Bun.build({ compile }): produce the executable on the bundle thread instead of blocking the event loop

src/bundler/BundleThread.rs

@@ -150,6 +150,8 @@ impl<C: CompletionStruct> BundleThread<C> {
         let ptr = SendPtr(instance);
         let thread = std::thread::Builder::new()
             .name("Bundler".into())
+            // `Bun.build({ compile })` writes its executable here; use bun's usual stack.
+            .stack_size(bun_threading::thread_pool::DEFAULT_THREAD_STACK_SIZE as usize)
             .spawn(move || {
                 let ptr = ptr;
                 // SAFETY: caller guarantees `instance` is valid for 'static; `thread_main`

src/options_types/compile_target.rs

@@ -98,7 +98,42 @@ pub enum ParseError {
     InvalidTarget,
 }
 
+/// What downloading a target's executable takes from the env loader, copied out
+/// by [`CompileTarget::download_options`] on the thread that owns the loader so
+/// the download itself can run on another one.
+pub struct DownloadOptions {
+    pub reject_unauthorized: bool,
+    /// Proxy for the registry URL, with `NO_PROXY` already applied.
+    pub http_proxy: Option<Box<[u8]>>,
+}
+
+impl Default for DownloadOptions {
+    /// Placeholder until [`CompileTarget::download_options`] fills it in; verifies TLS.
+    fn default() -> Self {
+        Self {
+            reject_unauthorized: true,
+            http_proxy: None,
+        }
+    }
+}
+
 impl CompileTarget {
+    /// Buffer size callers hand to [`Self::to_npm_registry_url`].
+    pub const REGISTRY_URL_BUF_LEN: usize = 2048;
+
+    pub fn download_options(&self, env: &bun_dotenv::Loader) -> DownloadOptions {
+        let mut url_buf = [0u8; Self::REGISTRY_URL_BUF_LEN];
+        // A URL that cannot be built fails the download itself, which reports it.
+        let http_proxy = self.to_npm_registry_url(&mut url_buf).ok().and_then(|url| {
+            env.get_http_proxy_for(&bun_url::URL::parse(url))
+                .map(|proxy| Box::from(proxy.href))
+        });
+        DownloadOptions {
+            reject_unauthorized: env.get_tls_reject_unauthorized(),
+            http_proxy,
+        }
+    }
+
     pub(crate) fn eql(&self, other: &CompileTarget) -> bool {
         self.os == other.os
             && self.arch == other.arch
@@ -185,7 +220,6 @@ impl CompileTarget {
         &self,
         buf: &'a mut PathBuffer,
         version_str: &'a ZStr,
-        _env: &mut bun_dotenv::Loader,
         needs_download: &mut bool,
     ) -> &'a ZStr {
         if self.is_default() {
@@ -206,7 +240,7 @@ impl CompileTarget {
             return version_str;
         }
 
-        // T1 fallback ignores `_env` (full env-override chain lives in bun_install).
+        // The full cache-dir override chain lives in bun_install; this is its fallback.
         let cache_dir = bun_sys::fetch_cache_directory_path();
         let dest = path::resolve_path::join_abs_string_buf_z::<path::platform::Auto>(
             path::fs::FileSystem::instance().top_level_dir(),

src/runtime/api/JSBundler.rs

@@ -14,7 +14,7 @@ use bun_core::Output;
 use bun_core::{String as BunString, ZigString};
 use bun_jsc::ConcurrentTask::ConcurrentTask;
 use bun_jsc::{self as jsc, CallFrame, JSGlobalObject, JSValue, JsError, JsResult};
-use bun_options_types::compile_target::CompileTarget;
+use bun_options_types::compile_target::{CompileTarget, DownloadOptions};
 use bun_options_types::schema::api; // bun.schema.api
 use bun_standalone_graph::StandaloneModuleGraph;
 
@@ -223,6 +223,8 @@ pub mod js_bundler {
 
     pub struct CompileOptions {
         pub(crate) compile_target: CompileTarget,
+        /// Taken from the VM's env on the calling thread; the download runs on the bundle thread.
+        pub(crate) download: DownloadOptions,
         pub(crate) exec_argv: OwnedString,
         pub(crate) executable_path: OwnedString,
         pub(crate) windows_hide_console: bool,
@@ -244,6 +246,7 @@ pub mod js_bundler {
         fn default() -> Self {
             Self {
                 compile_target: CompileTarget::default(),
+                download: DownloadOptions::default(),
                 exec_argv: OwnedString::default(),
                 executable_path: OwnedString::default(),
                 windows_hide_console: false,
@@ -1197,6 +1200,9 @@ pub mod js_bundler {
                 let is_standalone_html = this.target == Target::Browser && has_all_html_entrypoints;
                 if !is_standalone_html {
                     this.target = Target::Bun;
+                    compile.download = compile
+                        .compile_target
+                        .download_options(global_this.bun_vm().env_loader());
 
                     let define_keys = compile.compile_target.define_keys();
                     let define_values = compile.compile_target.define_values();

