Missing class path under MacOS for Java FFI

[drever]

Description

I'm trying to get the FFI to Java running on MacOS 10.14.3, using the documentation here. The class eta.first.Utils is not found.

Expected Behavior

The java function should be called from eta.

Actual Behavior

Exception in thread "main" java.lang.NoClassDefFoundError: eta/first/Utils
at main.Main.main1(Main.hs:10)
at main.Main$main1.applyV(Main.hs)
at eta.runtime.exception.Exception.catch_(Exception.java:132)
at main.Main.main3(Main.hs)
at main.Main.DZCmain(Main.hs:10)
at main.Main$DZCmain.applyV(Main.hs:10)
at eta.runtime.stg.Closures$EvalLazyIO.enter(Closures.java:154)
at eta.runtime.stg.Capability.schedule(Capability.java:254)
at eta.runtime.stg.Capability.scheduleClosure(Capability.java:210)
at eta.runtime.Runtime.evalLazyIO(Runtime.java:397)
at eta.runtime.Runtime.main(Runtime.java:390)
at eta.main.main(Unknown Source)
Caused by: java.lang.ClassNotFoundException: eta.first.Utils
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
... 12 more

Possible Fix

The bash file dist/build/eta-0.8.6.4/test-0.1.0.0/x/test/build/test/test starts the jvm with the corresponding class path. Adding the path to the class files manually fixes the problem.

Steps to Reproduce

• Install eta on MacOS with etlas
• Implement java FFI according to documentation.
• etlas run

Your Environment

• Did you install an older version of Eta/Etlas before?
  First installation
• Current Eta & Etlas version:
  etlas version 1.5.0.0
• Operating System and version:
  MacOS 10.14.3

[jneira]

Hi, could you share your .cabal config? the content should be something like:

name:                eta-first
version:             0.1.0.0
license:             BSD3
license-file:        LICENSE
author:              [your name]
maintainer:          [your email]
build-type:          Simple
extra-source-files:  ChangeLog.md
cabal-version:       >=1.10

executable eta-first
  main-is:             Main.hs
  other-modules:       Primes
  build-depends:       base >=4.8 && <4.9
  hs-source-dirs:      src
  java-sources:        java/eta/first/Utils.java
  default-language:    Haskell2010

And the tree:

eta-first
  -src
    -Main.hs
  -java
    -eta
      -first   
        -Utils.java
  -eta-first.cabal
  -Setup.hs

For the path of the bash file it seems you named your executable test and if all would be correct the class should be already inside dist/build/eta-0.8.6.4/test-0.1.0.0/x/test/build/test/test.jar

[drever]

Sure, the cabal file:

-- Initial test.cabal generated by etlas init.  For further documentation, 
-- see http://eta-lang.org/docs/

name:                test
version:             0.1.0.0
-- synopsis:            
-- description:         
license:             BSD3
license-file:        LICENSE
author:              Johannes Drever
maintainer:          
-- copyright:           
-- category:            
build-type:          Simple
extra-source-files:  ChangeLog.md
cabal-version:       >=1.10

executable test
  main-is:             Main.hs
  other-modules:       Primes Counter
  java-sources:        java/Counter.java
                     , java/Utils.java
  build-depends:       base >=4.11 && <4.12
  hs-source-dirs:      src
  default-language:    Haskell2010

And the tree:

.
├── ChangeLog.md
├── LICENSE
├── Setup.hs
├── java
│   ├── Counter.java
│   └── Utils.java
├── src
│   ├── Counter.hs
│   ├── Main.hs
│   └── Primes.hs
└── test.cabal

The executable is named test and there is a file dist/build/eta-0.8.6.4/test-0.1.0.0/x/test/build/test/test.jar. The problem seems to be that the startup script does not set the class path correctly. When I paste it manually it works as expected.

Thanks for helping!
Johannes

[jneira]

The cabal file and the tree seems to be correct.

