Autodesk: Build with zlib static library

[erikaharrison-adsk]

Description of Change(s)

We need to be able to support using a static zlib library. This change provides that.

Fixes Issue(s)

• N/A

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9779

[jesschimein]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[dgovil]

A related issue is that we only need Zlib to build on Windows. Does this affect your PR at all? #2988

[yangel2017]

Yes, #2988 will affect my PR. Using static zlib need to build zlib from the source but not from the system installed one. If #2988 merges first, my PR needs to update.

[dgovil]

Would you only need to support static builds on Windows? Or would you need to support them on Linux and Mac too, where the OS vends it?

[yangel2017]

We would like to support static builds on Windows, Mac and Linux.

[dgovil]

Okay. Just a few more questions:

1.If I understand the change correctly, this would make it always statically linked. I think many of us would still prefer to use dynamic linking, especially on platforms where the OS provides it.

2. Zlib is used by multiple dependencies, that all default to being dynamically linked in. Wouldn't this PR cause each of them to statically link Zlib, resulting in multiple runtime copies of it?

3. I presume you also bundle those dependencies into your products.
   Would it be better for you to link against the version of each dependency in your product instead, rather than having USD build them again for you?

[yangel2017]

We propose this because when an application uses usd with dynamic zlib library of version A, and the application itself also dynamic links zlib libraries with version B, if version A and B are not compatible then the problem occurs. Use static libraries can avoid the problem. But it indeed may result in multiple runtime copies of it.

[dgovil]

I think this would need to be an option perhaps? I don't agree with the approach of making this a default as I think being dynamically provided by the OS is the more preferable option for a wider range of uses.

[asluk]

I agree that it needs to be optional 🙏🏼