Snappy installation on macOS requests legacy Java SE 6 runtime

snap
#1

A number of users have struggled to get snappy working in recent macOS versions by
building jpy binary wheel. One common oddity was a failure running snappy-conf accompanied by a popup requesting installation of the legacy Java SE 6 runtime. This is a common issue for macOS users attempting to install applications that use the Java Native Interface (JNI). I recently obtained access to macOS Catalina and was able to reproduce this for SNAP 8 using:

sudo port install openjdk8-zulu

Rather than install the legacy package, I uninstalled openjdk8-zulu and ran:

sudo port install openjdk8-zulu +JNI

For this version, /Library/Java/JavaVirtualMachines/openjdk8-zulu/Contents/Info.plist has the section:

<key>JVMCapabilities</key>
                <array>
                        <string>JNI</string>
                        <string>CommandLine</string>
                </array>

The line <string>JNI</string> was not present in the version installed without the +JNI option.

[edit] Looking at the Portfile, installing the +JNI variant just makes the above
edit to Info.plist to:

Advertise the JVM capability “BundledApp”. This is required by some java-based app bundles to recognize and use the JVM.

Additional notes:

  1. macOS users should set JAVA_JDK using the value returned by
    /usr/libexec/java_home, e.g.:
export JAVA_JDK=$(/usr/libexec/java_home)
export JAVA_HOME=$JAVA_JDK
  1. I used git clone https://github.com/jpy-consortium/jpy for the jpy-0.10.0-devel source.
    Two edits were needed. I have maven3 installed as mvn3, so edited setup.py to change mvn to mvn3 and rate CC=/opt/local/bin/gcc-mp-11 /usr/bin/python3 setup.py build maven bdist_wheel. This gave one error in org_jpy_PyLib.c:
% git diff src/main/c/jni/org_jpy_PyLib.c
diff --git a/src/main/c/jni/org_jpy_PyLib.c b/src/main/c/jni/org_jpy_PyLib.c
index 53cd7ef..4f62ef2 100644
--- a/src/main/c/jni/org_jpy_PyLib.c
+++ b/src/main/c/jni/org_jpy_PyLib.c
@@ -44,6 +44,7 @@ int copyPythonDictToJavaMap(JNIEnv *jenv, PyObject *pyDict, jobject jMap);
 
 static int JPy_InitThreads = 0;
 
+void JPy_free(void); // fix error: implicit declaration of function 'JPy_free' is invalid in C99
 //#define JPy_JNI_DEBUG 1
 #define JPy_JNI_DEBUG 0
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