[ast] Store correct source position on ThisExpression

Previously, all ThisExpression's had kNoSourcePositions leading to
incorrect error messages like this:

  ➜ d8 -e "function t() { for (const x of this) {} } t();"
  unnamed:1: TypeError: undefined is not a function
  function t() { for (const x of this) {} } t();
            ^
  TypeError: undefined is not a function
      at t (unnamed:1:11)
      at unnamed:1:43


This patch allows creation of a ThisExpression with a source position,
leading to a better error message:

  ➜ d8  -e "function t() { for (const x of this) {} } t();"
  unnamed:1: TypeError: this is not iterable
  function t() { for (const x of this) {} } t();
                                 ^
  TypeError: this is not iterable
      at t (unnamed:1:32)
      at unnamed:1:43


This patch does not remove the existing cached version of
ThisExpression and instead creates a new one when required.

Bug: v8:6513
Change-Id: Idee4fe8946a9b821d06ff4a5e7eaefe54874ec59
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2345226Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69300}

src/ast/ast.h

@@ -1411,7 +1411,7 @@ class ThisExpression final : public Expression {
  private:
   friend class AstNodeFactory;
   friend Zone;
-  ThisExpression() : Expression(kNoSourcePosition, kThisExpression) {}
+  explicit ThisExpression(int pos) : Expression(pos, kThisExpression) {}
 };
 
 class VariableProxy final : public Expression {
@@ -2737,7 +2737,7 @@ class AstNodeFactory final {
       : zone_(zone),
         ast_value_factory_(ast_value_factory),
         empty_statement_(zone->New<class EmptyStatement>()),
-        this_expression_(zone->New<class ThisExpression>()),
+        this_expression_(zone->New<class ThisExpression>(kNoSourcePosition)),
         failure_expression_(zone->New<class FailureExpression>()) {}
 
   AstNodeFactory* ast_node_factory() { return this; }
@@ -2904,6 +2904,11 @@ class AstNodeFactory final {
     return this_expression_;
   }
 
+  class ThisExpression* NewThisExpression(int pos) {
+    DCHECK_NE(pos, kNoSourcePosition);
+    return zone_->New<class ThisExpression>(pos);
+  }
+
   class FailureExpression* FailureExpression() {
     return failure_expression_;
   }

src/parsing/parser-base.h

@@ -1833,7 +1833,7 @@ ParserBase<Impl>::ParsePrimaryExpression() {
 
     case Token::THIS: {
       Consume(Token::THIS);
-      return impl()->ThisExpression();
+      return impl()->NewThisExpression(beg_pos);
     }
 
     case Token::ASSIGN_DIV:

src/parsing/parser.h

@@ -786,6 +786,11 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
     return factory()->ThisExpression();
   }
 
+  class ThisExpression* NewThisExpression(int pos) {
+    UseThis();
+    return factory()->NewThisExpression(pos);
+  }
+
   Expression* NewSuperPropertyReference(int pos);
   Expression* NewSuperCallReference(int pos);
   Expression* NewTargetExpression(int pos);

src/parsing/preparser.h

@@ -1533,6 +1533,11 @@ class PreParser : public ParserBase<PreParser> {
     return PreParserExpression::This();
   }
 
+  V8_INLINE PreParserExpression NewThisExpression(int pos) {
+    UseThis();
+    return PreParserExpression::This();
+  }
+
   V8_INLINE PreParserExpression NewSuperPropertyReference(int pos) {
     scope()->NewUnresolved(factory()->ast_node_factory(),
                            ast_value_factory()->this_function_string(), pos,

test/message/fail/this-iterator-undefined.js

+// Copyright 2020 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.
+
+function t() {
+  for (const _ of this) {}
+}
+
+t();

test/message/fail/this-iterator-undefined.out

+# Copyright 2020 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.
+*%(basename)s:6: TypeError: this is not iterable
+  for (const _ of this) {}
+                  ^
+TypeError: this is not iterable
+    at t (*%(basename)s:6:19)
+    at *%(basename)s:9:1