From cb7279da811f7add2f2f6a3bfbf0528834354fa3 Mon Sep 17 00:00:00 2001
From: marja <marja@chromium.org>
Date: Tue, 24 Mar 2015 09:46:53 -0700
Subject: [PATCH] [strong] Check strong mode free variables against the global
 object.

Gather references to unbound variables where the reference (VariableProxy) is
inside strong mode. Check them against the global object when a script is bound
to a context (during compilation).

This CL only checks unbound variables which are not inside lazy functions - TBD
how do we solve that; alternatives: add developer mode which disables laziness /
do the check whenever lazy functions are really compiled.

BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1005063002

Cr-Commit-Position: refs/heads/master@{#27422}
---
 src/api.cc                                   |  35 ++++-
 src/messages.js                              |   1 +
 src/objects.h                                |  24 ++-
 src/parser.cc                                |   4 +
 src/pending-compilation-error-handler.cc     |   4 +-
 src/pending-compilation-error-handler.h      |  18 ++-
 src/scopeinfo.cc                             |  77 +++++++++-
 src/scopes.cc                                |  16 +-
 src/scopes.h                                 |   5 +-
 src/variables.cc                             |   3 +
 src/variables.h                              |  24 +++
 test/cctest/test-parsing.cc                  | 150 +++++++++++++++++++
 test/mjsunit/strong/declaration-after-use.js |   3 +
 13 files changed, 344 insertions(+), 20 deletions(-)

diff --git a/src/api.cc b/src/api.cc
index 78328b74f..af164514b 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -22,6 +22,7 @@
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
+#include "src/contexts.h"
 #include "src/conversions-inl.h"
 #include "src/counters.h"
 #include "src/cpu-profiler.h"
@@ -36,6 +37,7 @@
 #include "src/messages.h"
 #include "src/natives.h"
 #include "src/parser.h"
+#include "src/pending-compilation-error-handler.h"
 #include "src/profile-generator-inl.h"
 #include "src/property.h"
 #include "src/property-details.h"
@@ -1497,9 +1499,36 @@ Local<Script> UnboundScript::BindToCurrentContext() {
       i::Handle<i::HeapObject>::cast(Utils::OpenHandle(this));
   i::Handle<i::SharedFunctionInfo>
       function_info(i::SharedFunctionInfo::cast(*obj), obj->GetIsolate());
+  i::Isolate* isolate = obj->GetIsolate();
+
+  i::ScopeInfo* scope_info = function_info->scope_info();
+  i::Handle<i::JSReceiver> global(isolate->native_context()->global_object());
+  for (int i = 0; i < scope_info->StrongModeFreeVariableCount(); ++i) {
+    i::Handle<i::String> name_string(scope_info->StrongModeFreeVariableName(i));
+    i::ScriptContextTable::LookupResult result;
+    i::Handle<i::ScriptContextTable> script_context_table(
+        isolate->native_context()->script_context_table());
+    if (!i::ScriptContextTable::Lookup(script_context_table, name_string,
+                                       &result)) {
+      i::Handle<i::Name> name(scope_info->StrongModeFreeVariableName(i));
+      Maybe<bool> has = i::JSReceiver::HasProperty(global, name);
+      if (has.IsJust() && !has.FromJust()) {
+        i::PendingCompilationErrorHandler pending_error_handler_;
+        pending_error_handler_.ReportMessageAt(
+            scope_info->StrongModeFreeVariableStartPosition(i),
+            scope_info->StrongModeFreeVariableEndPosition(i),
+            "strong_unbound_global", name_string, i::kReferenceError);
+        i::Handle<i::Script> script(i::Script::cast(function_info->script()));
+        pending_error_handler_.ThrowPendingError(isolate, script);
+        isolate->ReportPendingMessages();
+        isolate->OptionalRescheduleException(true);
+        return Local<Script>();
+      }
+    }
+  }
   i::Handle<i::JSFunction> function =
       obj->GetIsolate()->factory()->NewFunctionFromSharedFunctionInfo(
-          function_info, obj->GetIsolate()->native_context());
+          function_info, isolate->native_context());
   return ToApiHandle<Script>(function);
 }
 
