Roslyn: Is it possible to add intellisense to dynamic object with something like JSDoc?

[Thaina]

I want to feel like working with javascript object when using dynamic type in C#. And jsdoc approach like salsa from typescript is very neat in my opinion

So I wish C# could be able to do something the same

Is it possible for roslyn to support this feature?

[foxbot]

Supporting low-effort libraries that return dynamic objects, what else could go wrong?

[Thaina]

Well, I heard VisualStudio was support something alike, intellisense on ExpandoObject like this

But it not supported on roslyn. And it not covering my use case

[DustinCampbell]

Note that C# IntelliSense in Visual Studio is part of Roslyn. So, without support in Roslyn, there's no hope for ExpandoObject IntelliSense.

[jveselka]

What I would do is probably something like this
```C#
public class MyDynamicBase : DynamicObject
{
private Dictionary _properties = new Dictionary();

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        return _properties.TryGetValue(binder.Name, out result);
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        if (GetType().GetProperty(binder.Name) != null)
        {
            //you want this to stay sane
            throw new InvalidOperationException("Setting member of incompatible type");
        }
        _properties[binder.Name] = value;
        return true;
    }

    public dynamic More => this;
}

public class MyDynamicObject : MyDynamicBase
{
    public string MyFixedProperty { get; set; }
}

All statically typed stuff goes toMyDynamicObject- Intellisense works as expected. I can set additional properties viamyObject.More.Anything = anything(or by casting to dynamic if you wish) and when I pass it into dynamic API I know thatmyObject.MyFixedPropertyandmyObject.Anything``` are both accessible just fine.

[DustinCampbell]

FWIW, there is an extensibility point for the completion list that you can use to add members to the list: CompletionProvider

[Thaina]

I would like to propose one idea, using interface and generic attribute

Not sure it possible but would be something like this

