`CS7003` is only reported during build and doesn't appear on the IDE

[Rekkonnect]

Version Used:
Visual Studio 2026 (18.0.0 Insiders [11012.119])
Roslyn 5.0.0-2.25459.9 @ 5d47bb1

Details:

The error CS7003 "Unexpected use of an unbound generic name" is not reported before the project is built, and the IDE will not display the error squiggles

Example:

https://sharplab.io/#v2:CYLg1APgAgzABFATHAwgWAFAG9Nz3ABwCcBLANwEMAXAUwQEYA2OYATwDsKBbEgYzgAiHbnwCyNKgAsA9sAAUbTj34l2BAK5UAlLnw4M+QwgDscVRqoA6AMrSuEyaoDmAHgB8crQG16AXQDcungAvkFwYbAMzFD0AAxwtvZSzp5h+kb4UKYxsZYAolwEVKyBBvihGBVAA===

public class C
{
    private static dynamic DynamicMethod(dynamic input)
    {
        return input.Something<>()[1];
    }
    
    public static string Something()
    {
        return string.Empty;
    }
}

Screenshot

Expected Behavior:
The error is reported and shown with squiggles in the IDE like every other error

Actual Behavior:
The diagnostic is only emitted during build and is not visible in the IDE

[CyrusNajmabadi]

I've debugged through this, and IDE is just calling into compiler, which is not returning any diagnostics here. Compiler will need to look at this. @jaredpar for retriage.

[jaredpar]

@jjonescz for retriage