Re: AM_PROG_GCJ fails at `make' if nothing else defines OBJEXT

[Jack Kelly]

On Sun, Jun 7, 2009 at 4:06 PM, Ralf Wildenhues<address@hidden> wrote:
>> 2. The suffix mechanism might not be quite enough for Java projects
>> with native methods using the C++ interface.
>
> I'm sorry, but I fail to parse this.  Even with the example you gave, it
> is unclear to me.  Can you rephrase this, state the problem setup in
> more detail, and which parts are not supported by Automake?  Can these
> parts easily be worked around by the Makefile.am author?

This is the best I can come up with:

configure.ac:
8<---
AC_INIT([a], [b], [c])
AM_INIT_AUTOMAKE([foreign])
AC_PROG_CXX
AM_PROG_GCJ
AC_PATH_PROG([GCJH], [gcjh], [no])
AS_IF([test "$GCJH" = no], [AC_MSG_ERROR([bad luck.])])
AC_CONFIG_FILES([Makefile])
AC_OUTPUT
8<---

Makefile.am:
8<---
noinst_PROGRAMS = cnitest

BUILT_SOURCES = CniTest.h
cnitest_SOURCES = CniTest.java CniTest_native.cc
cnitest_LDFLAGS = --main=CniTest

.java.class:
        $(GCJ) -C $<
# The -cp is to work around a bug in ubuntu's gcjh setting the
# classpath wrong.
.class.h:
        $(GCJH) -cp .:/usr/share/java/libgcj.jar $<
8<---

CniTest.java:
8<---
public class CniTest {
    public static native void printFromCxx(String message);
    public static void main(String[] args) {
        printFromCxx("Hi from C++");
    }
}
8<---

CniTest_native.cc:
8<---
#include <java/io/PrintStream.h>
#include <java/lang/System.h>
#include "CniTest.h"

void CniTest::printFromCxx(::java::lang::String * arg) {
  java::lang::System::out->println(arg);
}
8<---

> What files does this generate in general, can we tell in some way,
> ideally, without looking at the .java files?  (If we'd have to look
> at them, then in principle, the Makefile file (or Makefile.in) would
> depend upon the .java file, which seems ugly.)

This has the usual problems with compiling java: multiple outputs from
the one input. (see the _JAVA primary.)

In fact: would it be possible to add GCJ support to the _JAVA primary?
I'm not a java expert, but I'm reasonably sure that every .java file
has either a public class or interface, so adding a rule to
Makefile.in of the form:
CniTest.class: classdir.stamp
might work. Generate one such rule for each java file in a _JAVA
primary and add them to .PHONY.

This then simplifies the Makefile.am, so the explicit .java.class rule
can go away and be replaced with a noinst_JAVA = CniTest.java entry.
The .class.h rule can then be moved into a fragment.

An autoconf test would also be needed to find and AC_SUBST a value for
JAVAC and JAVACFLAGS, and use $(GCJ) -C as one of the options.
(AM_PROG_JAVAC?)

Does this make sense?

-- Jack