[debug] Include Token::CLASS in class scopes and ContainsPosition

While evaluating a class literal the containing function points to
Token::CLASS. It may have pushed a context for that class that uses
the range of the class scope. So far the class scope had a range that
started after the class name or class token in case of anonymous
classes. That means the source position of the function frame doesn't
point to a position that is included in the active context range. This
breaks the debugger because it relies on being able to find the
matching parser scope for the active context by looking at the source
position.

The fix is two-fold:
- extend the class scope source range to include Token::CLASS
- update ScopeChainRetriever::ContainsPosition to include the start
  position of class scopes as a valid source position. We can't always
  include start due to arrow functions that don't have braces.

Bug: chromium:1156498
Change-Id: I9ec640c6326289dadcb154bb0a329ca6f8188f8b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2857957Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74268}

src/debug/debug-scopes.cc

@@ -192,7 +192,13 @@ class ScopeChainRetriever {
     // functions that have the same end position.
     const bool position_fits_end =
         closure_scope_ ? position_ < end : position_ <= end;
-    return start < position_ && position_fits_end;
+    // While we're evaluating a class, the calling function will have a class
+    // context on the stack with a range that starts at Token::CLASS, and the
+    // source position will also point to Token::CLASS.  To identify the
+    // matching scope we include start in the accepted range for class scopes.
+    const bool position_fits_start =
+        scope->is_class_scope() ? start <= position_ : start < position_;
+    return position_fits_start && position_fits_end;
   }
 };
 

src/parsing/parser-base.h

@@ -4629,7 +4629,7 @@ typename ParserBase<Impl>::ExpressionT ParserBase<Impl>::ParseClassLiteral(
   ClassInfo class_info(this);
   class_info.is_anonymous = is_anonymous;
 
-  scope()->set_start_position(end_position());
+  scope()->set_start_position(class_token_pos);
   if (Check(Token::EXTENDS)) {
     ClassScope::HeritageParsingScope heritage(class_scope);
     FuncNameInferrerState fni_state(&fni_);

test/debugger/regress/regress-crbug-1156498.js

+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+const Debug = debug.Debug;
+Debug.setListener(function (event, exec_state, event_data, data) {
+});
+Debug.setBreakOnException();
+
+function f(){
+  (() => {
+    var out = 42;
+    var needsOut = () => {return out}
+    var simp_class = class {
+      static var1  = unreferenced;
+    }
+  })();
+}
+
+assertThrows(f, ReferenceError);