Stop treating finals as const

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 752 matching lines @@
         ((instantiator != NULL) && instantiator->is_captured())) {
       parsed_function->set_instantiator(
           new LoadLocalNode(node_sequence->token_pos(), instantiator));
     }
   }
 
   parsed_function->set_default_parameter_values(default_parameter_values);
 }
 
 
-// TODO(regis): Implement support for non-const final static fields (currently
-// supported "final" fields are actually const fields).
 // TODO(regis): Since a const variable is implicitly final,
 // rename ParseStaticConstGetter to ParseStaticFinalGetter and
 // rename kConstImplicitGetter to kImplicitFinalGetter.
 SequenceNode* Parser::ParseStaticConstGetter(const Function& func) {
   TRACE_PARSER("ParseStaticConstGetter");
   ParamList params;
   ASSERT(func.num_fixed_parameters() == 0);  // static.
   ASSERT(!func.HasOptionalParameters());
   ASSERT(AbstractType::Handle(func.result_type()).IsResolved());
 
   // Build local scope for function and populate with the formal parameters.
   OpenFunctionBlock(func);
   AddFormalParamsToScope(&params, current_block_->scope);
 
   const String& field_name = *ExpectIdentifier("field name expected");
   const Class& field_class = Class::Handle(func.Owner());
   const Field& field =
       Field::ZoneHandle(field_class.LookupStaticField(field_name));
 
   // Static const fields must have an initializer.
   ExpectToken(Token::kASSIGN);
 
   // We don't want to use ParseConstExpr() here because we don't want
   // the constant folding code to create, compile and execute a code
   // fragment to evaluate the expression. Instead, we just make sure
   // the static const field initializer is a constant expression and
   // leave the evaluation to the getter function.
   const intptr_t expr_pos = TokenPos();
   AstNode* expr = ParseExpr(kAllowConst, kConsumeCascades);
-  // TODO(hausner): Remove is_final check below once we support
-  // non-const finals.
-  if (field.is_const() || field.is_final()) {
+
+  if (field.is_const()) {
     // This getter will only be called once at compile time.
     if (expr->EvalConstExpr() == NULL) {
-      ErrorMsg(expr_pos, "initializer must be a compile time constant");
+      ErrorMsg(expr_pos, "initializer must be a compile-time constant");
     }
     ReturnNode* return_node = new ReturnNode(TokenPos(), expr);
     current_block_->statements->Add(return_node);
   } else {
     // This getter may be called each time the static field is accessed.
     // The following generated code lazily initializes the field:
     // if (field.value === transition_sentinel) {
     //   field.value = null;
     //   throw("circular dependency in field initialization");
     // }
     // if (field.value === sentinel) {
     //   field.value = transition_sentinel;
     //   field.value = expr;
     // }
     // return field.value;  // Type check is executed here in checked mode.
 
-    // TODO(regis): Remove this check once we support proper const fields.
-    if (expr->EvalConstExpr() == NULL) {
-      ErrorMsg(expr_pos, "initializer must be a compile time constant");
-    }
-
     // Generate code checking for circular dependency in field initialization.
     AstNode* compare_circular = new ComparisonNode(
         TokenPos(),
         Token::kEQ_STRICT,
         new LoadStaticFieldNode(TokenPos(), field),
         new LiteralNode(TokenPos(),
                         Instance::ZoneHandle(Object::transition_sentinel())));
     // Set field to null prior to throwing exception, so that subsequent
     // accesses to the field do not throw again, since initializers should only
     // be executed once.
@@ skipping 22 matching lines @@
         new LiteralNode(TokenPos(),
                         Instance::ZoneHandle(Object::sentinel())));
     SequenceNode* initialize_field = new SequenceNode(TokenPos(), NULL);
     initialize_field->Add(
         new StoreStaticFieldNode(
             TokenPos(),
             field,
             new LiteralNode(
                 TokenPos(),
                 Instance::ZoneHandle(Object::transition_sentinel()))));
+    // TODO(hausner): If evaluation of the field value throws an exception,
+    // we leave the field value as 'transition_sentinel', which is wrong.
+    // A second reference to the field later throws a circular dependency
+    // exception. The field should instead be set to null after an exception.

