Support PowerShell v3 and v4

[daviwil]

Currently we support only PowerShell v5 but it wouldn't take a great deal of effort to support PowerShell 3 and 4. PoshTools has accomplished this already so there's some work there to be learned from.

The newly released PowerShell reference assemblies could help build version-specific implementation DLLs: http://blogs.msdn.com/b/powershell/archive/2015/12/12/powershell-sdk-reference-assemblies-available-via-nuget-org.aspx

[adamdriscoll]

I'm curious your thoughts on how this will be accomplished. In PoshTools, it really isn't doing anything with S.M.A.dlls. It's more lucky that the assembly version didn't change and we do some checking to prevent MissingMethodExceptions. I think this will eventually lead to a problem if the version does change so it would be good to figure out a way to accomplish it correctly.

One thing that is done via AppVeyor is to build 2013 and 2015 extensions. This is done using some custom MSBuild targets\props.

Are you thinking that we would have different project files or do something similar with custom MSBuild targets? I think the latter would keep the VS solution tidy but is a little more work. The one thing I'm a bit unclear about would be the packages.config file. It seems like we'd need a separate one for each build type or have it patched before package restore kicks in.

I'm sure I'm just totally overthinking this. :)

[daviwil]

The way you've done it is probably the best way to do it for now. For PowerShell v3 through v5 we can probably use the same implementation DLL. If for some reason we have a different SMA assembly version in the future which breaks compatibility with previous code contracts, we'll need to have a different core logic assembly for Editor Services that we hide behind a well-defined interface.

Here's a potential design:

• Microsoft.PowerShell.EditorServices.dll shifts from providing implementations for all features to defining the core feature interfaces that the Editor Services library exposes. It would also provide the library 'lifetime' code that simplifies the use of feature implementations for any version. The caller would specify which implementation assembly to use when they create a new EditorSession.
• Introduce Microsoft.PowerShell.EditorServices.v345.dll which contains the feature implementations that were previously found in the core DLL.
• There could potentially be some 'common' DLL that could share any feature implementations that are version-independent but I'm not sure how likely (or easy) that will be. This would be used as a dependency to every version-specific implementation assembly.
• The Microsoft.PowerShell.EditorServices.Host.exe project would add a new parameter which allows the caller to specify the path to an implementation DLL to use. This would allow a host to be shipped with multiple implementation DLLs that can be selected by the user on a per-session basis.

I don't think we need to go down this road until it's totally necessary, though. For now it's probably more than sufficient to take a similar approach to PoshTools and just be tolerant of whatever PS version is present.

One place where this might become necessary is with PowerShell running on Nano Server. Pretty soon I'll try to convert the codebase over to the new project.json system so that we can build for both full .NET and CoreCLR. I suspect we may have to deal with some interface differences there, but I'm not entirely sure yet.

Let me know what you think!

[daviwil]

Adam's PR has solved this by making sure we can compile correctly against the v3 and v4 PowerShell reference assemblies.

One last thing needs to happen before we can smoothly support the lower versions: adopt the next PSScriptAnalyzer release which includes PowerShell v3 support.

[daviwil]

Sweet, AppVeyor 2.0 beta supports a build matrix:

http://www.appveyor.com/beta

I'm trying to see what it will take to get the PowerShell account moved over to that so we can do test runs for both PowerShell v3 and v5 :)

[adamdriscoll]

That would be awesome! That is something I always wanted to do with PoshTools. It's great that AppVeyor supports that now!

[daviwil]

Just tried the latest PowerShell Editor Services on a machine with PowerShell v3 and it crashes immediately with a MissingMethodException:

Unhandled Exception: System.MissingMethodException: Method not found: 'Void System.Management.Automation.Debugger.SetDebugMode(System.Management.Automation.DebugModes)'.
   at Microsoft.PowerShell.EditorServices.PowerShellContext.Initialize(Runspace initialRunspace)
   at Microsoft.PowerShell.EditorServices.PowerShellContext..ctor()
   at Microsoft.PowerShell.EditorServices.EditorSession.StartSession()
   at Microsoft.PowerShell.EditorServices.Protocol.Server.LanguageServer..ctor(ChannelBase serverChannel)
   at Microsoft.PowerShell.EditorServices.Protocol.Server.LanguageServer..ctor()
   at Microsoft.PowerShell.EditorServices.Host.Program.Main(String[] args)

We shouldn't be calling this method because there's a version guard around it checking for versions higher than v3. I think that the CLR may still be looking for the method despite it not being called in the code path. I'm going to try to debug the issue and see if I can work around it. If not, we may have to hold off on advertising PowerShell v3 and v4 support until we can resolve the problem.