[foreign-jextract] Bindings to functions declared in header file

[Maurizio Cimadamore]

That's the expected behavior. We need to polish it a bit so that a 
better exception is generated.

Another thing which clients might do, using the API, could be to filter 
out bindings not available (by looking at the library statically, at 
extraction time).

We used to have such a filtering capability, but we have removed it 
since we switched to the more minimalistic jextract.

Maurizio

On 07/08/2020 18:47, Paul Sandoz wrote:
> Hi,
>
> The jextract tool generates bindings to functions declared in a header file.
>
> MethodHandle lookup will return null, since the function does not exist in the corresponding shared library.
>
> $ jshell --class-path . --add-modules jdk.incubator.foreign -R-Dforeign.restricted=permit -R-Djava.library.path=.
> |  Welcome to JShell -- Version 16-internal
> |  For an introduction type: /help intro
>
> jshell> import a.a_h
>
> jshell> a_h.f_in_source()
>
> jshell> a_h.f_in_header()
> |  Exception java.lang.AssertionError: java.lang.NullPointerException: Cannot invoke "java.lang.invoke.MethodHandle.invokeExact(Object[])" because the return value of "a.a_h$constants.f_in_header$MH()" is null
> |        at a_h.f_in_header (a_h.java:30)
> |        at (#3:1)
> |  Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.invoke.MethodHandle.invokeExact(Object[])" because the return value of "a.a_h$constants.f_in_header$MH()" is null
> |        at a_h.f_in_header (a_h.java:28)
> |        …
>
>
> More details below.
>
> Paul.
>
>
> $ more a.h
> void f_in_source();
>
> static void f_in_header() {
> }
>
>
> $ more a.c
> #include "a.h"
>
> void f_in_source() {
> }
>
>
> $ more a/a_h.java
> // Generated by jextract
>
> package a;
>
> import java.lang.invoke.MethodHandle;
> import java.lang.invoke.VarHandle;
> import jdk.incubator.foreign.*;
> import jdk.incubator.foreign.MemoryLayout.PathElement;
> import static jdk.incubator.foreign.CSupport.SysV.*;
> public final class a_h {
>
>      private a_h() {}
>      public static MethodHandle f_in_source$MH() {
>          return a_h$constants.f_in_source$MH();
>      }
>      public static void f_in_source (Object... x0) {
>          try {
>              a_h$constants.f_in_source$MH().invokeExact(x0);
>          } catch (Throwable ex) {
>              throw new AssertionError(ex);
>          }
>      }
>      public static MethodHandle f_in_header$MH() {
>          return a_h$constants.f_in_header$MH();
>      }
>      public static void f_in_header (Object... x0) {
>          try {
>              a_h$constants.f_in_header$MH().invokeExact(x0);
>          } catch (Throwable ex) {
>              throw new AssertionError(ex);
>          }
>      }
> }
>