Fix #4912 - grammar for TWR allows this expression

pmd-java/etc/grammar/Java.jjt

@@ -2867,8 +2867,8 @@ void Resource() :
    PrimaryExpression()
    {
     Node top = jjtree.peekNode();
-    if (!(top instanceof ASTVariableAccess || top instanceof ASTFieldAccess))
-      throwParseException("Expected a variable access, but was a " + top.getXPathNodeName());
+    if (!(top instanceof ASTVariableAccess || top instanceof ASTFieldAccess || top instanceof ASTThisExpression))
+      throwParseException("Expected a variable or field access, but was a " + top.getXPathNodeName());
    }
    {}
 }

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/ASTResource.java

@@ -7,6 +7,7 @@ package net.sourceforge.pmd.lang.java.ast;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 import net.sourceforge.pmd.lang.ast.Node;
+import net.sourceforge.pmd.lang.java.ast.internal.PrettyPrintingUtil;
 
 /**
  * A resource of a {@linkplain ASTTryStatement try-with-resources}. This contains another
@@ -48,24 +49,16 @@ public final class ASTResource extends AbstractJavaNode {
      * then returns the sequence of names that identifies the expression.
      * If this has a local variable declaration, then returns the name
      * of the variable.
+     *
+     * <p>Note that this might be null if the expression is too complex.
+     *
+     * @deprecated Since 7.1.0. This method is not very useful because the expression
+     *          might be complex and not have a real "name".
      */
+    @Deprecated
     public String getStableName() {
         if (isConciseResource()) {
-            ASTExpression expr = getInitializer();
-            StringBuilder builder = new StringBuilder();
-            while (expr instanceof ASTFieldAccess) {
-                ASTFieldAccess fa = (ASTFieldAccess) expr;
-                builder.insert(0, "." + fa.getName());
-                expr = fa.getQualifier();
-            }
-            // the last one may be ambiguous, or a variable reference
-            // the only common interface we have to get their name is
-            // unfortunately Node::getImage
-
-            if (expr != null) {
-                builder.insert(0, expr.getImage());
-            }
-            return builder.toString();
+            return PrettyPrintingUtil.prettyPrint(getInitializer()).toString();
         } else {
             return asLocalVariableDeclaration().iterator().next().getName();
         }

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/internal/PrettyPrintingUtil.java

@@ -241,6 +241,7 @@ public final class PrettyPrintingUtil {
     }
 
 
+    /** Pretty print an expression or any other kind of node. */
     public static CharSequence prettyPrint(JavaNode node) {
         StringBuilder sb = new StringBuilder();
         node.acceptVisitor(new ExprPrinter(), sb);

pmd-java/src/test/kotlin/net/sourceforge/pmd/lang/java/ast/ASTTryStatementTest.kt

@@ -132,8 +132,16 @@ class ASTTryStatementTest : ParserTestSpec({
                 }
             }
 
+            // the expr must be a field access or var access
             "try ( a.foo() ){}" shouldNot parse()
             "try (new Foo()){}" shouldNot parse()
+            "try(arr[0]) {}" shouldNot parse()
+
+            "try ( a.foo().b ){}" should parse()
+            "try (new Foo().x){}" should parse()
+            // this is also allowed by javac
+            "try(this) {}" should parse()
+            "try(Foo.this) {}" should parse()
         }
     }