RFR: 8238226: Revisit FunctionDescriptor

[Jorn Vernee]

Continuation of: https://mail.openjdk.java.net/pipermail/panama-dev/2020-February/007418.html

> Hi,
> 
> Please review the following patch that revisits FunctionDescriptor: 1. 
> Adds appendArgumentLayouts, and changeReturnLayout combinator methods. 
> 2. Removes the variadic flag. This flag was not really being used in 
> practice, since we can not link variadic functions directly any ways. 
> Using the new appendArgumentLayouts method we can 'specialize' a base FD 
> with different argument layouts representing vararg arguments. I think 
> if a similar flag is needed in the future, we should consider adding 
> annotations to FunctionDescriptor, and making it an annotation instead, 
> but currently it doesn't seem like it's pulling it's weight by being in 
> the API.
> 
> Webrev: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/cleanup_fd/webrev.00/
> Bugs: https://bugs.openjdk.java.net/browse/JDK-8238226, 
> https://bugs.openjdk.java.net/browse/JDK-8237580
> 
> Again, this patch applies on top of the Binding cleanup patch.
> 
> Thanks,
> Jorn

-------------

Commits:
 - a986883a: Add FunctionDescriptor combinators & remove varargs

Changes: https://git.openjdk.java.net/panama-foreign/pull/15/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/15/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238226
  Stats: 170 lines in 16 files changed: 22 ins; 68 del; 80 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/15.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/15/head:pull/15

PR: https://git.openjdk.java.net/panama-foreign/pull/15