In theory the script should not add the class file to classpath, it should be inside dist/build/eta-0.8.6.4/test-0.1.0.0/x/test/build/test/test.jar.
Could you inspect the content of dist/build/eta-0.8.6.4/test-0.1.0.0/x/test/build/test/test.jarto check if eta/first/Utils.class is in it?

In my windows env i've tested it succesfully and my jar contents are:

C:\ws\eta\eta-first\dist\build\eta-0.8.6.4\eta-first-0.1.0.0\x\test\build\test>mkdir jar

C:\ws\eta\eta-first\dist\build\eta-0.8.6.4\eta-first-0.1.0.0\x\test\build\test>copy test.jar jar
        1 archivo(s) copiado(s).

C:\ws\eta\eta-first\dist\build\eta-0.8.6.4\eta-first-0.1.0.0\x\test\build\test>cd jar

C:\ws\eta\eta-first\dist\build\eta-0.8.6.4\eta-first-0.1.0.0\x\test\build\test\jar>jar xfv test.jar
 inflado: eta/first/Utils.class
 inflado: main/Main$$La$1.class
 inflado: main/Main$createFile.class
 inflado: main/Main$DZCmain.class
 inflado: main/Main$main.class
 inflado: main/Main$main1.class
 inflado: main/Main$main2.class
 inflado: main/Main$main3.class
 inflado: main/Main$main4.class
 inflado: main/Main.class
 inflado: eta/main.class
 inflado: META-INF/MANIFEST.MF

An important caveat: etlas is not aware of the contents of java files to trigger a fresh build so, for example, if you created the java file with another package you need to do a etlas clean before etlas run to trigger the build. Ignore that, etlas actually trigger the rebuild as i've just tested.

My Utils.java is:

package eta.first.test;

import java.nio.file.Files;
import java.nio.file.Paths;

public class Utils {

  /* This helper method lets us avoid variadic arguments which
     are a bit cumbersome to work with in Eta. */

  public static void createFile(String path) throws Exception {
    Files.createFile(Paths.get(path));
  }
}

[drever]

The class file is not in test.jar:

tar xfv test.jar                       
x main/Main$DZCmain.class
x main/Main$main.class
x main/Main$main1.class
x main/Main$main2.class
x main/Main$main3.class
x main/Main.class
x main/Primes$$Llvl1$1.class
x main/Primes$$wfilterPrime.class
x main/Primes$go.class
x main/Primes$primes.class
x main/Primes$sat.class
x main/Primes.class
x main/counter/datacons/Counter.class
x main/counter/tycons/Counter.class
x main/Counter$$fClass_Counter1.class
x main/Counter$$fClass_Counter_$cclassIdentifier.class
x main/Counter$$fClass_Counter_$cunobj.class
x main/Counter$$La$1.class
x main/Counter$$La1$1.class
x main/Counter$$La2$1.class
x main/Counter$$La3$1.class
x main/Counter$$La4$1.class
x main/Counter$$La5$1.class
x main/Counter$$La6$1.class
x main/Counter$$La7$1.class
x main/Counter$cOUNTER_MAX.class
x main/Counter$createFile.class
x main/Counter$DCounter.class
x main/Counter$get.class
x main/Counter$getPublicCounter.class
x main/Counter$increment.class
x main/Counter$newCounter.class
x main/Counter$newCounterWith.class
x main/Counter$set.class
x main/Counter.class
x eta/main.class
x META-INF/MANIFEST.MF

My Utils.java is more or less the same. When I introduce a syntax error I get a compile error, so I'm pretty sure that it is compiled correctly. The test file is created when the class is put on the class path manually.

[jneira]

Mmm, i wonder if it could be a mac (and linux?) specific issue, maybe @rahulmutt could help us to reproduce it

[rahulmutt]

@drever Perhaps you're using a version of Java > 9? There was a bug fix recently and there should be a release pretty soon that includes the fix.

[rahulmutt]

@drever Eta v0.8.6b5 is out - can you try it again and let me know if you still face the same issue?