8310314: Misplaced "unnamed classes are a preview feature and are disabled by default" error

Reviewed-by: jlaskey
Backport-of: 79069c5e748a274c45dec72aad082c31eff418d1

Author: lahodaj

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java

@@ -3995,6 +3995,7 @@ public JCTree.JCCompilationUnit parseCompilationUnit() {
                 }
 
                 if (isTopLevelMethodOrField) {
+                    checkSourceLevel(token.pos, Feature.UNNAMED_CLASSES);
                     defs.appendList(topLevelMethodOrFieldDeclaration(mods));
                     isUnnamedClass = true;
                 } else {
@@ -4025,8 +4026,6 @@ public JCTree.JCCompilationUnit parseCompilationUnit() {
 
     // Restructure top level to be an unnamed class.
     private List<JCTree> constructUnnamedClass(List<JCTree> origDefs) {
-        checkSourceLevel(Feature.UNNAMED_CLASSES);
-
         ListBuffer<JCTree> topDefs = new ListBuffer<>();
         ListBuffer<JCTree> defs = new ListBuffer<>();
 

test/langtools/tools/javac/unnamedclass/SourceLevelErrorPosition.java

@@ -0,0 +1,13 @@
+/**
+ * @test /nodynamiccopyright/
+ * @bug 8310314
+ * @summary Ensure proper error position for the "unnamed classes not supported" error
+ * @compile/fail/ref=SourceLevelErrorPosition.out -XDrawDiagnostics SourceLevelErrorPosition.java
+ */
+class Nested {}
+void main() {
+    System.err.println("");
+}
+void test() {
+    System.err.println("");
+}

test/langtools/tools/javac/unnamedclass/SourceLevelErrorPosition.out

@@ -0,0 +1,2 @@
+SourceLevelErrorPosition.java:8:1: compiler.err.preview.feature.disabled.plural: (compiler.misc.feature.unnamed.classes)
+1 error