Fix test fail triggered by multiline environment variables

[stevapple]

Fix TestProcess.test_passthrough_environment fails when an environment variable has multiple lines.

[stevapple]

This is going to fix TestFoundation failures on Azure CI for Windows builds.

CC @compnerd

[MaxDesiatov]

@swift-ci please test

[stevapple]

The Linux test failed, but the failure seems not caused by this change... Could you find the root of it? @MaxDesiatov 😂

[MaxDesiatov]

@swift-ci please test

[stevapple]

Can anyone merge this? I’d like to see the effect on Azure CI.

@MaxDesiatov

[compnerd]

Thanks for looking into this @stevapple. Can you expand the commit message to explain why multi line values don't work? https://docs.microsoft.com/en-us/windows/win32/procthread/environment-variables doesn't seem to indicate the restriction.

[stevapple]

@compnerd It’s not a problem of Windows actually.

First of all, Azure CI environment sometimes contains multiline environment variables, which is really a rare case. The former handler of --env simply print("\(key)=\(value)"), and the parser parses every single line of the output as "key=value", so any extra lines in an environment variable will lead to an error, thus failing the test. What I’m going to do is removing all the newlines characters from value, then the problem will go.

[compnerd]

I guess the question is why does this not impact other platforms? I assume that it is an issue only because it is splitting on the newline?

[stevapple]

It’s because multiline environment variable is really a rare case. A regular machine won’t have that. Azure CI is triggering it because it stores the latest commit message in an environment variable.

I believe the problem will also occur if we manually set an environment variable with multiple lines on Linux and macOS.

[compnerd]

Then, why should this not apply to all targets instead of being windows only? The problem exists in all of the cases it sounds like,

[stevapple]

The patch is applied to all platforms. The #if os(Windows) mark here is to make sure the test is meaningful on Windows because whatever subprocess on Windows will have at least one environment variable.