Improve xml index expr type checking

compiler/ballerina-lang/src/main/java/org/ballerinalang/util/diagnostic/DiagnosticCode.java

@@ -318,6 +318,7 @@ public enum DiagnosticCode {
     UNSUPPORTED_METHOD_INVOCATION_XML_NAV("method.invocation.in.xml.navigation.expressions.not.supported"),
     DEPRECATED_XML_ATTRIBUTE_ACCESS("deprecated.xml.attribute.access.expression"),
     UNSUPPORTED_INDEX_IN_XML_NAVIGATION("indexing.within.xml.navigation.expression.not.supported"),
+    DEPRECATED_XML_CHILD_ACCESS("deprecated.xml.child.access"),
 
     UNDEFINED_ANNOTATION("undefined.annotation"),
     ANNOTATION_NOT_ALLOWED("annotation.not.allowed"),

compiler/ballerina-lang/src/main/java/org/wso2/ballerinalang/compiler/semantics/analyzer/TypeChecker.java

@@ -4640,7 +4640,15 @@ private BType checkIndexAccessExpr(BLangIndexBasedAccess indexBasedAccessExpr) {
                 return actualType;
             }
 
-            checkExpr(indexExpr, this.env);
+            BType indexExprType = checkExpr(indexExpr, this.env);
+            if (types.isAssignable(indexExprType, symTable.stringType)) {
+                dlog.warning(indexBasedAccessExpr.pos, DiagnosticCode.DEPRECATED_XML_CHILD_ACCESS);
+            } else if (!types.isAssignable(indexExprType, symTable.intType)) {
+                dlog.error(
+                        indexBasedAccessExpr.pos, DiagnosticCode.INCOMPATIBLE_TYPES, symTable.intType, indexExprType);
+                return symTable.semanticError;
+            }
+
             actualType = symTable.xmlType;
             indexBasedAccessExpr.originalType = actualType;
         } else if (varRefType == symTable.semanticError) {

compiler/ballerina-lang/src/main/resources/compiler.properties

@@ -1121,6 +1121,10 @@ warning.usage.of.deprecated.construct=\
 warning.non.module.qualified.error.reason=\
   error reason ''{0}'' is not module qualified
 
+warning.deprecated.xml.child.access=\
+  xml child access using member access is deprecated and will be removed in the next minor release. xml \
+  step expressions can now be used to access children.
+
 error.redeclared.import.module=\
   redeclared import module ''{0}''
 

tests/jballerina-unit-test/src/test/java/org/ballerinalang/test/types/xml/XMLAccessTest.java

@@ -213,9 +213,18 @@ public void testXMLNavigationExpressionWithQuotedIdentifiers() {
 
     @Test
     public void testInvalidXMLAccessWithIndex() {
-        BAssertUtil.validateError(negativeResult, 0, "cannot update an xml sequence", 5, 5);
+        int i = 0;
+        BAssertUtil.validateError(negativeResult, i++, "cannot update an xml sequence", 5, 5);
+        BAssertUtil.validateError(negativeResult, i++, "cannot update an xml sequence", 13, 5);
+        BAssertUtil.validateError(negativeResult, i++, "invalid assignment in variable 'x1/*'", 13, 5);
+        BAssertUtil.validateWarning(negativeResult, i++, "xml child access using member access is deprecated and " +
+                "will be removed in the next minor release. xml step expressions can now be used to access children.",
+                                    18, 13);
+        BAssertUtil.validateError(negativeResult, i++, "incompatible types: expected 'int', found 'boolean'", 19, 13);
+        BAssertUtil.validateError(negativeResult, i++, "incompatible types: expected 'int', found 'float'", 20, 13);
 
-        BAssertUtil.validateError(negativeResult, 1, "cannot update an xml sequence", 13, 5);
+        Assert.assertEquals(negativeResult.getErrorCount(), i - 1);
+        Assert.assertEquals(negativeResult.getWarnCount(), 1);
     }
 
     @Test

tests/jballerina-unit-test/src/test/resources/test-src/types/xml/xml-indexed-access-negative.bal

@@ -12,3 +12,10 @@ function testUpdatingGetAllChildren() {
     xml x2 = xml `<fruit>apple</fruit>`;
     x1/* = x2;
 }
+
+function testNonStringIndexAccess() {
+    xml x = xml `<elem></elem>`;
+    var c = x["child"];
+    var k = x[true];
+    var b = x[1.2];
+}