From ef0e0504f3a3aa3b576d8d890e8daeb906685d40 Mon Sep 17 00:00:00 2001
From: Mickael Istria <mistria@redhat.com>
Date: Mon, 4 Nov 2024 16:01:14 +0100
Subject: [PATCH] Better support for ASTParser.setFocalPoint()

Reduce the parsed AST before resolving to get a performance boost.
---
 .../dom/JavacCompilationUnitResolver.java     |  3 +++
 .../jdt/internal/javac/JavacUtils.java        | 27 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/core/dom/JavacCompilationUnitResolver.java b/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/core/dom/JavacCompilationUnitResolver.java
index 8f55f30dfef..478df74b8c3 100644
--- a/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/core/dom/JavacCompilationUnitResolver.java
+++ b/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();
 				}
diff --git a/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacUtils.java b/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacUtils.java
index 33e376c43e3..ec1144e9f91 100644
--- a/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacUtils.java
+++ b/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);
+				}
+			}
+		});
+	}
 }