issue building on case-insensitive file systems

[dave256]

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

This bug is the result of a request from @dschaefer2 responding to this Swift Forums post

Some of my students are using Windows and for one of them we have been able to use the debugger with Swift Packages on Windows using VS Code. It was suggested we try using the command line to rule out issues there. I was uncertain how to debug a regular Swift package using that, but made a package using --type executable and tried that.

Here is the error message we got when building:

Building for debugging...
error: emit-module command failed with exit code 1 (use -v to see invocation)  
<unknown>:0: error: PCH was compiled with module cache path 'C:\Users\zapla\downloads\SCLI\SCLI\.build\x86_64-unknown-windows-msvc\debug\ModuleCache\3GXNRWEOZ3IE1', but the path is currently 'C:\Users\zapla\Downloads\SCLI\SCLI\.build\x86_64-unknown-windows-msvc\debug\ModuleCache\3GXNRWEOZ3IE1'
<unknown>:0: error: missing required module 'SwiftShims'
<unknown>:0: error: PCH was compiled with module cache path 'C:\Users\zapla\downloads\SCLI\SCLI\.build\x86_64-unknown-windows-msvc\debug\ModuleCache\3GXNRWEOZ3IE1', but the path is currently 'C:\Users\zapla\Downloads\SCLI\SCLI\.build\x86_64-unknown-windows-msvc\debug\ModuleCache\3GXNRWEOZ3IE1'
<unknown>:0: error: missing required module 'SwiftShims'

Doug noticed it said "downloads" in the one path and "Downloads" in the other path and asked that a bug be filed about it not working on case insensitive file system.

Expected behavior

It would be nice if it could build correctly on case insensitive file systems.

Actual behavior

It fails to build.

Steps to reproduce

1. Put a Swift package of type executable (or possibly any package type) in a directory on a case insensitive filesystem (such as Windows 11) and use the cd command to cd into the directory containing the package (possibly using the wrong case for one of the directories).
2. swift build
3. error occurs - see above description

Swift Package Manager version/commit hash

sorry I don't have access to this now

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

Again, sorry I don't have access to that computer biw. I believe we've had issues with both Swift 5.10.1 and the August 28th development package for Windows on www.swift.org/install/windows