[class] Fix early error for duplicate private fields

Bug: v8:8656
Change-Id: I86f00d377ac99a065c4ecf02abed08ec4feb3686
Reviewed-on: https://chromium-review.googlesource.com/c/1401214Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58650}

src/parsing/preparser.h

@@ -1251,7 +1251,10 @@ class PreParser : public ParserBase<PreParser> {
                                  class_info->computed_field_count),
           VariableMode::kConst);
     } else if (is_private && property_name.string_ != nullptr) {
-      scope()->DeclareVariableName(property_name.string_, VariableMode::kConst);
+      if (scope()->DeclareVariableName(property_name.string_,
+                                       VariableMode::kConst) == nullptr) {
+        ReportUnidentifiableError();
+      }
     }
   }
 

test/cctest/test-parsing.cc

@@ -5833,6 +5833,10 @@ TEST(PrivateClassFieldsErrors) {
     "#async a = 0",
     "#async a",
 
+    "#a; #a",
+    "#a = 1; #a",
+    "#a; #a = 1;",
+
     "#constructor",
     "#constructor = function() {}",
 
@@ -6010,6 +6014,9 @@ TEST(PrivateStaticClassFieldsErrors) {
     "#a = f(arguments)",
     "#a = () => () => arguments",
 
+    "#a; static #a",
+    "static #a; #a",
+
     // TODO(joyee): support static private methods
     "static #a() { }",
     "static get #a() { }",