Better support for ASTParser.setFocalPoint()

Reduce the parsed AST before resolving to get a performance boost.

Author: mickaelistria

org.eclipse.jdt.core.javac/src/org/eclipse/jdt/core/dom/JavacCompilationUnitResolver.java

@@ -711,6 +711,9 @@ public Void visitClass(ClassTree node, Void p) {
 				if (elements.hasNext() && elements.next() instanceof JCCompilationUnit u) {
 					javacCompilationUnit = u;
 					javacCompilationUnits.add(u);
+					if (sourceUnits.length == 1 && focalPoint >= 0) {
+						JavacUtils.trimUnvisibleContent(u, focalPoint, context);
+					}
 				} else {
 					return Map.of();
 				}

org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacUtils.java

@@ -47,7 +47,13 @@
 
 import com.sun.tools.javac.file.JavacFileManager;
 import com.sun.tools.javac.main.Option;
+import com.sun.tools.javac.tree.JCTree.JCCompilationUnit;
+import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
+import com.sun.tools.javac.tree.TreeInfo;
+import com.sun.tools.javac.tree.TreeMaker;
+import com.sun.tools.javac.tree.TreeScanner;
 import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.Names;
 import com.sun.tools.javac.util.Options;
 
 public class JavacUtils {
@@ -409,4 +415,25 @@ public static boolean isTest(IJavaProject project, org.eclipse.jdt.internal.comp
 			return true;
 		}
 	}
+
+	/// Removes non-relevant content (eg other method blocks) for given focal position
+	public static void trimUnvisibleContent(JCCompilationUnit u, int focalPoint, Context context) {
+		TreeMaker treeMaker = TreeMaker.instance(context);
+		u.accept(new TreeScanner() {
+			@Override
+			public void visitMethodDef(JCMethodDecl decl) {
+				if (decl.getBody() != null &&
+					!decl.getBody().getStatements().isEmpty() &&
+					!(decl.getStartPosition() <= focalPoint &&
+					decl.getStartPosition() + TreeInfo.getEndPos(decl, u.endPositions) >= focalPoint)) {
+					var throwNewRuntimeExceptionOutOfFocalPositionScope =
+						treeMaker.Throw(
+								treeMaker.NewClass(null, null,
+										treeMaker.Ident(Names.instance(context).fromString(RuntimeException.class.getSimpleName())),
+										com.sun.tools.javac.util.List.of(treeMaker.Literal("Out of focalPosition scope")), null)); //$NON-NLS-1$
+					decl.body.stats = com.sun.tools.javac.util.List.of(throwNewRuntimeExceptionOutOfFocalPositionScope);
+				}
+			}
+		});
+	}
 }