From ace08ba642361d57268b1f102c371b060a1f9a2c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Tue, 23 Dec 2025 23:44:38 -0800
Subject: [PATCH] std.Io.Threaded: prevent 0-byte file writes

these cause EINVAL on darwin and are generally a wasted syscall.

and remove a bogus error from File.Writer.Error.
---
 lib/std/Io/File/Writer.zig | 1 -
 lib/std/Io/Threaded.zig    | 8 ++++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/std/Io/File/Writer.zig b/lib/std/Io/File/Writer.zig
index 226b60993f954b7bce70d41c501d35795daacbcf..bf8c0bf289d0313926ad241f60188250635a47dc 100644
--- a/lib/std/Io/File/Writer.zig
+++ b/lib/std/Io/File/Writer.zig
@@ -26,7 +26,6 @@ pub const Error = error{
     InputOutput,
     NoSpaceLeft,
     DeviceBusy,
-    InvalidArgument,
     /// File descriptor does not hold the required rights to write to it.
     AccessDenied,
     PermissionDenied,
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 086139445f737be6e55d594570a9f5f4581ffc11..3662359b31e47c157d570966cec0da355b551e9a 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -7449,6 +7449,8 @@ fn fileWritePositional(
         },
     };
 
+    if (iovlen == 0) return 0;
+
     if (native_os == .wasi and !builtin.link_libc) {
         var n_written: usize = undefined;
         try current_thread.beginSyscall();
@@ -7502,7 +7504,7 @@ fn fileWritePositional(
             else => |e| {
                 current_thread.endSyscall();
                 switch (e) {
-                    .INVAL => return error.InvalidArgument,
+                    .INVAL => |err| return errnoBug(err),
                     .FAULT => |err| return errnoBug(err),
                     .AGAIN => return error.WouldBlock,
                     .BADF => return error.NotOpenForWriting, // Usually a race condition.
@@ -7569,6 +7571,8 @@ fn fileWriteStreaming(
         },
     };
 
+    if (iovlen == 0) return 0;
+
     if (native_os == .wasi and !builtin.link_libc) {
         var n_written: usize = undefined;
         try current_thread.beginSyscall();
@@ -7619,7 +7623,7 @@ fn fileWriteStreaming(
             else => |e| {
                 current_thread.endSyscall();
                 switch (e) {
-                    .INVAL => return error.InvalidArgument,
+                    .INVAL => |err| return errnoBug(err),
                     .FAULT => |err| return errnoBug(err),
                     .AGAIN => return error.WouldBlock,
                     .BADF => return error.NotOpenForWriting, // Can be a race condition.
-- 
2.54.0