Bug 1363: Java 11: Document Java8 target constraints; Fix one odd compile issue

Document Java8 target constraints, i.e. where we need to set source, target and bootclasspath
to ensure target runtime Java8 compliance.

Fix one odd compile issue!
Using two theorethical identical GNU/Linux Debian 10 machines with same set of installed software,
one passes (like MacOS, Windows) and one fails.
The failure was due to the CStructAnnotationProcessor's @SupportedSourceVersion tag.
This downgrades the SourceVersion's previous bump from 6->11 (commit 610493b1724b5d91327f478338ff5d029bdcc032)
down to 8.

Interesting times ..

3 files changed, 8 insertions, 1 deletions

diff --git a/make/build-test.xml b/make/build-test.xml
index 8fc595e..5d7d75d 100644
--- a/make/build-test.xml
+++ b/make/build-test.xml
@@ -125,6 +125,7 @@
         <echo message=" build_t.gen     ${build_t.gen}"/>
 
         <!-- Javac of Annotation Processor dependencies - First -->
+        <!-- This has a hard Java8 target spec test: source, target + bootclasspath -->
         <javac destdir="${build_t.java}" 
                fork="yes"
                includeAntRuntime="false"
@@ -140,6 +141,7 @@
         </javac>
 
         <!-- Annotation Processor - Second -->
+        <!-- This has a hard Java8 target spec test: source, target + bootclasspath -->
         <mkdir dir="${build_t.gen}/classes/com/jogamp/gluegen/test/junit/structgen"/>
         <javac destdir="${build_t.java}" 
                fork="yes"
@@ -159,6 +161,7 @@
         </javac>
 
         <!-- Javac All - Third -->
+        <!-- This has a hard Java8 target spec test: source, target + bootclasspath -->
         <javac destdir="${build_t.java}" 
                fork="yes"
                includeAntRuntime="false"
diff --git a/make/build.xml b/make/build.xml
index ae91df5..12531ea 100644
--- a/make/build.xml
+++ b/make/build.xml
@@ -772,6 +772,7 @@
          original source in multiple stages below. -->
 
     <!-- Compile gluegen-rt first including generation of native headers -->
+    <!-- This has a hard Java8 target spec requirement: source, target + bootclasspath -->
     <javac destdir="${classes}"
            includeAntRuntime="false"
            includes="${gluegen-rt.classes} ${jogamp.common.classes}"
@@ -801,6 +802,7 @@
     </copy>
 
     <!-- Compile gluegen (compile time).  -->
+    <!-- This has a soft Java8 bytecote target only (Using some build time APIs): target -->
     <javac destdir="${classes}"
            includeAntRuntime="true"
            excludes="${gluegen.excludes.all} ${gluegen-rt.classes} ${java.part.android}"
@@ -1002,6 +1004,7 @@
 
   <target name="gluegen.build.android" if="android-jars.available">
     <!--compile gluegen-rt-android last-->
+    <!-- This has a hard Java8 target spec requirement: source, target + bootclasspath -->
     <javac destdir="${classes}"
            includeAntRuntime="false"
            includes="${gluegen-rt.classes} ${jogamp.common.classes}"
@@ -1138,6 +1141,7 @@
   </target>
 
   <target name="android-launcher.build" depends="gluegen.cpptasks.detect.os,gluegen.build.check.android-launcher" if="android-jars.available" unless="gluegen.build.skip.android-launcher">
+    <!-- This has a hard Java8 target spec requirement: source, target + bootclasspath -->
     <javac destdir="${classes}"
            includeAntRuntime="false"
            includes="${jogamp-android-launcher.classes}"
diff --git a/src/java/com/jogamp/gluegen/structgen/CStructAnnotationProcessor.java b/src/java/com/jogamp/gluegen/structgen/CStructAnnotationProcessor.java
index 45293f8..503b05f 100644
--- a/src/java/com/jogamp/gluegen/structgen/CStructAnnotationProcessor.java
+++ b/src/java/com/jogamp/gluegen/structgen/CStructAnnotationProcessor.java
@@ -85,7 +85,7 @@ import jogamp.common.Debug;
  * @author Michael Bien, et al.
  */
 @SupportedAnnotationTypes(value = {"com.jogamp.gluegen.structgen.CStruct", "com.jogamp.gluegen.structgen.CStructs"})
-@SupportedSourceVersion(SourceVersion.RELEASE_11)
+@SupportedSourceVersion(SourceVersion.RELEASE_8)
 public class CStructAnnotationProcessor extends AbstractProcessor {
     private static final String DEFAULT = "_default_";
     static final boolean DEBUG;