install: add BUN_DISABLE_SLOW_FILESYSTEM_WARNING, set it in the test harness

scripts/runner.node.mjs

@@ -1784,6 +1784,7 @@ async function spawnBun(execPath, { args, cwd, timeout, gracefulTimeout, idleTim
     FORCE_COLOR: "1",
     BUN_FEATURE_FLAG_INTERNAL_FOR_TESTING: "1",
     BUN_DEBUG_QUIET_LOGS: "1",
+    BUN_DISABLE_SLOW_FILESYSTEM_WARNING: "1",
     BUN_GARBAGE_COLLECTOR_LEVEL: "1",
     BUN_JSC_randomIntegrityAuditRate: "1.0",
     BUN_RUNTIME_TRANSPILER_CACHE_PATH: "0",

src/bun_core/env_var.rs

@@ -234,6 +234,9 @@ pub mod feature_flag {
     // Fall back to the scalar byte-at-a-time VLQ decode in
     // bun_sourcemap::mapping::parse (skips the Highway-dispatched path).
     new_feature_flag!(pub BUN_FEATURE_FLAG_DISABLE_SIMD_SOURCEMAP, "BUN_FEATURE_FLAG_DISABLE_SIMD_SOURCEMAP", {});
+    // Suppress the `bun install` "Slow filesystem detected" warning. Set by the
+    // test harness so stderr assertions don't flake on slow CI filesystems.
+    new_feature_flag!(pub BUN_DISABLE_SLOW_FILESYSTEM_WARNING, "BUN_DISABLE_SLOW_FILESYSTEM_WARNING", {});
     new_feature_flag!(pub BUN_DISABLE_SLOW_LIFECYCLE_SCRIPT_LOGGING, "BUN_DISABLE_SLOW_LIFECYCLE_SCRIPT_LOGGING", {});
     new_feature_flag!(pub BUN_DISABLE_SOURCE_CODE_PREVIEW, "BUN_DISABLE_SOURCE_CODE_PREVIEW", {});
     new_feature_flag!(pub BUN_FEATURE_FLAG_DISABLE_SOURCE_MAPS, "BUN_FEATURE_FLAG_DISABLE_SOURCE_MAPS", {});

src/install/PackageManager/PackageManagerDirectories.rs

@@ -183,7 +183,11 @@ fn get_temporary_directory_run(manager: &mut PackageManager) -> TemporaryDirecto
     let tmpname =
         FileSystem::tmpname(b"hm", &mut tmpbuf, bun_core::fast_random()).expect("unreachable");
 
-    let mut timer = if manager.options.log_level != LogLevel::Silent {
+    let mut timer = if manager.options.log_level != LogLevel::Silent
+        && !bun_core::env_var::feature_flag::BUN_DISABLE_SLOW_FILESYSTEM_WARNING
+            .get()
+            .unwrap_or(false)
+    {
         Some(bun_core::time::Timer::start())
     } else {
         None
@@ -272,8 +276,8 @@ fn get_temporary_directory_run(manager: &mut PackageManager) -> TemporaryDirecto
         break;
     }
 
-    if manager.options.log_level != LogLevel::Silent {
-        let elapsed = timer.as_mut().unwrap().read();
+    if let Some(timer) = timer.as_mut() {
+        let elapsed = timer.read();
         if elapsed > bun_core::time::NS_PER_MS * 100 {
             let mut path_buf = PathBuffer::uninit();
             let cache_dir_path: &[u8] = match sys::get_fd_path(cache_directory_fd, &mut path_buf) {

test/cli/install/bun-run-dir.test.ts

@@ -127,8 +127,8 @@ for (const entry of await decompress(Buffer.from(buffer))) {
       BUN_INSTALL_CACHE_DIR: join(run_dir, ".cache"),
     },
   });
-  const err2 = await new Response(stderr2).text();
-  if (err2) throw new Error(err2);
+  const err2 = stderrForInstall(await new Response(stderr2).text());
+  expect(err2).toBe("");
   expect(await readdirSorted(run_dir)).toEqual([".cache", "test.js"]);
   expect(await readdirSorted(join(run_dir, ".cache"))).toContain("decompress");
   expect(await readdirSorted(join(run_dir, ".cache", "decompress"))).toEqual(["4.2.1@@@1"]);

test/harness.ts

@@ -74,6 +74,9 @@ export const bunEnv: NodeJS.Dict<string> = {
   CI: "1",
   BUN_RUNTIME_TRANSPILER_CACHE_PATH: "0",
   BUN_FEATURE_FLAG_INTERNAL_FOR_TESTING: "1",
+  // The `bun install` "Slow filesystem detected" warning is timing-dependent
+  // and flakes stderr assertions on slow CI filesystems.
+  BUN_DISABLE_SLOW_FILESYSTEM_WARNING: "1",
   // Tests drive `bun update --interactive` by writing keystrokes to a pipe;
   // the real command refuses on non-TTY stdin. Bypass that gate under test.
   BUN_INTERNAL_INTERACTIVE_ASSUME_TTY: "1",
@@ -1513,7 +1516,7 @@ export async function runBunInstall(
 
 // stderr with `slow filesystem` warning removed
 export function stderrForInstall(err: string) {
-  return err.replace(/warn: Slow filesystem.*/g, "");
+  return err.replace(/warn: Slow filesystem.*\r?\n?/g, "");
 }
 
 export async function runBunUpdate(