Extending CaseExpression, covering #1458 (#1459)

* Add unit tests for Case expressions.

* More tests for CaseExpression.

* Switch expression becomes an Expression instead of a Condition.
It allows complex expressions in the switch, similarly to what is allowed in when clauses.

Author: mgoeminne

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -4393,7 +4393,7 @@ Expression CaseWhenExpression() #CaseWhenExpression:
 }
 {
     <K_CASE> { caseCounter++; }
-    [ switchExp=Condition() ]
+    [ switchExp=Expression() ]
     ( clause=WhenThenSearchCondition() { whenClauses.add(clause); } )+
     [<K_ELSE> (LOOKAHEAD( ["("] CaseWhenExpression() [")"] ( <K_WHEN> | <K_ELSE> | <K_END> ) ) ["("] elseExp=CaseWhenExpression() [")" { ((CaseExpression) elseExp).setUsingBrackets(true); } ] 
               | elseExp=Expression()

src/test/java/net/sf/jsqlparser/expression/CaseExpressionTest.java

@@ -0,0 +1,84 @@
+/*-
+ * #%L
+ * JSQLParser library
+ * %%
+ * Copyright (C) 2004 - 2022 JSQLParser
+ * %%
+ * Dual licensed under GNU LGPL 2.1 or Apache License 2.0
+ * #L%
+ */
+package net.sf.jsqlparser.expression;
+
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.test.TestUtils;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Mathieu Goeminne
+ */
+public class CaseExpressionTest {
+    @Test
+    public void testSimpleCase() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseBinaryAndWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN true & false THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseBinaryOrWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN true | false THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseExclamationWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN !true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseNotWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN NOT true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseAndWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN true AND false THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseOrWhen() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true WHEN true OR false THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseExclamationSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE !true WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseNotSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE NOT true WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseBinaryAndSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true & false WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseBinaryOrSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true | false WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseAndSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true AND false WHEN true THEN 1 ELSE 2 END", true);
+    }
+
+    @Test
+    public void testCaseOrSwitch() throws JSQLParserException {
+        TestUtils.assertExpressionCanBeParsedAndDeparsed("CASE true OR false WHEN true THEN 1 ELSE 2 END", true);
+    }
+}