```C#
interface IUser
{
string UserID { get; set; }
string Name { get; set; }
}

[DynamicProperty]
dynamic obj = LoadUserFromDB();
obj.User :|[intellisense show UserID]|:
```

[Thaina]

@DustinCampbell If I write my own custom CompletionProvider how can I register it to roslyn?

[DustinCampbell]

@Thaina: You don't so much register it with Roslyn as you'd register it with a particular host (such as VS, OmniSharp, etc.), which can be different depending on the host. In VS, integrating a new CompletionProvider would require adding an [ExportCompletionProvider] attribute to it and creating a VS extension that includes it as a MEF component.

[Thaina]

@DustinCampbell I use vscode and omnisharp. Could you please envisioned me how should I get start with?

[DustinCampbell]

Today, there isn't a mechanism for adding anything to OmniSharp's MEF composition without recompiling. You'd need to specifically add your assembly into the set of host assemblies used by OmniSharp. That's set is constructed here. You can provide an IHostExportProvider like they do here

That said, if the feature turns out well, I would hope you'd eventually submit it as a PR to Roslyn. That way, everyone can enjoy it! :smile:

[Thaina]

Thanks for your guide @DustinCampbell

I really wish roslyn itself should be able to add plugin or modulate some parts such as completion and formatting

[DustinCampbell]

How and if extensibility works is really a decision that should be made by the host. Roslyn takes the position that it shouldn't impose an extensibility pattern on an application that hosts Roslyn.

[Thaina]

I'm not sure but I was skim through roslyn and omnisharp source code once and found that completion list was generated from roslyn, am I wrong?

At first I was thinking I could write some plugin on vscode if the list of completion item give me the declaration type of each item and I could get attribute of the field. But it seem omnisharp was proxy all those to roslyn and no additional data was sent to omnisharp, so omnisharp member said that I need to have roslyn add more feature

[DustinCampbell]

Well, I'm both an OmniSharp member and have worked on Roslyn since the beginning. :smile: There are some changes that would need to be done to be able to extend OmniSharp for this purpose. Roslyn provides an API to retrieve that data to display from a completion list. By default, that API will aggregate together the results of a set of completion providers. OmniSharp uses this API today, but only for providing keywords to the completion list. Today, OmniSharp provides symbols to the completion list differently, though that will change in the future (https://github.com/OmniSharp/omnisharp-roslyn/issues/78).

All of that said, this is all open source, so you can feel free to have a go at it.

[DustinCampbell]

Not necessarily. It could be done in many ways, each with different levels of reach:

• It could be coded specifically into OmniSharp's IntelliSense service.
• It could be written as a CompletionProvider in a separate assembly and included in OmniSharp's MEF composition. Once https://github.com/OmniSharp/omnisharp-roslyn/issues/78 is implemented in the future (I'll get back to that someday, I promise!), it would flow through the CompletionService into OmniSharp.
• It could be written as a CompletionProvider and contributed to Roslyn as a PR. This would allow the feature to appear in OmniSharp, VS, and other Roslyn hosts.

That said, whether or not this is doable is unclear. Providing "dynamic" completion statically is super-hard.

[Thaina]

@DustinCampbell My idea is not to analyze all of possible dynamic member statically. Just take the idea from typescript salsa for js that we could mark dynamic object with the known member we want it to be

In vscode we can write js like this

/** @type {{key:string,value:number}[]} */
var keyValuePairs = [];
keyValuePairs[0].va // show intellisense for value as number

So if we could mark dynamic with something

[Dynamic(typeof(IEnumerable<KeyValuePair<string,float>>))]
dynamic keyValuePairs = new Dictionary<string,float>();
keyValuePair.FirstOrDefault().Va // show intellisense for value as float

So I think it doable in the service that

• I can get attribute of that dynamic variable
• I can use reflection to get members of types that implemented on the project
• I can inject those members into completion item list

Which I think roslyn would be a place to do. But would it possible on just @omnisharp-roslyn or just @omnisharp-vscode ?

[DustinCampbell]

Your code example above is a bit confusing. Is keyValuePairs a field? If it's a local, how are you intending to fix an attribute to it? What happens when you continue dotting into members? Will you show extension methods for KeyValuePair<string,float>?

It would be more work to do this in omnisharp-vscode. Because omnisharp-vscode is written in TypeScript and runs on nodejs, you wouldn't be able to write this in C#, or use Roslyn or other managed libraries without other shenanigans. Adding it to omnisharp-roslyn would be the way to go.

[DustinCampbell]

I hope somebody will build a cool tuple-based serialization library for simple data-only cases like this.

```C#
interface IUser
{
string UserID { get; set; }
string Name { get; set; }
}

dynamic obj = LoadUserFromDB();

I'd rather write like this:

```C#
(string usedId, string name) = LoadUserFromDB();

[Thaina]

@DustinCampbell The problem that I wish it must be dynamic because loading object from DB or anywhere dynamic is. It not always contains just the parameter you think it exist

Again please understand this example

In the db there are json like this

{
    UserID: "TT",
    Name: "ABC",
    CustomData:"123",
}

Whenever you do ANYTHING that parse this json into static type in C#. You will lose the data you don't know about. And when you pass that object to another system. You destroy the data we load from DB

I see you all never get my point why I request dynamic intellisense. Please understand the problem first

[Thaina]

To put it simply

In most NoSQL database we use today let we save document in json format

It require us to work with json object by loading whole document out from DB. Modified some field, and save it back by posting whole document back to database

But whenever you load any json object into static type. Any field that named difference from what you have will gone missing

The best way to handle this situation is using dictionary and wrap it as dynamic object. That what we use in almost all of json plugin. NewtonSoft is one popular example

But whenever that object is large. Most of the time it has some field that it always have. If it is data of user it always have id and name for example. And salsa typescript is the best solution to deal with this scenario. Please go use it once and you will understand

@eyalsk As I said. Please go use typescript or js salsa with nosql db and you will understand. you still trying to mess with this issue without understanding and that is what frustrate me. I cannot appreciate your intervention because you never ever try to understand the problem

dynamic object can change. But we always have something in mind that it would not or should not change even if it is dynamic object

We want it to be dynamic because it has something that can change. But something is not everything. We may want it to have 100 fields that could change but only 10 field that will be present or null. And that's all we need to deal with dynamic object in the world

[DustinCampbell]

@Thaina: I do understand the scenario you're talking about, which is why I've asked for more detail. I've spent a lot of time thinking about IntelliSense for dynamic in the past.

To implement dynamic IntelliSense reliably (for some definition of "reliable" :smile:), you must either use the runtime type of an object (which isn't possible to determine statically) or add features to the type system (a la TypeScript) to allow hints to be provided about what a type might be.

The proposal you're making is similar to the latter approach: adding hints via attributes. The problem is that the examples you've shown are a little too simplistic and confusing. Consider your own example:

