[foreign-abi] RFR: Rename SystemABI to ForeignLinker, and move C support to a separate class.

[Maurizio Cimadamore]

On Mon, 18 May 2020 10:39:38 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Hi,
> 
> This patch renames SystemABI to ForeignLinker, and moves the C support, namely layout constants and the getSystemABI
> factory, to a new class named `C`.
> This is an effort to untangle the otherwise ABI/Language agnostic API of SystemABI from APIs that serve C specifically.
> 
> The rename from SystemABI to ForeignLinker attempts to make it clear that there is not a single ABI per system, but
> there can be multiple. Although the same holds for C, in practice there is one de facto ABI per system, so we still
> keep the getSystemLinker (renamed from getSystemABI) factory for C.  The new name also better reflects what the class
> does; it links a native function as a MethodHandle, or links a Java function as a native function pointer. The overall
> theme being linking.  I've also removed some of the ABI name constants that were in SystemABI previously, as they were
> unused.
> (FYI, the name change in the diff on GitHub from SystemABI -> C seems to have been inferred automatically, and is
> incorrect. The actual rename is from SystemABI -> ForeignLinker, and the C class was added separately).
> Thanks,
> Jorn

Looks good - there are few things that need more thinking:
* the name `C` seems thin. It doesn't describe very well what the class is for. Maybe `CSupport` or something like that
  might be more expressive
* if we have already C somewhere in the class name, there's a question as to whether constants should drop their C-ness
  (e.g. `C.C_BOOL` looks odd).
* I wonder if, now that we have a dedicated C class, helpers functions to read/write strings shouldn't just go in there
  (e.g. take Cstring and expand its static helpers onto the new class).

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PR: https://git.openjdk.java.net/panama-foreign/pull/174