Implementing interface in PowerShell class does not warn about non-implemented interface members

[ThomasNieto]

System Details

System Details Output

### VSCode version: 1.47.3 91899dcef7b8110878ea59626991a18c8a6a1b3e x64

### VSCode extensions:
DavidAnson.vscode-markdownlint@0.36.2
eamodio.gitlens@10.2.2
Fudge.auto-using@0.7.15
jchannon.csharpextensions@1.3.1
k--kato.docomment@0.1.17
mhutchie.git-graph@1.25.0
ms-azuretools.vscode-docker@1.4.1
ms-dotnettools.csharp@1.22.1
ms-vscode-remote.remote-wsl@0.44.4
ms-vscode.cpptools@0.29.0
ms-vscode.powershell@2020.6.0
ms-vscode.powershell-preview@2020.7.0
redhat.vscode-xml@0.13.0
streetsidesoftware.code-spell-checker@1.9.0
zhuangtongfa.material-theme@3.8.5


### PSES version: 2.3.0.0

### PowerShell version:

Name                           Value
----                           -----
PSVersion                      7.1.0-preview.5
PSEdition                      Core
GitCommitId                    7.1.0-preview.5
OS                             Microsoft Windows 10.0.19041
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Issue Description

PowerShell class implementing an interface does not create an error if required interface members are not present. There is also not a code action to implement interface.

using namespace System.Management.Automation

class test : IArgumentCompleter
{

}

Expected Behaviour

VS code warns about non-implemented interface members like C#. Code action to implement interface.

Actual Behaviour

VS code does not warn about non-implemented interface members or show code action to resolve.

Attached Logs

Follow the instructions in the troubleshooting docs
about capturing and sending logs.

[SeeminglyScience]

That'd be pretty challenging to do well. The exception you get for non-implemented members actually comes at type generation time. So in order for the extension to implement that (without trying to generate the type every key stroke) it would require a pretty significant amount of infrastructure. It would need:

1. Look at the TypeDefinitionAst and inspect the parent types
2. Crawl them via reflection for abstract/interface methods
3. Crawl method definition ASTs and match up their signatures to see what's missing

or show code action to resolve.

FWIW the latest preview of EditorServicesCommandSuite has a "Implement Abstract Class" refactor that is available when you press your Invoke-DocumentRefactor shortcut while the cursor is within the interface name. It produces this:

using namespace System
using namespace System.Collections
using namespace System.Collections.Generic
using namespace System.Management.Automation
using namespace System.Management.Automation.Language

class test : IArgumentCompleter {
    [IEnumerable[CompletionResult]] CompleteArgument([string] $commandName, [string] $parameterName, [string] $wordToComplete, [CommandAst] $commandAst, [IDictionary] $fakeBoundParameters) {
        throw [NotImplementedException]::new()
    }
}

[rjmholt]

This would make the most sense as a PSScriptAnalyzer rule I think

[ThomasNieto]

It would be nice to have that document refactor command included in the extension as a code action when selecting an interface or abstract class.