```C#
[Dynamic(typeof(IEnumerable>))]
dynamic keyValuePairs = new Dictionary();
keyValuePair.FirstOrDefault().Va // show intellisense for value as float

First, the use of an attribute limits the feature so that it this will only work if `keyValuePairs` is a field (since attributes can't be attached to locals).

Second, the example falls apart as soon as it is passed to another method.

```C#
[Dynamic(typeof(IEnumerable<KeyValuePair<string,float>>))]
dynamic keyValuePairs = new Dictionary<string,float>();

void M2()
{
    M1(keyValuePairs);
}

void M1(dynamic d)
{
    d.FirstOrDefault().Va // show intellisense for value as float
}

You could achieve this, but it would take a significant amount of work to perform the flow analysis necessary to determine the type hint for d.

[Thaina]

@DustinCampbell What I request from the start is exactly latter case, as I mention JSDoc of typescript

I don't think we could be ever to reliably generate intellisense on the fly. Instead, as programmer, I just want to control what it will be present to me by myself

The ability to control what to hint is all I need. In fact I think that's all we should need. To let compiler guess your dynamic is too lazy

But you right, sorry I just forget that attribute cannot put on local variable. So it must be comment or some other mechanism. But the point is just to add custom hint into the code for dynamic object. I just use attribute because it feel familiar

Also its fine that it cannot work out of its scope. For any new things came in scope you should and must apply attribute mark it. using typescript salsa is also like that

```C#
[Dynamic(typeof(IEnumerable>))]
dynamic keyValuePairs = new Dictionary();

void M2()
{
M1(keyValuePairs);
}

void M1([Dynamic(typeof(IEnumerable>))]dynamic d)
{
d.FirstOrDefault().Va // show intellisense for value as float
}

