swift build outputs error messages to stdout

[puni073]

Is it reproducible with SwiftPM command-line tools: swift build, swift test, swift package etc?

• Confirmed reproduction steps with SwiftPM CLI. The description text must include reproduction steps with either of command-line SwiftPM commands, swift build, swift test, swift package etc.

Description

Though swiftc outputs error messages to stderr, swift build outputs them to stdout.

Expected behavior

error messages are output to stderr

Actual behavior

error messages are output to stdout

Steps to reproduce

echo 'noprint("Hello, world!")' > Sources/main.swift
swift build

Swift Package Manager version/commit hash

6.0.3

Swift & OS version (output of swift --version ; uname -a)

swift --version

Swift version 6.0.3 (swift-6.0.3-RELEASE)
Target: x86_64-unknown-linux-gnu

cat /etc/lsb-release

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=24.04
DISTRIB_CODENAME=noble
DISTRIB_DESCRIPTION="Ubuntu 24.04.1 LTS"