[parser] Simplify Scope::DeclareVariable

Restructure the code a little, and change how we detect sloppy block function
redeclaration so we don't dereference a possibly nullptr function.

Bug: chromium:900786
Change-Id: Ief124fe767603ca36f4dc8865c4aeb3e0635b4cf
Reviewed-on: https://chromium-review.googlesource.com/c/1314331
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57206}

src/ast/ast.h

@@ -444,14 +444,26 @@ inline NestedVariableDeclaration* VariableDeclaration::AsNested() {
 class FunctionDeclaration final : public Declaration {
  public:
   FunctionLiteral* fun() const { return fun_; }
+  bool declares_sloppy_block_function() const {
+    return DeclaresSloppyBlockFunction::decode(bit_field_);
+  }
 
  private:
   friend class AstNodeFactory;
 
-  FunctionDeclaration(VariableProxy* proxy, FunctionLiteral* fun, int pos)
-      : Declaration(proxy, pos, kFunctionDeclaration), fun_(fun) {}
+  class DeclaresSloppyBlockFunction
+      : public BitField<bool, Declaration::kNextBitFieldIndex, 1> {};
+
+  FunctionDeclaration(VariableProxy* proxy, FunctionLiteral* fun,
+                      bool declares_sloppy_block_function, int pos)
+      : Declaration(proxy, pos, kFunctionDeclaration), fun_(fun) {
+    bit_field_ = DeclaresSloppyBlockFunction::update(
+        bit_field_, declares_sloppy_block_function);
+  }
 
   FunctionLiteral* fun_;
+
+  static const uint8_t kNextBitFieldIndex = DeclaresSloppyBlockFunction::kNext;
 };
 
 
@@ -2883,8 +2895,11 @@ class AstNodeFactory final {
   }
 
   FunctionDeclaration* NewFunctionDeclaration(VariableProxy* proxy,
-                                              FunctionLiteral* fun, int pos) {
-    return new (zone_) FunctionDeclaration(proxy, fun, pos);
+                                              FunctionLiteral* fun,
+                                              bool is_sloppy_block_function,
+                                              int pos) {
+    return new (zone_)
+        FunctionDeclaration(proxy, fun, is_sloppy_block_function, pos);
   }
 
   Block* NewBlock(int capacity, bool ignore_completion_value,

src/ast/scopes.cc

@@ -1058,8 +1058,7 @@ Variable* DeclarationScope::DeclareParameterName(
 }
 
 Variable* Scope::DeclareLocal(const AstRawString* name, VariableMode mode,
-                              InitializationFlag init_flag, VariableKind kind,
-                              MaybeAssignedFlag maybe_assigned_flag) {
+                              InitializationFlag init_flag) {
   DCHECK(!already_resolved_);
   // This function handles VariableMode::kVar, VariableMode::kLet, and
   // VariableMode::kConst modes.  VariableMode::kDynamic variables are
@@ -1070,7 +1069,7 @@ Variable* Scope::DeclareLocal(const AstRawString* name, VariableMode mode,
                  mode == VariableMode::kVar || mode == VariableMode::kLet ||
                      mode == VariableMode::kConst);
   DCHECK(!GetDeclarationScope()->was_lazily_parsed());
-  return Declare(zone(), name, mode, kind, init_flag, maybe_assigned_flag);
+  return Declare(zone(), name, mode, NORMAL_VARIABLE, init_flag);
 }
 
 Variable* Scope::DeclareVariable(
@@ -1094,7 +1093,6 @@ Variable* Scope::DeclareVariable(
   VariableProxy* proxy = declaration->proxy();
   DCHECK_NOT_NULL(proxy->raw_name());
   const AstRawString* name = proxy->raw_name();
-  bool is_function_declaration = declaration->IsFunctionDeclaration();
 
   // Pessimistically assume that top-level variables will be assigned.
   //
@@ -1107,70 +1105,54 @@ Variable* Scope::DeclareVariable(
     if (mode != VariableMode::kConst) proxy->set_is_assigned();
   }
 