@@ -1947,7 +1976,9 @@ MaybeLocal<Script> ScriptCompiler::Compile(Local<Context> context,
   i::Handle<i::SharedFunctionInfo> result(raw_result, isolate);
   Local<UnboundScript> generic = ToApiHandle<UnboundScript>(result);
   if (generic.IsEmpty()) return Local<Script>();
-  RETURN_ESCAPED(generic->BindToCurrentContext());
+  Local<Script> bound = generic->BindToCurrentContext();
+  if (bound.IsEmpty()) return Local<Script>();
+  RETURN_ESCAPED(bound);
 }
 
 
diff --git a/src/messages.js b/src/messages.js
index 12170c463..672fd4b81 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -172,6 +172,7 @@ var kMessages = {
   strong_for_in:                 ["In strong mode, 'for'-'in' loops are deprecated, use 'for'-'of' instead"],
   strong_empty:                  ["In strong mode, empty sub-statements are deprecated, make them explicit with '{}' instead"],
   strong_use_before_declaration: ["In strong mode, declaring variable '", "%0", "' before its use is required"],
+  strong_unbound_global:         ["In strong mode, using an undeclared global variable '", "%0", "' is not allowed"],
   strong_super_call_missing:     ["In strong mode, invoking the super constructor in a subclass is required"],
   strong_super_call_duplicate:   ["In strong mode, invoking the super constructor multiple times is deprecated"],
   strong_super_call_nested:      ["In strong mode, invoking the super constructor nested inside another statement or expression is deprecated"],
diff --git a/src/objects.h b/src/objects.h
index 347a1ee42..6b7682714 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4312,6 +4312,10 @@ class ScopeInfo : public FixedArray {
   // exposed to the user in a debugger.
   bool LocalIsSynthetic(int var);
 
+  String* StrongModeFreeVariableName(int var);
+  int StrongModeFreeVariableStartPosition(int var);
+  int StrongModeFreeVariableEndPosition(int var);
+
   // Lookup support for serialized scope info. Returns the
   // the stack slot index for a given slot name if the slot is
   // present; otherwise returns a value < 0. The name must be an internalized
@@ -4364,11 +4368,12 @@ class ScopeInfo : public FixedArray {
   // 3. The number of non-parameter variables allocated on the stack.
   // 4. The number of non-parameter and parameter variables allocated in the
   //    context.
-#define FOR_EACH_NUMERIC_FIELD(V)          \
-  V(Flags)                                 \
-  V(ParameterCount)                        \
-  V(StackLocalCount)                       \
-  V(ContextLocalCount)
+#define FOR_EACH_NUMERIC_FIELD(V) \
+  V(Flags)                        \
+  V(ParameterCount)               \
+  V(StackLocalCount)              \
+  V(ContextLocalCount)            \
+  V(StrongModeFreeVariableCount)
 
 #define FIELD_ACCESSORS(name)                            \
   void Set##name(int value) {                            \
@@ -4415,7 +4420,12 @@ class ScopeInfo : public FixedArray {
   //    the context locals in ContextLocalNameEntries. One slot is used per
   //    context local, so in total this part occupies ContextLocalCount()
   //    slots in the array.
-  // 5. FunctionNameEntryIndex:
+  // 5. StrongModeFreeVariableNameEntries:
+  //    Stores the names of strong mode free variables.
+  // 6. StrongModeFreeVariablePositionEntries:
+  //    Stores the locations (start and end position) of strong mode free
+  //    variables.
+  // 7. FunctionNameEntryIndex:
   //    If the scope belongs to a named function expression this part contains
   //    information about the function variable. It always occupies two array
   //    slots:  a. The name of the function variable.
@@ -4424,6 +4434,8 @@ class ScopeInfo : public FixedArray {
   int StackLocalEntriesIndex();
   int ContextLocalNameEntriesIndex();
   int ContextLocalInfoEntriesIndex();
+  int StrongModeFreeVariableNameEntriesIndex();
+  int StrongModeFreeVariablePositionEntriesIndex();
   int FunctionNameEntryIndex();
 
