Generated sources should not be writable

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

Create a build tool that generates a swift source file containing a syntax error. swift build. The error comes up in the generated source file, which developers will invariably edit to fix the error.

The obvious workaround, make the generated file read-only, doesn't work because when the file is regenerated, SPM wants to copy the file into a bundle and will fail to write over the old file when write permissions don't allow it.

Expected behavior

The error shows up in a read-only file.

Actual behavior

I get a writable file.

Steps to reproduce

Create a build tool that generates a swift source file containing a syntax error. swift build. The error comes up in the generated source file, which developers will invariably edit to fix the error.

Swift Package Manager version/commit hash

Swift Package Manager - Swift 6.3.3

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

swift-driver version: 1.148.6 Apple Swift version 6.3.3 (swiftlang-6.3.3.1.3 clang-2100.1.1.101) Target: arm64-apple-macosx26.0 Darwin Mac.localdomain 25.5.0 Darwin Kernel Version 25.5.0: Tue Jun 9 22:28:34 PDT 2026; root:xnu-12377.121.10~1/RELEASE_ARM64_T6041 arm64