How Does .NET Resolve Dependencies When a netstandard2.0 Library References a net8.0 Library?

[amitsharma7960]

I have the following class libraries in my application:

Library A: targets both netstandard2.0 and net8.0
Library B: targets netstandard2.0 and references Library A
Executable project: targets net8.0 and references Library B

I expected the netstandard2.0 version of Library A to be restored (since Library B targets only netstandard2.0), but instead, the net8.0 version of Library A is restored. It appears that because the entry point (the executable) targets net8.0, all dependencies are resolved for net8.0, even if they are not direct dependencies of the executable.

Despite this, the application runs fine at runtime with no errors so far.

My question:
How does this configuration work at runtime? Specifically, how can a netstandard2.0 library (Library B) reference a net8.0 library (Library A) without causing compatibility issues? I was under the impression that a netstandard2.0 library could not reference a net8.0 library.

Any insights into how .NET resolves these dependencies and why this works would be greatly appreciated!
@davidfowl, would you be able to shed some light on this?

[huoyaoyuan]

It appears that because the entry point (the executable) targets net8.0, all dependencies are resolved for net8.0, even if they are not direct dependencies of the executable.

Yes, all dependencies used at runtime are picked by the executable, not transitive dependencies.

How does this configuration work at runtime?

Target frameworks don't exist in the view of CLR. They are resolved at SDK and NuGet level only.

Specifically, how can a netstandard2.0 library (Library B) reference a net8.0 library (Library A) without causing compatibility issues? I was under the impression that a netstandard2.0 library could not reference a net8.0 library.

It always references B(netstandard2.0). It's just B(net8.0) being able to satisfy the reference.

In .NET, the referenced assembly used at compile time and the runtime assembly used at runtime are very different. When a library was compiled for net6.0, it needs to reference net6.0 version of the BCL. Then at runtime, net8.0 version of BCL will be used to satisfy the dependency.

[amitsharma7960]

Thanks for your reply!

It always references B(netstandard2.0). It's just B(net8.0) being able to satisfy the reference.

I understand that the executable always references B(netstandard2.0) and in the output folder, the same is also available.
However, the thing that is confusing me is that the output folder contains the A(net8.0). Since B references A, how this works at runtime?

[huoyaoyuan]

Well it's a typo about library name.

B(netstandard2.0) references A(netstandard2.0), and A(net8.0) is provided. It simply satisfy the reference to A(netstandard2.0). Just like how BCL(net8.0) satisfies reference to BCL(net6.0). Target framework is not a part of assembly identity.

[amitsharma7960]

I think the explanation given by @huoyaoyuan makes sense. Thank you!