   // Location of the function variable for named function expressions.
diff --git a/src/parser.cc b/src/parser.cc
index fddd81b2f..afe51b288 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -3666,6 +3666,10 @@ bool CheckAndDeclareArrowParameter(ParserTraits* traits, Expression* expression,
       return false;
     }
 
+    // When the variable was seen, it was recorded as unresolved in the outer
+    // scope. But it's really not unresolved.
+    scope->outer_scope()->RemoveUnresolved(expression->AsVariableProxy());
+
     scope->DeclareParameter(raw_name, VAR);
     ++(*num_params);
     return true;
diff --git a/src/pending-compilation-error-handler.cc b/src/pending-compilation-error-handler.cc
index 230b87679..f0449d82a 100644
--- a/src/pending-compilation-error-handler.cc
+++ b/src/pending-compilation-error-handler.cc
@@ -17,7 +17,7 @@ void PendingCompilationErrorHandler::ThrowPendingError(Isolate* isolate,
   if (!has_pending_error_) return;
   MessageLocation location(script, start_position_, end_position_);
   Factory* factory = isolate->factory();
-  bool has_arg = arg_ != NULL || char_arg_ != NULL;
+  bool has_arg = arg_ != NULL || char_arg_ != NULL || !handle_arg_.is_null();
   Handle<FixedArray> elements = factory->NewFixedArray(has_arg ? 1 : 0);
   if (arg_ != NULL) {
     Handle<String> arg_string = arg_->string();
@@ -26,6 +26,8 @@ void PendingCompilationErrorHandler::ThrowPendingError(Isolate* isolate,
     Handle<String> arg_string =
         factory->NewStringFromUtf8(CStrVector(char_arg_)).ToHandleChecked();
     elements->set(0, *arg_string);
+  } else if (!handle_arg_.is_null()) {
+    elements->set(0, *handle_arg_);
   }
   isolate->debug()->OnCompileError(script);
 
diff --git a/src/pending-compilation-error-handler.h b/src/pending-compilation-error-handler.h
index 60923d649..c75f23d03 100644
--- a/src/pending-compilation-error-handler.h
+++ b/src/pending-compilation-error-handler.h
@@ -7,13 +7,12 @@
 
 #include "src/base/macros.h"
 #include "src/globals.h"
+#include "src/handles.h"
 
 namespace v8 {
 namespace internal {
 
 class AstRawString;
-template <class T>
-class Handle;
 class Isolate;
 class Script;
 
@@ -56,6 +55,20 @@ class PendingCompilationErrorHandler {
     error_type_ = error_type;
   }
 
+  void ReportMessageAt(int start_position, int end_position,
+                       const char* message, Handle<String> arg,
+                       ParseErrorType error_type = kSyntaxError) {
+    if (has_pending_error_) return;
+    has_pending_error_ = true;
+    start_position_ = start_position;
+    end_position_ = end_position;
+    message_ = message;
+    char_arg_ = nullptr;
+    arg_ = nullptr;
+    handle_arg_ = arg;
+    error_type_ = error_type;
+  }
+
   bool has_pending_error() const { return has_pending_error_; }
 
   void ThrowPendingError(Isolate* isolate, Handle<Script> script);
@@ -67,6 +80,7 @@ class PendingCompilationErrorHandler {
   const char* message_;
   const AstRawString* arg_;
   const char* char_arg_;
+  Handle<String> handle_arg_;
   ParseErrorType error_type_;
 
   DISALLOW_COPY_AND_ASSIGN(PendingCompilationErrorHandler);
diff --git a/src/scopeinfo.cc b/src/scopeinfo.cc
index d62bc4129..99d4c3829 100644
--- a/src/scopeinfo.cc
+++ b/src/scopeinfo.cc
@@ -18,9 +18,14 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone,
   // Collect stack and context locals.
   ZoneList<Variable*> stack_locals(scope->StackLocalCount(), zone);
   ZoneList<Variable*> context_locals(scope->ContextLocalCount(), zone);
-  scope->CollectStackAndContextLocals(&stack_locals, &context_locals);
+  ZoneList<Variable*> strong_mode_free_variables(0, zone);
+
+  scope->CollectStackAndContextLocals(&stack_locals, &context_locals,
+                                      &strong_mode_free_variables);
   const int stack_local_count = stack_locals.length();
   const int context_local_count = context_locals.length();
+  const int strong_mode_free_variable_count =
+      strong_mode_free_variables.length();
   // Make sure we allocate the correct amount.
   DCHECK(scope->StackLocalCount() == stack_local_count);
   DCHECK(scope->ContextLocalCount() == context_local_count);
@@ -49,9 +54,10 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone,
 
