Add union link connection type support

[huchenlei]

Requested by @Kosinkadink

Supports running workflow with union types, i.e. types separated with comma like T1,T2,.... The frontend code (litegraph) already supports the connection of it. It's the backend validation failing blocking this feature to be properly used.

Before:

After:

Reproduction workflow

UnionTest.json

Required custom nodes:

• https://github.com/Comfy-Org/ComfyUI_devtools
• https://github.com/WASasquatch/was-node-suite-comfyui

[Kosinkadink]

Did some testing by making an AnimateDiff-Evolved input accept 4 different inputs, and it works as expected when running:

One thing that these union type inputs can't do (for good reason) is take primitive node inputs. This means that there is no way to connect basic types like INT, FLOAT, STRING etc to them with vanilla ComfyUI nodes. This is outside the scope of this PR, but I think it's finally time for ComfyUI to have native nodes for what the primitive node tries to do. A bunch of custom node packs have their own nodes to do this, but this should not require any node packs to solve or deal with. Primitive nodes also don't show their previous value when disconnected, so they are just messy to work with for the most part.

[huchenlei]

Did some testing by making an AnimateDiff-Evolved input accept 4 different inputs, and it works as expected when running:

One thing that these union type inputs can't do (for good reason) is take primitive node inputs. This means that there is no way to connect basic types like INT, FLOAT, STRING etc to them with vanilla ComfyUI nodes. This is outside the scope of this PR, but I think it's finally time for ComfyUI to have native nodes for what the primitive node tries to do. A bunch of custom node packs have their own nodes to do this, but this should not require any node packs to solve or deal with. Primitive nodes also don't show their previous value when disconnected, so they are just messy to work with for the most part.

Primitive node support requires changes in the frontend, as it has custom logic on type checking.

[Amorano]

Requested by @Kosinkadink

Supports running workflow with union types, i.e. types separated with comma like T1,T2,.... The frontend code (litegraph) already supports the connection of it. It's the backend validation failing blocking this feature to be properly used.

Thank you for adding this back in -- been waiting for months for this to regress =D