or to make this possible with local var


```C#
/// <var type="IEnumerable<KeyValuePair<string,float>>" />
dynamic keyValuePairs = new Dictionary<string,float>();

void M2()
{
    M1(keyValuePairs);
}

/// <param name="d" type="IEnumerable<KeyValuePair<string,float>>" />
void M1(dynamic d)
{
    /// <var type="IEnumerable<KeyValuePair<string,float>>" />
    dynamic dict = new Dict();
    d.FirstOrDefault().Va // show intellisense for value as float
}

[DustinCampbell]

To my eye, the annotations are already getting a bit out of control. I can see this appealing to a certain sort of developer, but it's probably not something that would necessarily appeal to everybody. As I mentioned, you can definitely do this if you want to invest the time and are OK with the limitations.

We've considered allowing custom CompletionProviders to be included in a NuGet package in the same way that a Roslyn analyzer can be today. To me, that would be the ideal way to deliver a feature like this. That way, a user could simply reference the NuGet package for a particular project where they want to use this enhanced completion behavior.

@Pilchie, what do you think?

[Thaina]

@DustinCampbell If I know the proper place to do I could start with it. But it seem there are so much dependency and roslyn are too rigid to extend

If I start modify roslyn myself I could not use it until later months or years it got pull into so I want to request it

That's why I ask you can I just make it work on omnisharp-roslyn or omnisharp-vscode? Is all the required data can be acquired from omnisharp or we need to extend roslyn to provide it?

[DustinCampbell]

@Thaina: I've already answered this question:

It would be more work to do this in omnisharp-vscode. Because omnisharp-vscode is written in TypeScript and runs on nodejs, you wouldn't be able to write this in C#, or use Roslyn or other managed libraries without other shenanigans. Adding it to omnisharp-roslyn would be the way to go.

[Thaina]

@DustinCampbell But I am quite sure that certain sort of developer is everyone who work with nosql database. Or server side for javascript client

[Thaina]

@DustinCampbell I have seen that answer it but I don't quite sure that omnisharp-vscode can request all datas required for this feature from roslyn

The question is actually to ask "do I need to do anything with roslyn for this feature, or I can go with omnisharp alone"

If it latter then I would try to make it myself

[DustinCampbell]

@DustinCampbell But I am quite sure that certain sort of developer is everyone who work with nosql database. Or server side for javascript client

I disagree with that point. I believe that the class of developers that you describe above are definitely interested in having IntelliSense support for dynamic. However, I don't think all of them want to have annotations littered throughout their code to achieve it. I expect many of them would like IntelliSense just work without any annotations.

@DustinCampbell I have seen that answer it but I don't quite sure that omnisharp-vscode can request all datas required for this feature from roslyn

I think you're just misunderstanding the architecture slightly. omnisharp-vscode doesn't talk to roslyn. It looks more like this:

• omnisharp-vscode is written in TypeScript and talks to omnisharp-roslyn via a simple protocol.
• omnisharp-roslyn uses Roslyn to process C# code.

So, omnisharp-roslyn is where you'd want to implement this feature. I can't guarantee that the OmniSharp community would embrace the feature however.

[DustinCampbell]

Many things are possible but if you add types through comments then why not just replace the dynamic object with an actual type?

From the start this is the proof that you don't understand the problem

Please keep things civil here @Thaina

[DustinCampbell]

@DustinCampbell I'm really baffled what scenarios this solve when proxies can be used to provide the same thing?

I mean this seems like having type definitions for JavaScript objects... something that can be doable today with C# through proxies.

Can you enlighten me?

From what I can tell, the idea is to keep the "dynamicness" of "dynamic" without having to constantly reinterpret through the lens of some a static type, which has its own downsides. However, tooling support is still desirable and that's what @Thaina is hoping to achieve. I'm not sold on the particular proposal of using annotations, but I don't have to be sold on the proposal. @Thaina is free to build it if he thinks it will be valuable.

[Thaina]

@DustinCampbell

I don't think all of them want to have annotations littered throughout their code to achieve it

I think they would still appreciate that this is better than nothing. Well, this is not the ideal solution, but I don't think the ideal solution would be able to implement less than 4 years at least. If it the same feature as typescript we could start working with any project right now

I think salsa is widely used enough to make a comparison that, many people can tolerate annotations if it needed for intellisense of unknown

Also I think if it is xml documentation, it's mean we just add a little more things into xml documentation

I think you're just misunderstanding the architecture slightly. omnisharp-vscode doesn't talk to roslyn. It looks more like this:

Sorry to make you misunderstand. What I really mean there is omnisharp-roslyn. I know how the architecture work that omnisharp-roslyn talk to roslyn

But my point is, is all the required data was provided from roslyn and omnisharp-roslyn can use it to build this feature?

I once proposed the feature in omnisharp about sorting completion items based on type hierarchy (like MonoDevelop doing) and it seem omnisharp cannot do it because roslyn don't provide a type data along with completion item, so it cannot be done without modifying roslyn