   const bool has_function_name = function_name_info != NONE;
   const int parameter_count = scope->num_parameters();
-  const int length = kVariablePartIndex
-      + parameter_count + stack_local_count + 2 * context_local_count
-      + (has_function_name ? 2 : 0);
+  const int length = kVariablePartIndex + parameter_count + stack_local_count +
+                     2 * context_local_count +
+                     3 * strong_mode_free_variable_count +
+                     (has_function_name ? 2 : 0);
 
   Factory* factory = isolate->factory();
   Handle<ScopeInfo> scope_info = factory->NewScopeInfo(length);
@@ -71,6 +77,7 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone,
   scope_info->SetParameterCount(parameter_count);
   scope_info->SetStackLocalCount(stack_local_count);
   scope_info->SetContextLocalCount(context_local_count);
+  scope_info->SetStrongModeFreeVariableCount(strong_mode_free_variable_count);
 
   int index = kVariablePartIndex;
   // Add parameters.
@@ -113,6 +120,25 @@ Handle<ScopeInfo> ScopeInfo::Create(Isolate* isolate, Zone* zone,
     scope_info->set(index++, Smi::FromInt(value));
   }
 
+  DCHECK(index == scope_info->StrongModeFreeVariableNameEntriesIndex());
+  for (int i = 0; i < strong_mode_free_variable_count; ++i) {
+    scope_info->set(index++, *strong_mode_free_variables[i]->name());
+  }
+
+  DCHECK(index == scope_info->StrongModeFreeVariablePositionEntriesIndex());
+  for (int i = 0; i < strong_mode_free_variable_count; ++i) {
+    // Unfortunately, the source code positions are stored as int even though
+    // int32_t would be enough (given the maximum source code length).
+    Handle<Object> start_position = factory->NewNumberFromInt(
+        static_cast<int32_t>(strong_mode_free_variables[i]
+                                 ->strong_mode_reference_start_position()));
+    scope_info->set(index++, *start_position);
+    Handle<Object> end_position = factory->NewNumberFromInt(
+        static_cast<int32_t>(strong_mode_free_variables[i]
+                                 ->strong_mode_reference_end_position()));
+    scope_info->set(index++, *end_position);
+  }
+
   // If present, add the function variable name and its index.
   DCHECK(index == scope_info->FunctionNameEntryIndex());
   if (has_function_name) {
@@ -285,6 +311,35 @@ bool ScopeInfo::LocalIsSynthetic(int var) {
 }
 
 
+String* ScopeInfo::StrongModeFreeVariableName(int var) {
+  DCHECK(0 <= var && var < StrongModeFreeVariableCount());
+  int info_index = StrongModeFreeVariableNameEntriesIndex() + var;
+  return String::cast(get(info_index));
+}
+
+
+int ScopeInfo::StrongModeFreeVariableStartPosition(int var) {
+  DCHECK(0 <= var && var < StrongModeFreeVariableCount());
+  int info_index = StrongModeFreeVariablePositionEntriesIndex() + var * 2;
+  int32_t value = 0;
+  bool ok = get(info_index)->ToInt32(&value);
+  USE(ok);
+  DCHECK(ok);
+  return value;
+}
+
+
+int ScopeInfo::StrongModeFreeVariableEndPosition(int var) {
+  DCHECK(0 <= var && var < StrongModeFreeVariableCount());
+  int info_index = StrongModeFreeVariablePositionEntriesIndex() + var * 2 + 1;
+  int32_t value = 0;
+  bool ok = get(info_index)->ToInt32(&value);
+  USE(ok);
+  DCHECK(ok);
+  return value;
+}
+
+
 int ScopeInfo::StackSlotIndex(String* name) {
   DCHECK(name->IsInternalizedString());
   if (length() > 0) {
@@ -432,11 +487,23 @@ int ScopeInfo::ContextLocalInfoEntriesIndex() {
 }
 
