[MinGW] tooling crash on duplicate environment variable names

[RivenSkaye]

Description

On Windows, in shells and environments that allow to differentiate casing on env vars, the swift tooling (swift.exe) crashes on duplicate variable names (e.g. tmp=... and TMP=...).

This is a problem in the case for environments like Git for Windows's Bash shell, MSYS2 environments, etc. where it's nice to just have all tools in one shell instance, for example in order to test code before pushing it.

Reproduction

> TMP="/tmp" tmp="$TMP" swift --version
Swift/NativeDictionary.swift:783: Fatal error: Duplicate values for key: 'ProcessEnvironmentKey(value: "tmp")'
Illegal instruction

# Expected output on a fresh install:
# Swift version 6.1.2 (swift-6.1.2-RELEASE)
# Target: x86_64-unknown-windows-msvc

Stack dump

Swift/NativeDictionary.swift:783: Fatal error: Duplicate values for key: 'ProcessEnvironmentKey(value: "tmp")'
Illegal instruction

Expected behavior

Printing the version information for the compiler and/or other tooling installed

Environment

Swift version 6.1.2 (swift-6.1.2-RELEASE)
MSYSTEM=MINGW64
MSYSTEM_CARCH=x86_64
MSYSTEM_CHOST=x86_64-w64-mingw32
MSYSTEM_PREFIX=/mingw64
tmp=C:\Users\Riven\AppData\Local\Temp
TEMP=/tmp
ORIGINAL_TMP=/c/Users/Martin/AppData/Local/Temp
TMP=/tmp

Additional information

This problem does not exist in a simple cmd.exe session or in PowerShell, where variable name casing is ignored and instead the last definition of the same name is used.

Potential fixes here would be to

• only use the last definition
• only use the first definition
• don't disallow different casing (although this might break existing code if it depends on case insensitivity)

[compnerd]

The environment on Windows is case insensitive as per MSDN. I think that the current behaviour is correct. The MinGW port of Swift is unmaintained, and the Windows port is geared towards native Windows rather than MinGW. Generally speaking, most of the tools have properly started handling this and would treat TMP and tmp as the same variable. Please test with 6.2.

[RivenSkaye]

This is the Windows install of Swift, specifically acquired through winget as per the install instructions. This crash can be triggered through a hard dependency of Swift, as it lists Git for Windows as requirement. Which in turn provides Git Bash, which comes with case sensitive env vars.

I'll try 6.2 tomorrow if it's available through winget and update this reply.

[compnerd]

Sure, it has a dependency on git, but the dependency is not on git bash itself. In fact, there are other issues that bash will often run into (e.g. module loading sometimes behaves slightly differently, but I don't have the exact details as I've not tried to root cause the issues). I would suggest that you run from the supported shell(s): cmd or powershell.

[RivenSkaye]

Forgot to actually run the tests, so just updated and reran on 6.2.1. Alas, the issue still persists. That said, with MSYS2/Cygwin/MinGW being an unsupported use case I think it's fair to place this issue with them instead.