From 803215bb186cb4a16f2f9552749a18fa384634e6 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Tue, 6 May 2025 21:14:09 -0700
Subject: [PATCH] delete std.io.MultiWriter

instead this use case is better served with passthrough streams. For
instance, hashing writers should support being passed an underlying
writer, and the buffer can go in front of the hasher for optimal code.
---
 lib/std/io.zig              |  3 ---
 lib/std/io/multi_writer.zig | 53 -------------------------------------
 src/main.zig                | 16 +++++++----
 3 files changed, 11 insertions(+), 61 deletions(-)
 delete mode 100644 lib/std/io/multi_writer.zig

diff --git a/lib/std/io.zig b/lib/std/io.zig
index b5ffd06de5..3f214062e4 100644
--- a/lib/std/io.zig
+++ b/lib/std/io.zig
@@ -16,9 +16,6 @@ pub const BufferedReader = @import("io/BufferedReader.zig");
 pub const BufferedWriter = @import("io/BufferedWriter.zig");
 pub const AllocatingWriter = @import("io/AllocatingWriter.zig");
 
-pub const MultiWriter = @import("io/multi_writer.zig").MultiWriter;
-pub const multiWriter = @import("io/multi_writer.zig").multiWriter;
-
 pub const ChangeDetectionStream = @import("io/change_detection_stream.zig").ChangeDetectionStream;
 pub const changeDetectionStream = @import("io/change_detection_stream.zig").changeDetectionStream;
 
diff --git a/lib/std/io/multi_writer.zig b/lib/std/io/multi_writer.zig
deleted file mode 100644
index 385ac98d76..0000000000
--- a/lib/std/io/multi_writer.zig
+++ /dev/null
@@ -1,53 +0,0 @@
-const std = @import("../std.zig");
-const io = std.io;
-
-/// Takes a tuple of streams, and constructs a new stream that writes to all of them
-pub fn MultiWriter(comptime Writers: type) type {
-    comptime var ErrSet = error{};
-    inline for (@typeInfo(Writers).@"struct".fields) |field| {
-        const StreamType = field.type;
-        ErrSet = ErrSet || if (@hasDecl(StreamType, "Error")) StreamType.Error else anyerror;
-    }
-
-    return struct {
-        const Self = @This();
-
-        streams: Writers,
-
-        pub const Error = ErrSet;
-        pub const Writer = io.Writer(*Self, Error, write);
-
-        pub fn writer(self: *Self) Writer {
-            return .{ .context = self };
-        }
-
-        pub fn write(self: *Self, bytes: []const u8) Error!usize {
-            inline for (self.streams) |stream|
-                try stream.writeAll(bytes);
-            return bytes.len;
-        }
-    };
-}
-
-pub fn multiWriter(streams: anytype) MultiWriter(@TypeOf(streams)) {
-    return .{ .streams = streams };
-}
-
-const testing = std.testing;
-
-test "MultiWriter" {
-    var tmp = testing.tmpDir(.{});
-    defer tmp.cleanup();
-    var f = try tmp.dir.createFile("t.txt", .{});
-
-    var buf1: [255]u8 = undefined;
-    var fbs1 = io.fixedBufferStream(&buf1);
-    var buf2: [255]u8 = undefined;
-    var stream = multiWriter(.{ fbs1.writer(), f.writer() });
-
-    try stream.writer().print("HI", .{});
-    f.close();
-
-    try testing.expectEqualSlices(u8, "HI", fbs1.getWritten());
-    try testing.expectEqualSlices(u8, "HI", try tmp.dir.readFile("t.txt", &buf2));
-}
diff --git a/src/main.zig b/src/main.zig
index 7c4a3c1a63..561935035f 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -3331,12 +3331,18 @@ fn buildOutputType(
         // We are providing our own cache key, because this file has nothing
         // to do with the cache manifest.
         var hasher = Cache.Hasher.init("0123456789abcdef");
-        var w = io.multiWriter(.{ f.writer(), hasher.writer() });
-        var fifo = std.fifo.LinearFifo(u8, .{ .Static = 4096 }).init();
-        try fifo.pump(fs.File.stdin().reader().unbuffered(), w.writer().unbuffered());
+        var file_writer = f.writer();
+        var file_writer_bw = file_writer.interface().unbuffered();
+        var hasher_writer = hasher.writer(&file_writer_bw);
+        var buffer: [1000]u8 = undefined;
+        var bw = hasher_writer.interface().buffered(&buffer);
+        bw.writeFileAll(.stdin(), .{}) catch |err| switch (err) {
+            error.WriteFailed => fatal("failed to write {s}: {s}", .{ dump_path, file_writer.err.? }),
+            else => fatal("failed to pipe stdin to {s}: {s}", .{ dump_path, err }),
+        };
+        try bw.flush();
 
-        var bin_digest: Cache.BinDigest = undefined;
-        hasher.final(&bin_digest);
+        const bin_digest: Cache.BinDigest = hasher_writer.final();
 
         const sub_path = try std.fmt.allocPrint(arena, "tmp" ++ sep ++ "{x}-stdin{s}", .{
             &bin_digest, ext.canonicalName(target),