-  Variable* var = nullptr;
-  if (is_eval_scope() && is_sloppy(language_mode()) &&
-      mode == VariableMode::kVar) {
-    // In a var binding in a sloppy direct eval, pollute the enclosing scope
-    // with this new binding by doing the following:
-    // The proxy is bound to a lookup variable to force a dynamic declaration
-    // using the DeclareEvalVar or DeclareEvalFunction runtime functions.
-    var = new (zone())
-        Variable(this, name, mode, NORMAL_VARIABLE, init, kMaybeAssigned);
-    var->AllocateTo(VariableLocation::LOOKUP, -1);
-  } else {
-    // Declare the variable in the declaration scope.
-    var = LookupLocal(name);
-    if (var == nullptr) {
+  Variable* var = LookupLocal(name);
+  // Declare the variable in the declaration scope.
+  if (V8_LIKELY(var == nullptr)) {
+    if (V8_UNLIKELY(is_eval_scope() && is_sloppy(language_mode()) &&
+                    mode == VariableMode::kVar)) {
+      // In a var binding in a sloppy direct eval, pollute the enclosing scope
+      // with this new binding by doing the following:
+      // The proxy is bound to a lookup variable to force a dynamic declaration
+      // using the DeclareEvalVar or DeclareEvalFunction runtime functions.
+      var = new (zone())
+          Variable(this, name, mode, NORMAL_VARIABLE, init, kMaybeAssigned);
+      var->AllocateTo(VariableLocation::LOOKUP, -1);
+    } else {
       // Declare the name.
-      VariableKind kind = NORMAL_VARIABLE;
-      if (is_function_declaration) {
-        kind = FUNCTION_VARIABLE;
-      }
-      var = DeclareLocal(name, mode, init, kind, kNotAssigned);
-    } else if (IsLexicalVariableMode(mode) ||
-               IsLexicalVariableMode(var->mode())) {
-      // Allow duplicate function decls for web compat, see bug 4693.
-      bool duplicate_allowed = false;
-      if (is_sloppy(language_mode()) && is_function_declaration &&
-          var->is_function()) {
-        DCHECK(IsLexicalVariableMode(mode) &&
-               IsLexicalVariableMode(var->mode()));
-        // If the duplication is allowed, then the var will show up
-        // in the SloppyBlockFunctionMap and the new FunctionKind
-        // will be a permitted duplicate.
-        FunctionKind function_kind =
-            declaration->AsFunctionDeclaration()->fun()->kind();
-        SloppyBlockFunctionMap* map =
-            GetDeclarationScope()->sloppy_block_function_map();
-        duplicate_allowed = map != nullptr &&
-                            map->Lookup(const_cast<AstRawString*>(name),
-                                        name->Hash()) != nullptr &&
-                            !IsAsyncFunction(function_kind) &&
-                            !IsGeneratorFunction(function_kind);
-      }
-      if (duplicate_allowed) {
-        *sloppy_mode_block_scope_function_redefinition = true;
-      } else {
-        // The name was declared in this scope before; check for conflicting
-        // re-declarations. We have a conflict if either of the declarations
-        // is not a var (in script scope, we also have to ignore legacy const
-        // for compatibility). There is similar code in runtime.cc in the
-        // Declare functions. The function CheckConflictingVarDeclarations
-        // checks for var and let bindings from different scopes whereas this
-        // is a check for conflicting declarations within the same scope. This
-        // check also covers the special case
-        //
-        // function () { let x; { var x; } }
-        //
-        // because the var declaration is hoisted to the function scope where
-        // 'x' is already bound.
-        DCHECK(IsDeclaredVariableMode(var->mode()));
-        // In harmony we treat re-declarations as early errors. See
-        // ES5 16 for a definition of early errors.
-        *ok = false;
-      }
-    } else if (mode == VariableMode::kVar) {
-      var->set_maybe_assigned();
+      var = DeclareLocal(name, mode, init);
+    }
+  } else {
+    var->set_maybe_assigned();
+    if (V8_UNLIKELY(IsLexicalVariableMode(mode) ||
+                    IsLexicalVariableMode(var->mode()))) {
+      // The name was declared in this scope before; check for conflicting
+      // re-declarations. We have a conflict if either of the declarations is
+      // not a var (in script scope, we also have to ignore legacy const for
+      // compatibility). There is similar code in runtime.cc in the Declare
+      // functions. The function CheckConflictingVarDeclarations checks for
+      // var and let bindings from different scopes whereas this is a check
+      // for conflicting declarations within the same scope. This check also
+      // covers the special case
+      //
+      // function () { let x; { var x; } }
+      //
+      // because the var declaration is hoisted to the function scope where
+      // 'x' is already bound.
+      //
+      // In harmony we treat re-declarations as early errors. See ES5 16 for a
+      // definition of early errors.
+      //
+      // Allow duplicate function decls for web compat, see bug 4693. If the
+      // duplication is allowed, then the var will show up in the
+      // SloppyBlockFunctionMap.
+      SloppyBlockFunctionMap* map =
+          GetDeclarationScope()->sloppy_block_function_map();
+      *ok =
+          map != nullptr && declaration->IsFunctionDeclaration() &&
+          declaration->AsFunctionDeclaration()
+              ->declares_sloppy_block_function() &&
+          map->Lookup(const_cast<AstRawString*>(name), name->Hash()) != nullptr;
+      *sloppy_mode_block_scope_function_redefinition = *ok;
     }
   }
   DCHECK_NOT_NULL(var);

