From 49a258c0e00d8221d088d283a4bd4fb7b0f6b21f Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Tue, 24 Mar 2026 06:23:56 -0400
Subject: [PATCH] std.Build.Step.Run: improve syscalls while running zig test
 executables

Previously, each message requires an unseekable error to be returned
from a syscall before proceeding.  Ideally, the code would just pass
around `*std.Io.Writer` instead of `std.Io.File` in the first place, but
even then, you could argue for saving a syscall with `writerStreaming`.
---
 lib/std/Build/Step/Run.zig | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/std/Build/Step/Run.zig b/lib/std/Build/Step/Run.zig
index 6eb7af603dd1db5506ce97e6d6a14190f46d1c33..3ed4cb2e91bcbacba4326cf81f783d42b9202a22 100644
--- a/lib/std/Build/Step/Run.zig
+++ b/lib/std/Build/Step/Run.zig
@@ -2126,7 +2126,7 @@ fn sendMessage(io: Io, file: Io.File, tag: std.zig.Client.Message.Tag) !void {
         .tag = tag,
         .bytes_len = 0,
     };
-    var w = file.writer(io, &.{});
+    var w = file.writerStreaming(io, &.{});
     w.interface.writeStruct(header, .little) catch |err| switch (err) {
         error.WriteFailed => return w.err.?,
     };
@@ -2137,7 +2137,7 @@ fn sendRunTestMessage(io: Io, file: Io.File, tag: std.zig.Client.Message.Tag, in
         .tag = tag,
         .bytes_len = 4,
     };
-    var w = file.writer(io, &.{});
+    var w = file.writerStreaming(io, &.{});
     w.interface.writeStruct(header, .little) catch |err| switch (err) {
         error.WriteFailed => return w.err.?,
     };
@@ -2157,7 +2157,7 @@ fn sendRunFuzzTestMessage(
         .tag = .start_fuzzing,
         .bytes_len = 4 + 1 + 8,
     };
-    var w = file.writer(io, &.{});
+    var w = file.writerStreaming(io, &.{});
     w.interface.writeStruct(header, .little) catch |err| switch (err) {
         error.WriteFailed => return w.err.?,
     };
@@ -2202,7 +2202,7 @@ fn evalGeneric(run: *Run, spawn_options: process.SpawnOptions) !EvalGenericResul
             var read_buffer: [1024]u8 = undefined;
             var file_reader = file.reader(io, &read_buffer);
             var write_buffer: [1024]u8 = undefined;
-            var stdin_writer = child.stdin.?.writer(io, &write_buffer);
+            var stdin_writer = child.stdin.?.writerStreaming(io, &write_buffer);
             _ = stdin_writer.interface.sendFileAll(&file_reader, .unlimited) catch |err| switch (err) {
                 error.ReadFailed => return run.step.fail("failed to read from {f}: {t}", .{
                     path, file_reader.err.?,
-- 
2.54.0