From 3f419dd3c0c4186ed34146134faa4432a65aa419 Mon Sep 17 00:00:00 2001
From: Zach Vorhies <zachvorhies@protonmail.com>
Date: Mon, 28 Sep 2026 12:42:08 -0700
Subject: [PATCH] test(esptool): install fake executables by rename to avoid
 ETXTBSY

A sibling test thread forking while a fake esptool was being written
inherited its write fd, so exec failed with 'Text file busy' (flaked
verify_once_reverifies_a_replaced_binary on CI). Write to a staging file
and rename it into place, so the exec'd inode is never open for write.
---
 crates/fbuild-library/src/library/esptool.rs | 28 ++++++++++++--------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/crates/fbuild-library/src/library/esptool.rs b/crates/fbuild-library/src/library/esptool.rs
index e3da3f81..9518a5bb 100644
--- a/crates/fbuild-library/src/library/esptool.rs
+++ b/crates/fbuild-library/src/library/esptool.rs
@@ -733,30 +733,36 @@ mod tests {
 
         let tmp = tempfile::TempDir::new().unwrap();
         let bin = tmp.path().join(esptool_bin_name());
-        std::fs::write(
+        write_script(
             &bin,
-            b"#!/bin/sh\n[ \"$#\" -eq 1 ] && [ \"$1\" = \"version\" ]\n",
-        )
-        .unwrap();
-        fbuild_core::platform::fs::set_executable(&bin).unwrap();
+            "#!/bin/sh\n[ \"$#\" -eq 1 ] && [ \"$1\" = \"version\" ]\n",
+        );
 
         verify_esptool_binary(&bin).await.unwrap();
     }
 
     /// A fake esptool that prints `esptool.py v4.5.1` and appends a line to
     /// `calls` on every run, so tests can count spawns.
+    /// Install an executable script without ever exec'ing a file that is
+    /// open for writing: a sibling test thread forking mid-write inherits
+    /// the write fd, and exec then fails with ETXTBSY.
+    fn write_script(path: &Path, body: &str) {
+        let staging = path.with_extension("staging");
+        std::fs::write(&staging, body).unwrap();
+        fbuild_core::platform::fs::set_executable(&staging).unwrap();
+        std::fs::rename(&staging, path).unwrap();
+    }
+
     fn counting_esptool(dir: &Path) -> (NormalizedPath, NormalizedPath) {
         let bin = NormalizedPath::new(dir.join(esptool_bin_name()));
         let calls = NormalizedPath::new(dir.join("calls"));
-        std::fs::write(
+        write_script(
             &bin,
-            format!(
+            &format!(
                 "#!/bin/sh\necho x >> '{}'\necho 'esptool.py v4.5.1'\n",
                 calls.display()
             ),
-        )
-        .unwrap();
-        fbuild_core::platform::fs::set_executable(&bin).unwrap();
+        );
         (bin, calls)
     }
 
@@ -798,7 +804,7 @@ mod tests {
 
         let mut script = std::fs::read_to_string(&bin).unwrap();
         script.push_str("# replaced\n");
-        std::fs::write(&bin, script).unwrap();
+        write_script(&bin, &script);
         verify_esptool_once(&bin, tmp.path(), None).await.unwrap();
 
         assert_eq!(spawn_count(&calls), 2);