From 36a340985ae7e5ec52ec1def4a2885ba49c045cb Mon Sep 17 00:00:00 2001
From: gustav-fff <286169375+gustav-fff@users.noreply.github.com>
Date: Thu, 2 Jul 2026 15:13:53 -0700
Subject: [PATCH] fix(log): create log file when arming SIGSEGV handler fd
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sigsegv::set_log_fd() runs before init_tracing opens/creates the
writer file. Its previous OpenOptions used append(true) with no
create(true), so on the first-ever session the file did not yet
exist, the open failed silently, and LOG_FD stayed -1. When a
segfault later fired the banner was written to fd 2 only; nvim
discards stderr, and nothing ever hit the log — leaving users
with only the terminal banner and no attachable crash section.

Refs #641.
---
 crates/fff-core/src/log.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/crates/fff-core/src/log.rs b/crates/fff-core/src/log.rs
index 13d3cc452..1e586480c 100644
--- a/crates/fff-core/src/log.rs
+++ b/crates/fff-core/src/log.rs
@@ -34,8 +34,15 @@ mod sigsegv {
 
     static LOG_FD: AtomicI32 = AtomicI32::new(-1);
 
+    // Must `create(true)` — this runs before init_tracing opens/creates the
+    // writer file, so an append-only open on a non-existent path silently
+    // fails, LOG_FD stays -1, and the SIGSEGV banner never reaches the log.
     pub fn set_log_fd(path: &Path) {
-        if let Ok(file) = std::fs::OpenOptions::new().append(true).open(path) {
+        if let Ok(file) = std::fs::OpenOptions::new()
+            .create(true)
+            .append(true)
+            .open(path)
+        {
             let prev = LOG_FD.swap(file.into_raw_fd(), Ordering::Relaxed);
             if prev >= 0 {
                 unsafe { libc::close(prev) };