v2: Make it easier to model OpenAPI tags as a hash set

[captainsafia]

The OpenAPI specification states that:

Each tag name in the list MUST be unique.

To reflect this attribute, it would be great if we could model the top-level tags collection in to the document as a hash set of sorts. However, because it is currently modeled as an IList it is difficult to encode this uniqueness constraint in the source:

OpenAPI.NET/src/Microsoft.OpenApi/Models/OpenApiDocument.cs

Line 74 in 47bf1eb

public IList<OpenApiTag>? Tags { get; set; } = new List<OpenApiTag>();

We should consider taking a breaking change to change the type to ICollectionor IEnumerable so that consumer can initialize a HashSet to enforce the uniqueness constraint.

[captainsafia]

I should also add that this will require some sort of comparer implementation for OpenApiTag type. Here's one that we implement currently in ASP.NET Core.

https://github.com/dotnet/aspnetcore/blob/f42307ccd08ee02c885de9427acaf3c8f37fc377/src/OpenApi/src/Comparers/OpenApiTagComparer.cs

[baywet]

@captainsafia thanks for surfacing this up! I put together #2167 which does a couple of things:

1. document tags are a HashSet, enforcing uniqueness
2. operation tag references are a HashSet, enforcing uniqueness
3. document tags are not assigned by default, saving collection initialization if tags are not used
4. operation tag references are not assigned by default, saving collection initialization if tags are not used

I suspect this last point is going to reduce the memory footprint of the library for large descriptions without tags.

Let us know what you think!

[captainsafia]

@baywet Thanks for taking this feedback into consideration! I took a look at the PR and it more or less aligns with what the ASP.NET Core implementation is currently doing.

Once this goes out in a preview, I'll try picking it up and seeing if I spot any issues with it in practice.

[baywet]

This has been released with #2170 However it seems that nuget still has not processed our release. We're working with them to understand why.