From f941754db668be5621b18c62e9a20aa9486c6d06 Mon Sep 17 00:00:00 2001
From: Sam Brannen <104798+sbrannen@users.noreply.github.com>
Date: Fri, 22 Mar 2024 16:29:38 +0100
Subject: [PATCH] Introduce isNullSafe() in SpelNodeImpl

Prior to this commit, MethodReference and PropertyOrFieldReference
already defined local isNullSafe() methods, but we need identical
methods in Selection, Projection, and Indexer, and we may potentially
need null-safe support for additional operators in the future.

To address the common need for an is-null-safe check, this commit
introduces an isNullSafe() method in SpelNodeImpl with a default
implementation that returns false.

Closes gh-32516
---
 .../expression/spel/ast/CompoundExpression.java    | 14 ++++++--------
 .../expression/spel/ast/MethodReference.java       |  3 ++-
 .../spel/ast/PropertyOrFieldReference.java         |  1 +
 .../expression/spel/ast/SpelNodeImpl.java          | 10 ++++++++++
 4 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/CompoundExpression.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/CompoundExpression.java
index 8a540a908dc..593e5164b0e 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/CompoundExpression.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/CompoundExpression.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,7 +24,6 @@ import org.springframework.expression.TypedValue;
 import org.springframework.expression.spel.CodeFlow;
 import org.springframework.expression.spel.ExpressionState;
 import org.springframework.expression.spel.SpelEvaluationException;
-import org.springframework.expression.spel.SpelNode;
 
 /**
  * Represents a DOT separated expression sequence, such as
@@ -120,14 +119,13 @@ public class CompoundExpression extends SpelNodeImpl {
 		for (int i = 0; i < getChildCount(); i++) {
 			sb.append(getChild(i).toStringAST());
 			if (i < getChildCount() - 1) {
-				SpelNode nextChild = getChild(i + 1);
+				SpelNodeImpl nextChild = this.children[i + 1];
+				if (nextChild.isNullSafe()) {
+					sb.append("?.");
+				}
 				// Don't append a '.' if the next child is an Indexer.
 				// For example, we want 'myVar[0]' instead of 'myVar.[0]'.
-				if (!(nextChild instanceof Indexer)) {
-					if ((nextChild instanceof MethodReference methodRef && methodRef.isNullSafe()) ||
-						(nextChild instanceof PropertyOrFieldReference pofRef && pofRef.isNullSafe())) {
-						sb.append('?');
-					}
+				else if (!(nextChild instanceof Indexer)) {
 					sb.append('.');
 				}
 			}
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java
index 3b60cff3ae3..ed0cdca8846 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -77,6 +77,7 @@ public class MethodReference extends SpelNodeImpl {
 	 * Does this node represent a null-safe method reference?
 	 * @since 6.0.13
 	 */
+	@Override
 	public final boolean isNullSafe() {
 		return this.nullSafe;
 	}
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/PropertyOrFieldReference.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/PropertyOrFieldReference.java
index a033f6c14b4..bb2e1719737 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/PropertyOrFieldReference.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/PropertyOrFieldReference.java
@@ -76,6 +76,7 @@ public class PropertyOrFieldReference extends SpelNodeImpl {
 	/**
 	 * Does this node represent a null-safe property or field reference?
 	 */
+	@Override
 	public boolean isNullSafe() {
 		return this.nullSafe;
 	}
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
index f6cbaa6c97c..3fb9208bc1b 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/SpelNodeImpl.java
@@ -181,6 +181,16 @@ public abstract class SpelNodeImpl implements SpelNode, Opcodes {
 		return this.endPos;
 	}
 
+	/**
+	 * Determine if this node is the target of a null-safe navigation operation.
+	 * <p>The default implementation returns {@code false}.
+	 * @return {@code true} if this node is the target of a null-safe operation
+	 * @since 6.1.6
+	 */
+	public boolean isNullSafe() {
+		return false;
+	}
+
 	/**
 	 * Check whether a node can be compiled to bytecode. The reasoning in each node may
 	 * be different but will typically involve checking whether the exit type descriptor