
+    /// An absolute root path (Windows or Unix path) from which all files must be nested under.
+    /// Trying to access a file outside this root will fail, so think of this as a chroot.
     /// E.g. `/home/user/projects/my-repo`.
     root_path: RcStr,
 
-    /// A path which contains the app/pages directories, relative to [`Project::root_path`].
+    /// A path which contains the app/pages directories, relative to [`Project::root_path`], always
+    /// a Unix path.
     /// E.g. `apps/my-app`
     project_path: RcStr,
 
-    /// A path where to emit the build outputs, relative to [`Project::project_path`].
-    /// Corresponds to next.config.js's `distDir`.
+    /// A path where to emit the build outputs, relative to [`Project::project_path`], always a
+    /// Unix path. Corresponds to next.config.js's `distDir`.
     /// E.g. `.next`
     dist_dir: RcStr,
 
diff --git a/packages/next/src/build/swc/types.ts b/packages/next/src/build/swc/types.ts
index 2ccf4a16db543..6af182f331a39 100644
--- a/packages/next/src/build/swc/types.ts
+++ b/packages/next/src/build/swc/types.ts
@@ -346,21 +346,21 @@ export type WrittenEndpoint =
 
 export interface ProjectOptions {
   /**
-   * An absolute root path from which all files must be nested under. Trying to access
-   * a file outside this root will fail, so think of this as a chroot.
+   * An absolute root path (Unix or Windows path) from which all files must be nested under. Trying
+   * to access a file outside this root will fail, so think of this as a chroot.
    * E.g. `/home/user/projects/my-repo`.
    */
   rootPath: string
 
   /**
-   * A path which contains the app/pages directories, relative to `root_path`.
+   * A path which contains the app/pages directories, relative to `root_path`, always a Unix path.
    * E.g. `apps/my-app`
    */
   projectPath: string
 
   /**
-   * A path where to emit the build outputs, relative to [`Project::project_path`].
-   * Corresponds to next.config.js's `distDir`.
+   * A path where to emit the build outputs, relative to [`Project::project_path`], always a Unix
+   * path. Corresponds to next.config.js's `distDir`.
    * E.g. `.next`
    */
   distDir: string