src/ast/scopes.h

@@ -194,9 +194,7 @@ class V8_EXPORT_PRIVATE Scope : public NON_EXPORTED_BASE(ZoneObject) {
   // Declare a local variable in this scope. If the variable has been
   // declared before, the previously declared variable is returned.
   Variable* DeclareLocal(const AstRawString* name, VariableMode mode,
-                         InitializationFlag init_flag = kCreatedInitialized,
-                         VariableKind kind = NORMAL_VARIABLE,
-                         MaybeAssignedFlag maybe_assigned_flag = kNotAssigned);
+                         InitializationFlag init_flag = kCreatedInitialized);
 
   Variable* DeclareVariable(Declaration* declaration, VariableMode mode,
                             InitializationFlag init,

src/ast/variables.h

@@ -131,7 +131,6 @@ class Variable final : public ZoneObject {
     return kind() != SLOPPY_FUNCTION_NAME_VARIABLE || is_strict(language_mode);
   }
 
-  bool is_function() const { return kind() == FUNCTION_VARIABLE; }
   bool is_this() const { return kind() == THIS_VARIABLE; }
   bool is_sloppy_function_name() const {
     return kind() == SLOPPY_FUNCTION_NAME_VARIABLE;

src/globals.h

@@ -1030,7 +1030,6 @@ inline const char* VariableMode2String(VariableMode mode) {
 
 enum VariableKind : uint8_t {
   NORMAL_VARIABLE,
-  FUNCTION_VARIABLE,
   THIS_VARIABLE,
   SLOPPY_FUNCTION_NAME_VARIABLE
 };

src/parsing/parser.cc

@@ -1441,8 +1441,8 @@ Statement* Parser::DeclareFunction(const AstRawString* variable_name,
                                    ZonePtrList<const AstRawString>* names) {
   VariableProxy* proxy =
       factory()->NewVariableProxy(variable_name, NORMAL_VARIABLE, pos);
-  Declaration* declaration =
-      factory()->NewFunctionDeclaration(proxy, function, pos);
+  Declaration* declaration = factory()->NewFunctionDeclaration(
+      proxy, function, is_sloppy_block_function, pos);
   Declare(declaration, DeclarationDescriptor::NORMAL, mode,
           kCreatedInitialized);
   if (names) names->Add(variable_name, zone());

test/mjsunit/regress/regress-900786.js

@@ -0,0 +1,5 @@
+// Copyright 2018 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.
+
+assertThrows("{function g(){}function g(){+", SyntaxError);