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

[Paul Sandoz]

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);
        }
    }
}