ABI stability, symbol versioning, and as-appropriate SONAME updates

[stewartsmith]

Describe the feature

aws-c-cal/CMakeLists.txt

Line 156 in b7b7402

# Our ABI is not yet stable

indicates that aws-c-cal is not yet ABI stable.

This request is for one (or both) of the following to be done:

1. Appropriate SONAME updates when there are ABI changes (preferably limiting changes)
2. A rather stable ABI and API so that consumers do not need to change very often.

We have a strong preference for shared libraries to use symbol versioning as this majorly helps in backwards and forwards compatibility across library and application versions.

Use Case

Being able to package software that uses aws-c-cal as a dependency to be included in Amazon Linux and other Linux distributions.

In order to be packaged for Linux distributions such as Amazon Linux, applications should use shared libraries, and not statically link their dependencies, especially if there are multiple applications with the same dependency.

https://github.com/awslabs/mountpoint-s3/ is one example of a package that has an aws-c-cal dependency that should be dynamically linked rather than statically, and a request for it to be packaged is fairly popular, see awslabs/mountpoint-s3#442

Proposed Solution

Immediate ask: aws-c-cal project adds ABI compatibility testing, and changes the SONAME of the shared library as needed.

Preferred solution: a decently stable ABI with a library using symbol versioning in order to enhance forwards and backwards compatibility.

This ask would include the dependencies of aws-c-cal as well.

Other Information

This is as much policy as it is any technical work. I can very much send PRs that enable some ABI compatibility checking and enabling symbol versioning, but setting the policy of the project to care about ABI compatibility is not something I can directly do, and must come from maintainers.

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change