Fix 'eval' in class extends clauses to be always-strict

Compiler backends get their language mode from the current
function, but should instead be deriving it from the current scope.
This allows proper handling of the always-strictness of class declarations
and expressions, and in particular the treatment of 'eval' calls in an
extends clause as a strict eval.

Also fix the parser's RecordEvalCall logic to only reach out to the
DeclarationScope in sloppy mode, which fixes the strange case of a
sloppy function thinking it contains a sloppy eval when in fact
it contains only a strict eval.

BUG=v8:4970
LOG=n

Review-Url: https://codereview.chromium.org/1931003003
Cr-Commit-Position: refs/heads/master@{#36001}

src/compiler/ast-graph-builder.cc

@@ -3080,7 +3080,7 @@ void AstGraphBuilder::VisitLogicalExpression(BinaryOperation* expr) {
 
 
 LanguageMode AstGraphBuilder::language_mode() const {
-  return info()->language_mode();
+  return current_scope()->language_mode();
 }
 
 

src/full-codegen/full-codegen.h

@@ -711,7 +711,7 @@ class FullCodeGenerator: public AstVisitor {
   Handle<Script> script() { return info_->script(); }
   bool is_eval() { return info_->is_eval(); }
   bool is_native() { return info_->is_native(); }
-  LanguageMode language_mode() { return literal()->language_mode(); }
+  LanguageMode language_mode() { return scope()->language_mode(); }
   bool has_simple_parameters() { return info_->has_simple_parameters(); }
   FunctionLiteral* literal() const { return info_->literal(); }
   Scope* scope() { return scope_; }

src/interpreter/bytecode-generator.cc

@@ -3276,7 +3276,7 @@ void BytecodeGenerator::VisitInScope(Statement* stmt, Scope* scope) {
 
 
 LanguageMode BytecodeGenerator::language_mode() const {
-  return info()->language_mode();
+  return execution_context()->scope()->language_mode();
 }
 
 

src/parsing/parser-base.h

@@ -904,8 +904,12 @@ class ParserBase : public Traits {
   void CheckPossibleEvalCall(ExpressionT expression, Scope* scope) {
     if (Traits::IsIdentifier(expression) &&
         Traits::IsEval(Traits::AsIdentifier(expression))) {
-      scope->DeclarationScope()->RecordEvalCall();
       scope->RecordEvalCall();
+      if (is_sloppy(scope->language_mode())) {
+        // For sloppy scopes we also have to record the call at function level,
+        // in case it includes declarations that will be hoisted.
+        scope->DeclarationScope()->RecordEvalCall();
+      }
     }
   }
 

test/mjsunit/regress/regress-4970.js

+// Copyright 2016 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.
+//
+// Flags: --allow-natives-syntax
+
+function g() {
+  var f;
+  class C extends eval("f = () => delete C; Array") {}
+  f();
+}
+
+assertThrows(g, SyntaxError);
+%OptimizeFunctionOnNextCall(g);
+assertThrows(g, SyntaxError);