Extension members not suggested by IntelliSense when "Show items from unimported namespaces" is enabled

[meziantou]

Version Used:

• .NET SDK 10 RC1
• 5.0.0-2.25459.9 (5d47bb1)
• Language version: 14.0

Steps to Reproduce:

You can surely create your own extension member (using the new extension keyword), but here's my repro:

1. Create a new application
2. Add a reference to Meziantou.Framework@5.0.0
3. Ensure "Show items from unimported namespaces" is enabled in Visual Studio options

Extension source code: https://github.com/meziantou/Meziantou.Framework/blob/84a3684af409a323159229914ed7d1c8f54dd596/src/Meziantou.Framework/EncodingExtensions.cs

• Extension methods show up (using the "old" syntax):

• Extension members are not visible (using the new extension syntax)

• Extension members show up after adding the using directive

Expected Behavior:

• Extension members should appear in IntelliSense automatically, just like extension methods using the old syntax

Actual Behavior:

• Extension members do not appear unless a using directive is explicitly added
• Extension methods (old syntax) appear correctly in completion

[phil-allen-msft]

It seems like one of: The IDE isn't asking a question that could return Extension properties, the IDE is filtering out returned Extension properties, or the Compiler isn't returning extension properties for a question that reasonably should.

[jcouv]

It looks like work is needed in the IDE in ExtensionMethodImportCompletionHelper but that is blocked on adding a new compiler API (tracked by #80273).

Relates to test plan #76130

[jcouv]

The needed compiler API is being added in #80659
I took a quick look at IDE layer, but it was more complicated than I'm prepared to handle at this time. So I'll leave it up to the experts