src/runtime/api/js_bundle_completion_task.rs

@@ -287,8 +287,8 @@ impl JSBundleCompletionTask {
         Ok(())
     }
 
-    /// Port of `JSBundleCompletionTask.doCompilation`.
-    fn do_compilation(&mut self, output_files: &mut Vec<OutputFile>) -> CompileResult {
+    /// Port of `JSBundleCompletionTask.doCompilation`. Bundle thread: nothing in here may touch JS.
+    fn do_compilation(&self, output_files: &mut Vec<OutputFile>) -> CompileResult {
         let compile_options = self
             .config
             .compile
@@ -426,10 +426,7 @@ impl JSBundleCompletionTask {
             root_dir.fd,
             module_prefix,
             outfile_for_executable,
-            // SAFETY: `self.env` is the per-VM `DotEnv.Loader` stashed at
-            // construction; valid for the lifetime of the VirtualMachine, and
-            // nothing inside `to_executable` reaches it otherwise.
-            unsafe { &mut *self.env },
+            &compile_options.download,
             self.config.format,
             &WindowsOptions {
                 hide_console: compile_options.windows_hide_console,
@@ -559,6 +556,36 @@ impl JSBundleCompletionTask {
         result
     }
 
+    /// `Bun.build({ compile })`: the bundle becomes the executable before `on_complete` gets it.
+    fn compile_on_bundle_thread(&mut self) {
+        if self.config.compile.is_none()
+            || self.cancelled.load(core::sync::atomic::Ordering::Acquire)
+        {
+            return;
+        }
+        let mut build = match core::mem::replace(&mut self.result, BundleV2Result::Pending) {
+            BundleV2Result::Value(build) => build,
+            not_bundled => {
+                self.result = not_bundled;
+                return;
+            }
+        };
+        let compile_result = self.do_compilation(&mut build.output_files);
+        // Nothing else flushes this thread's buffered stderr, which the above reports failures to.
+        bun_core::Output::flush();
+        self.result = match compile_result {
+            CompileResult::Success => BundleV2Result::Value(build),
+            CompileResult::Err(err) => {
+                self.log.add_error_fmt(
+                    None,
+                    bun_ast::Loc::EMPTY,
+                    format_args!("{}", bstr::BStr::new(err.slice())),
+                );
+                BundleV2Result::Err(bun_bundler::Error::CompilationFailed)
+            }
+        };
+    }
+
     pub(crate) fn on_complete_anytask(ctx: *mut Self) -> bun_event_loop::JsResult<()> {
         crate::jsc_hooks::ActiveHandle::Bundle(NonNull::new(ctx).expect("completion")).unregister();
         // For the +1 taken by `complete_on_bundle_thread` enqueue.
@@ -644,7 +671,7 @@ impl JSBundleCompletionTask {
         }
 
         // Copy the BackRef out (it is `Copy`) so `global_this` borrows a local
-        // instead of `*this` — `do_compilation`/`to_js_error` below need `&mut *this`.
+        // instead of `*this` — `to_js_error` below needs `&mut *this`.
         let global_this_ref = this.global_this;
         let global_this = global_this_ref.get();
         // `Strong::swap` ties the returned `&mut JSPromise` to
@@ -654,40 +681,6 @@ impl JSBundleCompletionTask {
         let promise: *mut JSPromise = this.promise.swap();
         let promise = JSPromise::opaque_mut(promise);
 
-        // `do_compilation` borrows `&mut self` while needing
-        // `&mut output_files` from inside `self.result`. Temporarily move the
-        // Vec out via `take` so the method gets a disjoint `&mut self`.
-        if matches!(this.result, BundleV2Result::Value(_)) && this.config.compile.is_some() {
-            let mut output_files = match &mut this.result {
-                BundleV2Result::Value(build) => core::mem::take(&mut build.output_files),
-                // SAFETY: arm checked above.
-                _ => unsafe { core::hint::unreachable_unchecked() },
-            };
-            let compile_result = this.do_compilation(&mut output_files);
-            // `defer compile_result.deinit()` — `CompileResult` is a Rust enum
-            // with owned `Vec<u8>` payloads; drops at end of scope.
-
-            if let CompileResult::Err(err) = &compile_result {
-                // `bun.handleOom(log.addError(..., bun.handleOom(dupe(..))))`
-                this.log.add_error_fmt(
-                    None,
-                    bun_ast::Loc::EMPTY,
-                    format_args!("{}", bstr::BStr::new(err.slice())),
-                );
-                // `this.result.value.deinit()` — owned fields drop with the
-                // overwrite below; `output_files` (moved out above) drops here.
-                drop(output_files);
-                this.result = BundleV2Result::Err(bun_bundler::Error::CompilationFailed);
-            } else {
-                // Put the compacted output_files back.
-                match &mut this.result {
-                    BundleV2Result::Value(build) => build.output_files = output_files,
-                    // SAFETY: arm checked above.
-                    _ => unsafe { core::hint::unreachable_unchecked() },
-                }
-            }
-        }
-
         // `to_js_error` borrows `&mut self`, which would overlap a
         // `&mut this.result` match scrutinee. Dispatch the pending/err arms
         // first, then take a fresh `&mut` for Value.
@@ -1115,6 +1108,7 @@ impl CompletionStruct for JSBundleCompletionTask {
     }
 
