Deprecate local variable support in SpEL's internal ExpressionState

Since the Spring Expression Language does not actually support local
variables in expressions, this commit deprecates all public APIs
related to local variables in ExpressionState (namely, the two
enterScope(...) variants that accept local variable data,
setLocalVariable(), and lookupLocalVariable()).

In addition, we no longer invoke `state.enterScope("index", ...)` in
the Projection and Selection AST nodes since the $index local variable
was never accessible within expressions anyway.

See gh-23202
Closes gh-32004

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

@@ -217,7 +217,9 @@ public void enterScope() {
 	 * name/value pair.
 	 * @param name the name of the local variable
 	 * @param value the value of the local variable
+	 * @deprecated as of 6.2 with no replacement; to be removed in 7.0
 	 */
+	@Deprecated(since = "6.2", forRemoval = true)
 	public void enterScope(String name, Object value) {
 		initVariableScopes().push(new VariableScope(name, value));
 		initScopeRootObjects().push(getActiveContextObject());
@@ -228,7 +230,9 @@ public void enterScope(String name, Object value) {
 	 * context object} and a new local variable scope containing the supplied
 	 * name/value pairs.
 	 * @param variables a map containing name/value pairs for local variables
+	 * @deprecated as of 6.2 with no replacement; to be removed in 7.0
 	 */
+	@Deprecated(since = "6.2", forRemoval = true)
 	public void enterScope(@Nullable Map<String, Object> variables) {
 		initVariableScopes().push(new VariableScope(variables));
 		initScopeRootObjects().push(getActiveContextObject());
@@ -246,7 +250,9 @@ public void exitScope() {
 	 * overwritten.
 	 * @param name the name of the local variable
 	 * @param value the value of the local variable
+	 * @deprecated as of 6.2 with no replacement; to be removed in 7.0
 	 */
+	@Deprecated(since = "6.2", forRemoval = true)
 	public void setLocalVariable(String name, Object value) {
 		initVariableScopes().element().setVariable(name, value);
 	}
@@ -256,7 +262,9 @@ public void setLocalVariable(String name, Object value) {
 	 * @param name the name of the local variable
 	 * @return the value of the local variable, or {@code null} if the variable
 	 * does not exist in the current scope
+	 * @deprecated as of 6.2 with no replacement; to be removed in 7.0
 	 */
+	@Deprecated(since = "6.2", forRemoval = true)
 	@Nullable
 	public Object lookupLocalVariable(String name) {
 		for (VariableScope scope : initVariableScopes()) {

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

@@ -93,7 +93,7 @@ protected ValueRef getValueRef(ExpressionState state) throws EvaluationException
 			for (Object element : data) {
 				try {
 					state.pushActiveContextObject(new TypedValue(element));
-					state.enterScope("index", result.size());
+					state.enterScope();
 					Object value = this.children[0].getValueInternal(state).getValue();
 					if (value != null && operandIsArray) {
 						arrayElementType = determineCommonType(arrayElementType, value.getClass());

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

@@ -139,11 +139,10 @@ protected ValueRef getValueRef(ExpressionState state) throws EvaluationException
 					Arrays.asList(ObjectUtils.toObjectArray(operand)));
 
 			List<Object> result = new ArrayList<>();
-			int index = 0;
 			for (Object element : data) {
 				try {
 					state.pushActiveContextObject(new TypedValue(element));
-					state.enterScope("index", index);
+					state.enterScope();
 					Object val = selectionCriteria.getValueInternal(state).getValue();
 					if (val instanceof Boolean b) {
 						if (b) {
@@ -157,7 +156,6 @@ protected ValueRef getValueRef(ExpressionState state) throws EvaluationException
 						throw new SpelEvaluationException(selectionCriteria.getStartPosition(),
 								SpelMessage.RESULT_OF_SELECTION_CRITERIA_IS_NOT_BOOLEAN);
 					}
-					index++;
 				}
 				finally {
 					state.exitScope();

spring-expression/src/test/java/org/springframework/expression/spel/ExpressionStateTests.java

@@ -56,6 +56,7 @@ void construction() {
 	}
 
 	@Test
+	@SuppressWarnings("removal")
 	void localVariables() {
 		Object value = state.lookupLocalVariable("foo");
 		assertThat(value).isNull();
@@ -86,6 +87,7 @@ void globalVariables() {
 	}
 
 	@Test
+	@SuppressWarnings("removal")
 	void noVariableInterference() {
 		TypedValue typedValue = state.lookupVariable("foo");
 		assertThat(typedValue).isEqualTo(TypedValue.NULL);
@@ -99,6 +101,7 @@ void noVariableInterference() {
 	}
 
 	@Test
+	@SuppressWarnings("removal")
 	void localVariableNestedScopes() {
 		assertThat(state.lookupLocalVariable("foo")).isNull();
 
@@ -157,6 +160,7 @@ void activeContextObject() {
 	}
 
 	@Test
+	@SuppressWarnings("removal")
 	void populatedNestedScopes() {
 		assertThat(state.lookupLocalVariable("foo")).isNull();
 
@@ -186,6 +190,7 @@ void rootObjectConstructor() {
 	}
 
 	@Test
+	@SuppressWarnings("removal")
 	void populatedNestedScopesMap() {
 		assertThat(state.lookupLocalVariable("foo")).isNull();
 		assertThat(state.lookupLocalVariable("goo")).isNull();