 
-int ScopeInfo::FunctionNameEntryIndex() {
+int ScopeInfo::StrongModeFreeVariableNameEntriesIndex() {
   return ContextLocalInfoEntriesIndex() + ContextLocalCount();
 }
 
 
+int ScopeInfo::StrongModeFreeVariablePositionEntriesIndex() {
+  return StrongModeFreeVariableNameEntriesIndex() +
+         StrongModeFreeVariableCount();
+}
+
+
+int ScopeInfo::FunctionNameEntryIndex() {
+  return StrongModeFreeVariablePositionEntriesIndex() +
+         2 * StrongModeFreeVariableCount();
+}
+
+
 int ContextSlotCache::Hash(Object* data, String* name) {
   // Uses only lower 32 bits if pointers are larger.
   uintptr_t addr_hash =
diff --git a/src/scopes.cc b/src/scopes.cc
index 97fbc2144..3d46d158a 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -586,8 +586,9 @@ class VarAndOrder {
 };
 
 
-void Scope::CollectStackAndContextLocals(ZoneList<Variable*>* stack_locals,
-                                         ZoneList<Variable*>* context_locals) {
+void Scope::CollectStackAndContextLocals(
+    ZoneList<Variable*>* stack_locals, ZoneList<Variable*>* context_locals,
+    ZoneList<Variable*>* strong_mode_free_variables) {
   DCHECK(stack_locals != NULL);
   DCHECK(context_locals != NULL);
 
@@ -621,6 +622,11 @@ void Scope::CollectStackAndContextLocals(ZoneList<Variable*>* stack_locals,
        p != NULL;
        p = variables_.Next(p)) {
     Variable* var = reinterpret_cast<Variable*>(p->value);
+    if (strong_mode_free_variables && var->has_strong_mode_reference() &&
+        var->mode() == DYNAMIC_GLOBAL) {
+      strong_mode_free_variables->Add(var, zone());
+    }
+
     if (var->is_used()) {
       vars.Add(VarAndOrder(var, p->order), zone());
     }
@@ -1107,6 +1113,12 @@ bool Scope::ResolveVariable(ParseInfo* info, VariableProxy* proxy,
   DCHECK(var != NULL);
   if (proxy->is_assigned()) var->set_maybe_assigned();
 
+  if (is_strong(language_mode())) {
+    // Record that the variable is referred to from strong mode. Also, record
+    // the position.
+    var->RecordStrongModeReference(proxy->position(), proxy->end_position());
+  }
+
   proxy->BindTo(var);
 
   return true;
diff --git a/src/scopes.h b/src/scopes.h
index 1197df9a2..cce8c3c9e 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -414,8 +414,9 @@ class Scope: public ZoneObject {
   // Collect stack and context allocated local variables in this scope. Note
   // that the function variable - if present - is not collected and should be
   // handled separately.
-  void CollectStackAndContextLocals(ZoneList<Variable*>* stack_locals,
-                                    ZoneList<Variable*>* context_locals);
+  void CollectStackAndContextLocals(
+      ZoneList<Variable*>* stack_locals, ZoneList<Variable*>* context_locals,
+      ZoneList<Variable*>* strong_mode_free_variables = nullptr);
 
   // Current number of var or const locals.
   int num_var_or_const() { return num_var_or_const_; }
diff --git a/src/variables.cc b/src/variables.cc
index 4f1f589eb..c0b8bd784 100644
--- a/src/variables.cc
+++ b/src/variables.cc
@@ -42,6 +42,9 @@ Variable::Variable(Scope* scope, const AstRawString* name, VariableMode mode,
       location_(UNALLOCATED),
       index_(-1),
       initializer_position_(RelocInfo::kNoPosition),
+      has_strong_mode_reference_(false),
+      strong_mode_reference_start_position_(RelocInfo::kNoPosition),
+      strong_mode_reference_end_position_(RelocInfo::kNoPosition),
       local_if_not_shadowed_(NULL),
       force_context_allocation_(false),
       is_used_(false),
diff --git a/src/variables.h b/src/variables.h
index 31fc4a60e..545c3bd1f 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -128,6 +128,25 @@ class Variable: public ZoneObject {
 
   static int CompareIndex(Variable* const* v, Variable* const* w);
 
