SpEL: ensure correct object used for nested #this references

Before this commit the object that #this would refer to in
nested expressions within projection/selection clauses was always
the root context object. This was incorrect as it should be the
element being projected/selected over. This commit introduces
a scope root context object which is set upon entering a new
scope (like when entering a projection or selection). Any
object. With this change this kind of expression now behaves:

where #this is the element of list1. Unqualified references
are also resolved against this scope root context object.

Issues: SPR-10417, SPR-12035, SPR-13055

spring-expression/src/main/java/org/springframework/expression/spel/ExpressionState.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.expression.spel;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -52,6 +53,15 @@ public class ExpressionState {
 
 	private final TypedValue rootObject;
 
+	// When entering a new scope there is a new base object which should be used
+	// for '#this' references (or to act as a target for unqualified references).
+	// This stack captures those objects at each nested scope level.
+	// For example: 
+	// #list1.?[#list2.contains(#this)]
+	// On entering the selection we enter a new scope, and #this is now the
+	// element from list1
+	private Stack<TypedValue> scopeRootObjects;
+
 	private final SpelParserConfiguration configuration;
 
 	private Stack<VariableScope> variableScopes;
@@ -86,6 +96,9 @@ public class ExpressionState {
 			// top level empty variable scope
 			this.variableScopes.add(new VariableScope());
 		}
+		if (this.scopeRootObjects == null) {
+			this.scopeRootObjects = new Stack<TypedValue>();
+		}
 	}
 
 	/**
@@ -116,6 +129,13 @@ public class ExpressionState {
 		return this.rootObject;
 	}
 
+	public TypedValue getScopeRootContextObject() {
+		if (this.scopeRootObjects == null || this.scopeRootObjects.isEmpty()) {
+			return this.rootObject;
+		}
+		return this.scopeRootObjects.peek();
+	}
+
 	public void setVariable(String name, Object value) {
 		this.relatedContext.setVariable(name, value);
 	}
@@ -158,16 +178,25 @@ public class ExpressionState {
 	public void enterScope(Map<String, Object> argMap) {
 		ensureVariableScopesInitialized();
 		this.variableScopes.push(new VariableScope(argMap));
+		this.scopeRootObjects.push(getActiveContextObject());
+	}
+	
+	public void enterScope() {
+		ensureVariableScopesInitialized();
+		this.variableScopes.push(new VariableScope(Collections.<String,Object>emptyMap()));
+		this.scopeRootObjects.push(getActiveContextObject());		
 	}
 
 	public void enterScope(String name, Object value) {
 		ensureVariableScopesInitialized();
 		this.variableScopes.push(new VariableScope(name, value));
+		this.scopeRootObjects.push(getActiveContextObject());
 	}
 
 	public void exitScope() {
 		ensureVariableScopesInitialized();
 		this.variableScopes.pop();
+		this.scopeRootObjects.pop();
 	}
 
 	public void setLocalVariable(String name, Object value) {

spring-expression/src/main/java/org/springframework/expression/spel/ast/MethodReference.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -150,7 +150,7 @@ public class MethodReference extends SpelNodeImpl {
 		for (int i = 0; i < arguments.length; i++) {
 			// Make the root object the active context again for evaluating the parameter expressions
 			try {
-				state.pushActiveContextObject(state.getRootContextObject());
+				state.pushActiveContextObject(state.getScopeRootContextObject());
 				arguments[i] = this.children[i].getValueInternal(state).getValue();
 			}
 			finally {

spring-expression/src/main/java/org/springframework/expression/spel/ast/Projection.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -68,17 +68,19 @@ public class Projection extends SpelNodeImpl {
 		// before calling the specified operation. This special context object
 		// has two fields 'key' and 'value' that refer to the map entries key
 		// and value, and they can be referenced in the operation
-		// eg. {'a':'y','b':'n'}.!{value=='y'?key:null}" == ['a', null]
+		// eg. {'a':'y','b':'n'}.![value=='y'?key:null]" == ['a', null]
 		if (operand instanceof Map) {
 			Map<?, ?> mapData = (Map<?, ?>) operand;
 			List<Object> result = new ArrayList<Object>();
 			for (Map.Entry<?, ?> entry : mapData.entrySet()) {
 				try {
 					state.pushActiveContextObject(new TypedValue(entry));
+					state.enterScope();
 					result.add(this.children[0].getValueInternal(state).getValue());
 				}
 				finally {
 					state.popActiveContextObject();
+					state.exitScope();
 				}
 			}
 			return new ValueRef.TypedValueHolderValueRef(new TypedValue(result), this);  // TODO unable to build correct type descriptor

spring-expression/src/main/java/org/springframework/expression/spel/ast/Selection.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -86,6 +86,7 @@ public class Selection extends SpelNodeImpl {
 				try {
 					TypedValue kvPair = new TypedValue(entry);
 					state.pushActiveContextObject(kvPair);
+					state.enterScope();
 					Object val = selectionCriteria.getValueInternal(state).getValue();
 					if (val instanceof Boolean) {
 						if ((Boolean) val) {
@@ -104,6 +105,7 @@ public class Selection extends SpelNodeImpl {
 				}
 				finally {
 					state.popActiveContextObject();
+					state.exitScope();
 				}
 			}
 			if ((this.variant == FIRST || this.variant == LAST) && result.isEmpty()) {