Ensure SpEL ternary and Elvis expressions are enclosed in parentheses in toStringAST()

Prior to this commit, ternary and Elvis expressions enclosed in
parentheses (to account for operator precedence) were properly parsed
and evaluated; however, the corresponding toStringAST() implementations
did not enclose the results in parentheses. Consequently, the string
representation of the ASTs did not reflect the original semantics of
such expressions.

For example, given "(4 % 2 == 0 ? 1 : 0) * 10" as the expression to
parse and evaluate, the result of toStringAST() was previously
"(((4 % 2) == 0) ? 1 : 0 * 10)" instead of
"((((4 % 2) == 0) ? 1 : 0) * 10)", implying that 0 should be multiplied
by 10 instead of multiplying the result of the ternary expression by 10.

This commit addresses this by ensuring that SpEL ternary and Elvis
expressions are enclosed in parentheses in toStringAST().

Closes gh-29463

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -32,6 +32,7 @@ import org.springframework.util.ObjectUtils;
  *
  * @author Andy Clement
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 3.0
  */
 public class Elvis extends SpelNodeImpl {
@@ -64,7 +65,7 @@ public class Elvis extends SpelNodeImpl {
 
 	@Override
 	public String toStringAST() {
-		return getChild(0).toStringAST() + " ?: " + getChild(1).toStringAST();
+		return "(" + getChild(0).toStringAST() + " ?: " + getChild(1).toStringAST() + ")";
 	}
 
 	@Override

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -32,6 +32,7 @@ import org.springframework.util.ObjectUtils;
  *
  * @author Andy Clement
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 3.0
  */
 public class Ternary extends SpelNodeImpl {
@@ -62,7 +63,7 @@ public class Ternary extends SpelNodeImpl {
 
 	@Override
 	public String toStringAST() {
-		return getChild(0).toStringAST() + " ? " + getChild(1).toStringAST() + " : " + getChild(2).toStringAST();
+		return "(" + getChild(0).toStringAST() + " ? " + getChild(1).toStringAST() + " : " + getChild(2).toStringAST() + ")";
 	}
 
 	private void computeExitTypeDescriptor() {

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

@@ -116,6 +116,10 @@ class EvaluationTests extends AbstractExpressionTests {
 		void elvisOperator() {
 			evaluate("'Andy'?:'Dave'", "Andy", String.class);
 			evaluate("null?:'Dave'", "Dave", String.class);
+			evaluate("3?:1", 3, Integer.class);
+			evaluate("(2*3)?:1*10", 6, Integer.class);
+			evaluate("null?:2*10", 20, Integer.class);
+			evaluate("(null?:1)*10", 10, Integer.class);
 		}
 
 		@Test
@@ -624,6 +628,24 @@ class EvaluationTests extends AbstractExpressionTests {
 			evaluate("2>4?(3>2?true:false):(5<3?true:false)", false, Boolean.class);
 		}
 
+		@Test
+		void ternaryOperator06() {
+			evaluate("3?:#var=5", 3, Integer.class);
+			evaluate("null?:#var=5", 5, Integer.class);
+			evaluate("2>4?(3>2?true:false):(5<3?true:false)", false, Boolean.class);
+		}
+
+		@Test
+		void ternaryExpressionWithImplicitGrouping() {
+			evaluate("4 % 2 == 0 ? 2 : 3 * 10", 2, Integer.class);
+			evaluate("4 % 2 == 1 ? 2 : 3 * 10", 30, Integer.class);
+		}
+
+		@Test
+		void ternaryExpressionWithExplicitGrouping() {
+			evaluate("((4 % 2 == 0) ? 2 : 1) * 10", 20, Integer.class);
+		}
+
 		@Test
 		void ternaryOperatorWithNullValue() {
 			assertThatExceptionOfType(EvaluationException.class).isThrownBy(

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

@@ -162,7 +162,9 @@ class ParsingTests {
 
 	@Test
 	void elvis() {
-		parseCheck("3?:1", "3 ?: 1");
+		parseCheck("3?:1", "(3 ?: 1)");
+		parseCheck("(2*3)?:1*10", "((2 * 3) ?: (1 * 10))");
+		parseCheck("((2*3)?:1)*10", "(((2 * 3) ?: 1) * 10)");
 	}
 
 	// void relOperatorsIn01() {
@@ -404,13 +406,17 @@ class ParsingTests {
 
 	@Test
 	void ternaryOperator01() {
-		parseCheck("1>2?3:4", "(1 > 2) ? 3 : 4");
+		parseCheck("1>2?3:4", "((1 > 2) ? 3 : 4)");
+		parseCheck("(a ? 1 : 0) * 10", "((a ? 1 : 0) * 10)");
+		parseCheck("(a?1:0)*10", "((a ? 1 : 0) * 10)");
+		parseCheck("(4 % 2 == 0 ? 1 : 0) * 10", "((((4 % 2) == 0) ? 1 : 0) * 10)");
+		parseCheck("((4 % 2 == 0) ? 1 : 0) * 10", "((((4 % 2) == 0) ? 1 : 0) * 10)");
 	}
 
 	@Test
 	void ternaryOperator02() {
 		parseCheck("{1}.#isEven(#this) == 'y'?'it is even':'it is odd'",
-				"({1}.#isEven(#this) == 'y') ? 'it is even' : 'it is odd'");
+				"(({1}.#isEven(#this) == 'y') ? 'it is even' : 'it is odd')");
 	}
 
 	//