+  void RecordStrongModeReference(int start_position, int end_position) {
+    // Record the earliest reference to the variable. Used in error messages for
+    // strong mode references to undeclared variables.
+    if (has_strong_mode_reference_ &&
+        strong_mode_reference_start_position_ < start_position)
+      return;
+    has_strong_mode_reference_ = true;
+    strong_mode_reference_start_position_ = start_position;
+    strong_mode_reference_end_position_ = end_position;
+  }
+
+  bool has_strong_mode_reference() const { return has_strong_mode_reference_; }
+  int strong_mode_reference_start_position() const {
+    return strong_mode_reference_start_position_;
+  }
+  int strong_mode_reference_end_position() const {
+    return strong_mode_reference_end_position_;
+  }
+
  private:
   Scope* scope_;
   const AstRawString* name_;
@@ -136,6 +155,11 @@ class Variable: public ZoneObject {
   Location location_;
   int index_;
   int initializer_position_;
+  // Tracks whether the variable is bound to a VariableProxy which is in strong
+  // mode, and if yes, the source location of the reference.
+  bool has_strong_mode_reference_;
+  int strong_mode_reference_start_position_;
+  int strong_mode_reference_end_position_;
 
   // If this field is set, this variable references the stored locally bound
   // variable, but it might be shadowed by variable bindings introduced by
diff --git a/test/cctest/test-parsing.cc b/test/cctest/test-parsing.cc
index 9d47ec1a2..5b19746f9 100644
--- a/test/cctest/test-parsing.cc
+++ b/test/cctest/test-parsing.cc
@@ -5638,3 +5638,153 @@ TEST(ArrowFunctionASIErrors) {
   RunParserSyncTest(context_data, data, kError, NULL, 0, always_flags,
                     arraysize(always_flags));
 }
+
+
+TEST(StrongModeFreeVariablesDeclaredByPreviousScript) {
+  i::FLAG_strong_mode = true;
+  v8::V8::Initialize();
+  v8::HandleScope scope(CcTest::isolate());
+  v8::Context::Scope context_scope(v8::Context::New(CcTest::isolate()));
+  v8::TryCatch try_catch;
+
+  // Introduce a bunch of variables, in all language modes.
+  const char* script1 =
+      "var my_var1 = 0;        \n"
+      "function my_func1() { } \n"
+      "const my_const1 = 0;    \n";
+  CompileRun(v8_str(script1));
+  CHECK(!try_catch.HasCaught());
+
+  const char* script2 =
+      "\"use strict\";         \n"
+      "let my_var2 = 0;        \n"
+      "function my_func2() { } \n"
+      "const my_const2 = 0     \n";
+  CompileRun(v8_str(script2));
+  CHECK(!try_catch.HasCaught());
+
+  const char* script3 =
+      "\"use strong\";         \n"
+      "let my_var3 = 0;        \n"
+      "function my_func3() { } \n"
+      "const my_const3 = 0;    \n";
+  CompileRun(v8_str(script3));
+  CHECK(!try_catch.HasCaught());
+
+  // Sloppy eval introduces variables in the surrounding scope.
+  const char* script4 =
+      "eval('var my_var4 = 0;')        \n"
+      "eval('function my_func4() { }') \n"
+      "eval('const my_const4 = 0;')    \n";
+  CompileRun(v8_str(script4));
+  CHECK(!try_catch.HasCaught());
+
+  // Test that referencing these variables work.
+  const char* script5 =
+      "\"use strong\";         \n"
+      "my_var1;                \n"
+      "my_func1;               \n"
+      "my_const1;              \n"
+      "my_var2;                \n"
+      "my_func2;               \n"
+      "my_const2;              \n"
+      "my_var3;                \n"
+      "my_func3;               \n"
+      "my_const3;              \n"
+      "my_var4;                \n"
