Locate spot to generate TemplateExtensions.java better

When locating the folder to generate `TemplateExtension.java` into
during the "generate missing member" Qute quick fix:
- Filter out classpath entries that are in the output (`target`) folder
- Filter out classpath entries that represent test code
- Filter out classpath entries that represent resource folders (folders
  with no Java source files)

Fixes #831

Signed-off-by: David Thompson <davthomp@redhat.com>

qute.jdt/com.redhat.qute.jdt.test/projects/maven/qute-quickstart/.classpath

@@ -1,21 +1,21 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <classpath>
-	<classpathentry kind="src" output="target/classes" path="src/main/java">
+	<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
 		<attributes>
-			<attribute name="optional" value="true"/>
 			<attribute name="maven.pomderived" value="true"/>
 		</attributes>
 	</classpathentry>
-	<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
+	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
 		<attributes>
+			<attribute name="optional" value="true"/>
 			<attribute name="maven.pomderived" value="true"/>
+			<attribute name="test" value="true"/>
 		</attributes>
 	</classpathentry>
-	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
+	<classpathentry kind="src" output="target/classes" path="src/main/java">
 		<attributes>
 			<attribute name="optional" value="true"/>
 			<attribute name="maven.pomderived" value="true"/>
-			<attribute name="test" value="true"/>
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">

qute.jdt/com.redhat.qute.jdt/src/main/java/com/redhat/qute/jdt/internal/template/TemplateGenerateMissingJavaMember.java

@@ -11,16 +11,22 @@
 
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
+import java.util.Optional;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.stream.Stream;
 
 import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.jdt.core.Flags;
+import org.eclipse.jdt.core.IClasspathEntry;
 import org.eclipse.jdt.core.ICompilationUnit;
 import org.eclipse.jdt.core.IField;
+import org.eclipse.jdt.core.IJavaElement;
 import org.eclipse.jdt.core.IJavaProject;
 import org.eclipse.jdt.core.IPackageFragment;
 import org.eclipse.jdt.core.IPackageFragmentRoot;
@@ -378,9 +384,46 @@ private static WorkspaceEdit createNewTemplateExtensionFile(GenerateMissingJavaM
 
 		IPackageFragment destPackage = null;
 		try {
+
+			IPath targetFolder = project.getOutputLocation().removeLastSegments(1);
+
+			List<IClasspathEntry> sourceClassPathEntries = Stream.of(project.getRawClasspath()) //
+					.filter(cpe -> {
+						cpe.getExtraAttributes();
+						return cpe.getEntryKind() == IClasspathEntry.CPE_SOURCE && !cpe.isTest() && !targetFolder.isPrefixOf(cpe.getPath());
+					}) //
+					.toList();
+			if (sourceClassPathEntries.isEmpty()) {
+				throw new UnsupportedOperationException(
+						"Cannot locate source code folder");
+			}
+			Optional<IPackageFragmentRoot> sourceFragmentRootOptional = Stream.of(project.getPackageFragmentRoots()) //
+					.filter(pfr -> {
+						try {
+							if (pfr.getKind() == IPackageFragmentRoot.K_BINARY || pfr.getResource() == null) {
+								return false;
+							}
+							return Stream.of(pfr.getChildren()).anyMatch(child -> child.getElementType() == IJavaElement.PACKAGE_FRAGMENT);
+						} catch (JavaModelException e) {
+							return false;
+						}
+					}) //
+					.filter(pfr -> {
+						for (var cpe : sourceClassPathEntries) {
+							if (cpe.getPath().equals(pfr.getResource().getFullPath())) {
+								return true;
+							}
+						}
+						return false;
+					}) //
+					.findFirst();
+			if (sourceFragmentRootOptional.isEmpty()) {
+				throw new UnsupportedOperationException(
+						"Cannot locate source code folder");
+			}
+			IPackageFragmentRoot fragmentRoot = sourceFragmentRootOptional.get();
 			// TODO: longest substring match of package of original class
 			// OR: figure out the "correct" one from the groupId?
-			IPackageFragmentRoot fragmentRoot = project.getPackageFragmentRoots()[0];
 			destPackage = fragmentRoot.getPackageFragment("");
 		} catch (JavaModelException e) {
 		}