     fn complete_on_bundle_thread(&mut self) {
+        self.compile_on_bundle_thread();
         // The bundle thread's last touch of this task and of the VM's memory:
         // hand it back (always queued — the VM waits for it) and stop counting.
         self.bundle_loop

src/runtime/cli/build_command.rs

@@ -889,7 +889,7 @@ impl BuildCommand {
                     &opt_public_path,
                     outfile,
                     // SAFETY: `env` is a process-lifetime singleton.
-                    unsafe { &mut *env_ptr },
+                    &compile_target.download_options(unsafe { &*env_ptr }),
                     opt_output_format,
                     &ctx.bundler_options.windows,
                     ctx.bundler_options

src/standalone_graph/Cargo.toml

@@ -25,7 +25,6 @@ bun_alloc.workspace = true
 bun_core.workspace = true
 bun_bundler.workspace = true
 bun_collections.workspace = true
-bun_dotenv.workspace = true
 bun_exe_format.workspace = true
 bun_http.workspace = true
 bun_parsers.workspace = true

src/standalone_graph/StandaloneModuleGraph.rs

@@ -1646,15 +1646,15 @@ pub(crate) fn inject(
 }
 
 use bun_core::Environment::OperatingSystem as CompileTargetOs;
-pub use bun_options_types::compile_target::CompileTarget;
+pub use bun_options_types::compile_target::{CompileTarget, DownloadOptions};
 
 /// Moved up from `bun_options_types` (T3) so it can name
 /// `bun_http::AsyncHTTP` directly
 /// instead of routing through `extern "Rust"` shims; the only callers are the
 /// two `download*` fns below in this crate.
 pub(crate) fn download_to_path(
     target: &CompileTarget,
-    env: &mut bun_dotenv::Loader,
+    download: &DownloadOptions,
     dest_z: &ZStr,
 ) -> crate::Result<()> {
     bun_http::http_thread::init(&Default::default());
@@ -1666,7 +1666,7 @@ pub(crate) fn download_to_path(
         // TODO: This is way too much code necessary to send a single HTTP request...
         let mut compressed_archive_bytes =
             Box::new(bun_core::MutableString::init(24 * 1024 * 1024)?);
-        let mut url_buffer = [0u8; 2048];
+        let mut url_buffer = [0u8; CompileTarget::REGISTRY_URL_BUF_LEN];
         let url_str = match target.to_npm_registry_url(&mut url_buffer) {
             Ok(s) => s,
             Err(err) => {
@@ -1681,10 +1681,6 @@ pub(crate) fn download_to_path(
             // `progress.end()` below is sufficient: no fallible call sits between
             // `refresher.start` and it, so every exit path (including the
             // error returns after it) ends the node exactly once.
-            // Note: reshaped for borrowck — `get_http_proxy_for` borrows
-            // `env` for the proxy URL lifetime; read the bool first.
-            let reject_unauthorized = env.get_tls_reject_unauthorized();
-            let http_proxy: Option<bun_url::URL<'_>> = env.get_http_proxy_for(&url);
             let progress = refresher.start(b"Downloading", 0);
 
             let mut async_http = Box::new(bun_http::AsyncHTTP::init_sync(
@@ -1693,13 +1689,13 @@ pub(crate) fn download_to_path(
                 Default::default(),
                 b"",
                 b"",
-                http_proxy,
+                download.http_proxy.as_deref().map(bun_url::URL::parse),
                 None,
                 bun_http::FetchRedirect::Follow,
             ));
             async_http.client.progress_node =
                 core::ptr::NonNull::new(core::ptr::from_mut(progress));
-            async_http.client.flags.reject_unauthorized = reject_unauthorized;
+            async_http.client.flags.reject_unauthorized = download.reject_unauthorized;
             let send_result = async_http.send_sync(&mut compressed_archive_bytes);
 
             progress.end();
@@ -1818,7 +1814,7 @@ pub fn to_executable(
     root_dir: Fd,
     module_prefix: &[u8],
     outfile: &[u8],
-    env: &mut bun_dotenv::Loader,
+    download: &DownloadOptions,
     output_format: Format,
     windows_options: &WindowsOptions,
     compile_exec_argv: &[u8],
@@ -1870,10 +1866,10 @@ pub fn to_executable(
         let version_zstr = ZStr::from_slice_with_nul(&version_str[..]);
 
         let mut needs_download: bool = true;
-        let dest_z = target.exe_path(&mut exe_path_buf, version_zstr, env, &mut needs_download);
+        let dest_z = target.exe_path(&mut exe_path_buf, version_zstr, &mut needs_download);
 
         if needs_download {
-            if let Err(e) = download_to_path(target, env, dest_z) {
+            if let Err(e) = download_to_path(target, download, dest_z) {
                 return Ok(match e {
                     crate::Error::TargetNotFound => CompileResult::fail_fmt(format_args!(
                         "Target platform '{}' is not available for download. Check if this version of Bun supports this target.",