+      "my_func4;               \n"
+      "my_const4;              \n";
+  CompileRun(v8_str(script5));
+  CHECK(!try_catch.HasCaught());
+}
+
+
+TEST(StrongModeFreeVariablesDeclaredByLanguage) {
+  i::FLAG_strong_mode = true;
+  v8::V8::Initialize();
+  v8::HandleScope scope(CcTest::isolate());
+  v8::Context::Scope context_scope(v8::Context::New(CcTest::isolate()));
+  v8::TryCatch try_catch;
+
+  const char* script1 =
+      "\"use strong\";         \n"
+      "Math;                   \n"
+      "RegExp;                 \n";
+  CompileRun(v8_str(script1));
+  CHECK(!try_catch.HasCaught());
+}
+
+
+TEST(StrongModeFreeVariablesDeclaredInGlobalPrototype) {
+  i::FLAG_strong_mode = true;
+  v8::V8::Initialize();
+  v8::HandleScope scope(CcTest::isolate());
+  v8::Context::Scope context_scope(v8::Context::New(CcTest::isolate()));
+  v8::TryCatch try_catch;
+
+  const char* script1 = "this.__proto__.my_var = 0;\n";
+  CompileRun(v8_str(script1));
+  CHECK(!try_catch.HasCaught());
+
+  const char* script2 =
+      "\"use strong\";         \n"
+      "my_var;                 \n";
+  CompileRun(v8_str(script2));
+  CHECK(!try_catch.HasCaught());
+}
+
+
+TEST(StrongModeFreeVariablesNotDeclared) {
+  i::FLAG_strong_mode = true;
+  v8::V8::Initialize();
+  v8::HandleScope scope(CcTest::isolate());
+  v8::Context::Scope context_scope(v8::Context::New(CcTest::isolate()));
+  v8::TryCatch try_catch;
+
+  // Test that referencing unintroduced variables in sloppy mode is ok.
+  const char* script1 =
+      "if (false) {            \n"
+      "  not_there1;           \n"
+      "}                       \n";
+  CompileRun(v8_str(script1));
+  CHECK(!try_catch.HasCaught());
+
+  // But not in strong mode.
+  {
+    const char* script2 =
+        "\"use strong\";         \n"
+        "if (false) {            \n"
+        "  not_there2;           \n"
+        "}                       \n";
+    v8::TryCatch try_catch2;
+    v8::Script::Compile(v8_str(script2));
+    CHECK(try_catch2.HasCaught());
+    v8::String::Utf8Value exception(try_catch2.Exception());
+    CHECK_EQ(0,
+             strcmp(
+                 "ReferenceError: In strong mode, using an undeclared global "
+                 "variable 'not_there2' is not allowed",
+                 *exception));
+  }
+
+  // Check that the variable reference is detected inside a strong function too,
+  // even if the script scope is not strong.
+  {
+    const char* script3 =
+        "(function not_lazy() {  \n"
+        "  \"use strong\";       \n"
+        "  if (false) {          \n"
+        "    not_there3;         \n"
+        "  }                     \n"
+        "})();                   \n";
+    v8::TryCatch try_catch2;
+    v8::Script::Compile(v8_str(script3));
+    CHECK(try_catch2.HasCaught());
+    v8::String::Utf8Value exception(try_catch2.Exception());
+    CHECK_EQ(0,
+             strcmp(
+                 "ReferenceError: In strong mode, using an undeclared global "
+                 "variable 'not_there3' is not allowed",
+                 *exception));
+  }
+}
diff --git a/test/mjsunit/strong/declaration-after-use.js b/test/mjsunit/strong/declaration-after-use.js
index a5be65056..aa5ff6728 100644
--- a/test/mjsunit/strong/declaration-after-use.js
+++ b/test/mjsunit/strong/declaration-after-use.js
@@ -208,6 +208,9 @@ function assertThrowsHelper(code) {
   let func5 = (p1, p2) => { p1; p2; };
   func5();
 
+  let func5b = p1 => p1;
+  func5b();
+
   function func6() {
     var1, var2a, var2b, var2c;
   }
-- 
2.34.1