So I just want to ask that will it might have the same problem. Is roslyn already capable and I just need to modified omnisharp. Or I need to wait for some change in roslyn anyway?

[DustinCampbell]

But my point is, is all the required data was provided from roslyn and omnisharp-roslyn can use it to build this feature?

Yes, all of the information is there. Within omnisharp-roslyn, you have access to all of Roslyn and there is sufficient information provided by Roslyn to do this.

I once proposed the feature in omnisharp about sorting completion items based on type hierarchy (like MonoDevelop doing) and it seem omnisharp cannot do it because roslyn don't provide a type data along with completion item, so it cannot be done without modifying roslyn

I'm not sure why OmniSharp said this couldn't be done. It certainly can. :smile:

So I just want to ask that will it might have the same problem. Is roslyn already capable and I just need to modified omnisharp. Or I need to what for some change in roslyn anyway?

Roslyn is capable. It may not be a small amount of work, but the data is there.

[Thaina]

@DustinCampbell Thank you very much for your precious explanation

[DustinCampbell]

I'd also like to reiterate that there is no guarantee that omnisharp-roslyn will embrace this feature. Also, as the owner of the experience for C# in VS Code, I'm not quite comfortable with it either, at least not on by default. I have a goal of keeping the editing experience in VS Code and VS in sync. That said, if the feature goes into omnisharp-roslyn, it could easily be configurable under an option.

[DustinCampbell]

@eyalsk No you never ever understand. You also go to mock me on the thread that I have a problem with doing proxy. And now you not even remember that I am already doing proxy so I know the proxy is and I request this feature because it is not a good enough solution

You always attack most of my idea and you still thinking you help me
You intend to do it or not is not my concern but
YOU REALLY MESS WITH MY IDEA THREAD WITHOUT HELPING ANYTHING BETTER

And that's because YOU NEVER EVER TRY TO UNDERSTAND THE PROBLEM

Let's drop this, OK? These are simply different approaches to dealing with dynamic in a statically-typed language. Arguing about this is really not appropriate.

[DustinCampbell]

I'm not concerned who started the dispute, but I would like it to end. https://opensource.microsoft.com/codeofconduct/

[eyalsk]

@Thaina It's okay, I will unsubscribe from all your discussions and won't join any of them in the future.

Have a nice day.

[Thaina]

@eyalsk Wow. After my threads became uncleanable mess you still think I can have a nice day with?
I should ask you are you feel good now?

Good day sir

[svick]

If what you want is to have something that is dynamic, but also has some static type information, then proposals that suggest exactly that might be of interest: https://github.com/dotnet/roslyn/issues/3012 and https://github.com/dotnet/roslyn/issues/5306.

[Thaina]

@svick Thank you recommending that for I can subscribed to it

But it seem those thread has no movement so long. And I think it overkill to add language feature just for intellisense. All we need for dynamic is intellisense so it should not be syntax to compiled

If we need to extend compiler to support new syntax would it be harder to implement?
That being said, I like those syntax too if it possible to implement

[kzu]

So, to chime in super late @DustinCampbell, regarding your comment on allowing completion providers via nugets, is that something we support already? /cc @Pilchie

Thanks!

[Pilchie]

• @jinujoseph for completion.

[dpoeschl]

@kzu No, that ability does not exist today. The only way to do this currently is the mechanisms Dustin described earlier (VS: export as [ExportCompletionProvider]; Omnisharp: more complicated as Dustin explained although maybe that's changed and I'm unaware).

I don't see an active issue for this... If this is something you think you'd make use of, please file an issue for it in this repo. Thanks!

[kzu]

Done, thanks! https://github.com/dotnet/roslyn/issues/30270

[VBAndCs]

So, what is the status of this now?

[CyrusNajmabadi]

@VBAndCs please stop pinging issues asking for status. If there has been no movement, then there as been no movement. If you would like to contribute toward improvements here reach out and let us know. We can let you know if we'd take PR contributions.

[jmarolf]

My understanding of this thread is that we would like to do something to make intellisense for dynamic work in more places than it does today. It is unclear what the correct design for that feature would be though as attributes has several drawbacks. No clear design for this feature would be one of the main reasons the status has not changed.

[CyrusNajmabadi]

Note: i'm going to close this out. There is an existing mechanism to support this scenario. Namly, the public CompletionProvider api.

With that people can build completion that htey want for advanced scenarios like this. Specifically, the thread has stated numerous times that supporting something like a jsdoc approach like salsa from typescript would be sufficient.

Such an approach could absolutely be built externally using our public api using whatever mechanism the author deems fit. i.e. they could use attributes on data for this, or they could add special sigils in doc comments or regular comments to indicate this information.

I do not see anything additional that roslyn has to add here.

[CyrusNajmabadi]

Marking as fixed as we now have a public, 100% supported mechanism for 3rd parties to enhance completion lists with this sort of information.

[VBAndCs]

@CyrusNajmabadi

please stop pinging issues asking for status

You sure?

Marking as fixed

No need for an apology :)