ILSpy assembly reference missing

Question

I have a project "A", which references 2 other projects "B" and "C".

For both references actual functions from these project are used in "A".
But when I open the assembly A.dll with ILSpy, it only shows "B" and not "C" under references.
If I remove the reference that is missing, my project no longer compiles, so it is in fact actually used.

What could be the reason for this?

Answer 1

The .dll will only contain an assembly reference if it uses types from the referenced assembly. At compile-time it's possible that you need some additional assemblies.

Example:

C.dll:

class C { public void M1() {} }

B.dll:

class B : C { public void M2() {} }

A.dll:

class A {
   public static void Main() {
       new B().M2();
   }
}

When building A.dll, the compiler will require both B.dll and C.dll so that it can list all methods in type B. However the resulting IL code will only reference class B and method B.M2, so the compiler does not need to emit an assembly reference to C.dll.