From 9589c2d5029835e20117c270ccd1ded80f6ad5e9 Mon Sep 17 00:00:00 2001
From: Aditya Singh <adisin650@gmail.com>
Date: Fri, 29 May 2026 00:43:58 -0700
Subject: [PATCH] Replace precondition with fatalError for missing permissions
 on .create

FileDescriptor.open traps when options contains .create but permissions
is nil. The previous precondition could elide its message in optimized
builds, leaving users to hunt through source to diagnose the crash.
Use fatalError with a descriptive message so the reason is always
present in the crash dump, and document the trapping behavior.

Fixes #78
---
 Sources/System/FileOperations.swift | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/Sources/System/FileOperations.swift b/Sources/System/FileOperations.swift
index 9ddc16c3..71ea6e21 100644
--- a/Sources/System/FileOperations.swift
+++ b/Sources/System/FileOperations.swift
@@ -16,6 +16,8 @@ extension FileDescriptor {
   ///   - mode: The read and write access to use.
   ///   - options: The behavior for opening the file.
   ///   - permissions: The file permissions to use for created files.
+  ///     This value must not be `nil` when `options` contains `.create`;
+  ///     passing `nil` in that case is a programmer error and traps at runtime.
   ///   - retryOnInterrupt: Whether to retry the open operation
   ///     if it throws ``Errno/interrupted``.
   ///     The default is `true`.
@@ -55,6 +57,8 @@ extension FileDescriptor {
   ///   - mode: The read and write access to use.
   ///   - options: The behavior for opening the file.
   ///   - permissions: The file permissions to use for created files.
+  ///     This value must not be `nil` when `options` contains `.create`;
+  ///     passing `nil` in that case is a programmer error and traps at runtime.
   ///   - retryOnInterrupt: Whether to retry the open operation
   ///     if it throws ``Errno/interrupted``.
   ///     The default is `true`.
@@ -88,8 +92,10 @@ extension FileDescriptor {
       if let permissions = permissions {
         return system_open(path, oFlag, permissions.rawValue)
       }
-      precondition(!options.contains(.create),
-        "Create must be given permissions")
+      if options.contains(.create) {
+        fatalError(
+          "FileDescriptor.open: 'permissions' must not be nil when 'options' contains '.create'")
+      }
       return system_open(path, oFlag)
     }
     return descOrError.map { FileDescriptor(rawValue: $0) }
@@ -102,6 +108,8 @@ extension FileDescriptor {
   ///   - mode: The read and write access to use.
   ///   - options: The behavior for opening the file.
   ///   - permissions: The file permissions to use for created files.
+  ///     This value must not be `nil` when `options` contains `.create`;
+  ///     passing `nil` in that case is a programmer error and traps at runtime.
   ///   - retryOnInterrupt: Whether to retry the open operation
   ///     if it throws ``Errno/interrupted``.
   ///     The default is `true`.