From aacf8ce03d2b52e52830873c40eabb1cb1eb8272 Mon Sep 17 00:00:00 2001
From: Jake Greenfield <jake@greenfield.sh>
Date: Sun, 1 Feb 2026 22:04:20 -0500
Subject: [PATCH] Use MultiReader in `zig std`

---
 lib/compiler/std-docs.zig | 42 +++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/lib/compiler/std-docs.zig b/lib/compiler/std-docs.zig
index 55f49c44e27d2aef6d0a7d513317454f1a3a44d2..72a8c74ff2ce89925f087a32517453b612226b43 100644
--- a/lib/compiler/std-docs.zig
+++ b/lib/compiler/std-docs.zig
@@ -324,11 +324,10 @@ fn buildWasmBinary(
         .stderr = .pipe,
     });
 
-    var poller = Io.poll(gpa, enum { stdout, stderr }, .{
-        .stdout = child.stdout.?,
-        .stderr = child.stderr.?,
-    });
-    defer poller.deinit();
+    var multi_reader_buffer: Io.File.MultiReader.Buffer(2) = undefined;
+    var multi_reader: Io.File.MultiReader = undefined;
+    multi_reader.init(gpa, io, multi_reader_buffer.toStreams(), &.{ child.stdout.?, child.stderr.? });
+    defer multi_reader.deinit();
 
     try sendMessage(io, child.stdin.?, .update);
     try sendMessage(io, child.stdin.?, .exit);
@@ -336,14 +335,23 @@ fn buildWasmBinary(
     var result: ?Cache.Path = null;
     var result_error_bundle = std.zig.ErrorBundle.empty;
 
-    const stdout = poller.reader(.stdout);
+    const stdout = multi_reader.fileReader(0);
+    const MessageHeader = std.zig.Server.Message.Header;
 
-    poll: while (true) {
-        const Header = std.zig.Server.Message.Header;
-        while (stdout.buffered().len < @sizeOf(Header)) if (!try poller.poll()) break :poll;
-        const header = stdout.takeStruct(Header, .little) catch unreachable;
-        while (stdout.buffered().len < header.bytes_len) if (!try poller.poll()) break :poll;
-        const body = stdout.take(header.bytes_len) catch unreachable;
+    var eos_err: error{EndOfStream}!void = {};
+
+    while (true) {
+        const header = stdout.interface.takeStruct(MessageHeader, .little) catch |err| switch (err) {
+            error.EndOfStream => break,
+            error.ReadFailed => return stdout.err.?,
+        };
+        const body = stdout.interface.take(header.bytes_len) catch |err| switch (err) {
+            error.EndOfStream => |e| {
+                eos_err = e;
+                break;
+            },
+            error.ReadFailed => return stdout.err.?,
+        };
 
         switch (header.tag) {
             .zig_version => {
@@ -372,11 +380,15 @@ fn buildWasmBinary(
         }
     }
 
-    const stderr = poller.reader(.stderr);
-    if (stderr.bufferedLen() > 0) {
-        std.debug.print("{s}", .{stderr.buffered()});
+    try multi_reader.fillRemaining(.none);
+    const stderr = multi_reader.reader(1).buffered();
+
+    if (stderr.len > 0) {
+        std.debug.print("{s}", .{stderr});
     }
 
+    try eos_err;
+
     // Send EOF to stdin.
     child.stdin.?.close(io);
     child.stdin = null;
-- 
2.54.0