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Do not discover assemblies loaded by Assembly.LoadFile #18047

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@daxian-dbw daxian-dbw commented Sep 7, 2022

PR Summary

For modules that target both Windows PowerShell and PowerShell Core, they are usually built against either netstandard2.0, or net462, so that one single set of assemblies can work on both .NET Framework and .NET Core.

For those modules, the API Assembly.LoadFile is usually used to load a dependency assembly into a separate load context when working in PowerShell Core to isolate the dependency, so as to avoid assembly loading conflicts with other modules. This usually happens when the dependency is commonly used by modules, such as Newtonsoft.Json and YamlDotNet.

Today, assemblies loaded by Assembly.LoadFile are discoverable by PowerShell's type resolution, and this breaks the isolation those modules are looking for when using Assembly.LoadFile. Since they are built against netstandard2.0 and net462, they cannot use the AssemblyLoadContext APIs for creating a custom load context but have to depend on Assembly.LoadFile which loads an assembly in a separate assembly load context.

This PR is a breaking change.

PR Context

Assemblies loaded by Assembly.LoadFile are made discoverable by #12203.
However, the original issues that PR was to address is just for assemblies loaded from memory by Assembly.Load(byte[]), and Assembly.LoadFile was never the ask.

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This PR has 17 quantified lines of changes. In general, a change size of upto 200 lines is ideal for the best PR experience!

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Label      : Extra Small
Size       : +11 -6
Percentile : 6.8%

Total files changed: 2

Change summary by file extension:
.cs : +4 -2
.ps1 : +7 -4

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@ghost ghost assigned iSazonov Sep 7, 2022
@iSazonov iSazonov added CL-General Indicates that a PR should be marked as a general cmdlet change in the Change Log CL-BreakingChange Indicates that a PR should be marked as a breaking change in the Change Log labels Sep 7, 2022
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daxian-dbw commented Sep 7, 2022

I'm not sure if we want to make this breaking change, given that it has been the way it works since PowerShell 6.
We can keep the existing behavior, and discourage using Assembly.LoadFile for dependency isolation. @SeeminglyScience, what's your thoughts on this?

@daxian-dbw daxian-dbw closed this Sep 7, 2022
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daxian-dbw commented Sep 7, 2022 •
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I think it's better to keep the current behavior unchanged. For modules built against netstandard2.0 or net462, we can have a AssemblyLoadContextProxy type that wraps some simple reflection APIs to create a custom ALC and load an assembly by path to that ALC. See the following as an example:
https://github.com/PowerShell/platyPS/blob/8ca28935c376ae8dc36ac142e4960fc6d3b725e5/src/ModuleInitAndCleanup.cs#L74-L103

@daxian-dbw daxian-dbw deleted the load branch September 7, 2022 16:50
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iSazonov commented Sep 8, 2022

It seems general question is - should Engine use only default ALC for PowerShell's type resolution? Maybe it makes sense to make this configurable?

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daxian-dbw commented Sep 8, 2022 •
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should Engine use only default ALC for PowerShell's type resolution?

It definitely needs to resolve types from assemblies loaded by Assembly.Load(byte[]). Many users depend on it.

Even though there is no report on Assembly.LoadFile when the regression was introduced by #11088, types from assemblies loaded by Assembly.LoadFile can be resolved by PowerShell in all prior versions of PowerShell Core (and I think it's the same to Windows PowerShell, but didn't verify). I don't think it's a breaking change that we can accept, and hence close this PR.

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