[regis, 2012/09/12 23:46:58]

This contradicts the comment on line 814 stating that the field is reset to null
before throwing.

[hausner, 2012/09/12 23:51:54]

No. The comment refers to the code under condition 'if (field.value ===
sentinel)'.

On 2012/09/12 23:46:58, regis wrote:

[regis, 2012/09/12 23:59:04]

I stand corrected :-)
Btw, there was an email discussion on this topic on Aug 15 entitled "lazy
initialization of finals".

     initialize_field->Add(new StoreStaticFieldNode(TokenPos(), field, expr));
     AstNode* uninitialized_check =
         new IfNode(TokenPos(), compare_uninitialized, initialize_field, NULL);
     current_block_->statements->Add(uninitialized_check);
 
     // Generate code returning the field value.
     ReturnNode* return_node =
         new ReturnNode(TokenPos(),
                        new LoadStaticFieldNode(TokenPos(), field));
     current_block_->statements->Add(return_node);
@@ skipping 1786 matching lines @@
       if (field->has_const || (field->has_static && field->has_final)) {
         ErrorMsg(field->name_pos,
                  "%s%s field '%s' must have an initializer expression",
                  field->has_static ? "static " : "",
                  field->has_const ? "const" : "final",
                  field->name->ToCString());
       }
     }
 
     // Create the field object.
-    // TODO(hausner): For now, all static final fields are constant. Remove
-    // this when lazy init of static variables is implemented.
     class_field = Field::New(*field->name,
                              field->has_static,
                              field->has_final,
-                             field->has_const || field->has_final,
+                             field->has_const,
                              current_class(),
                              field->name_pos);
     class_field.set_type(*field->type);
     class_field.set_has_initializer(has_initializer);
     members->AddField(class_field);
 
     // For static const fields, set value to "uninitialized" and
     // create a kConstImplicitGetter getter method.
     if (field->has_static && has_initializer) {
       class_field.set_value(init_value);
       if (!has_simple_literal) {
         String& getter_name = String::Handle(Field::GetterSymbol(*field->name));
         getter = Function::New(getter_name,
                                RawFunction::kConstImplicitGetter,
                                field->has_static,
-                               field->has_final,
+                               field->has_const,
                                /* is_abstract = */ false,
                                /* is_external = */ false,
                                current_class(),
                                field->name_pos);
         getter.set_result_type(*field->type);
         members->AddFunction(getter);
       }
     }
 
     // For instance fields, we create implicit getter and setter methods.
@@ skipping 347 matching lines @@
       ErrorMsg(classname_pos, "'%s' %s",
                class_name.ToCString(),
                is_patch ?
                    "interface cannot be patched" :
                    "is already defined as interface");
     } else if (is_patch) {
       String& patch = String::Handle(Symbols::New("patch "));
       patch = String::Concat(patch, class_name);
       patch = Symbols::New(patch);
       cls = Class::New(patch, script_, classname_pos);
-      cls.set_library(library_);
     } else {
       // Not patching a class, but it has been found. This must be one of the
       // pre-registered classes from object.cc or a duplicate definition.
       if (cls.functions() != Object::empty_array()) {
         ErrorMsg(classname_pos, "class '%s' is already defined",
                  class_name.ToCString());
       }
       // Pre-registered classes need their scripts connected at this time.
       cls.set_script(script_);
     }
@@ skipping 653 matching lines @@
     }
     AddInterfaceIfUnique(interfaces_pos, all_interfaces, interface);
   }
   cls_interfaces = Array::MakeArray(all_interfaces);
   cls.set_interfaces(cls_interfaces);
 }
 
 
 void Parser::ParseTopLevelVariable(TopLevel* top_level) {
   TRACE_PARSER("ParseTopLevelVariable");
-  const bool is_final = (CurrentToken() == Token::kFINAL);
   const bool is_const = (CurrentToken() == Token::kCONST);
+  // Const fields are implicitly final.
+  const bool is_final = is_const || (CurrentToken() == Token::kFINAL);
   const bool is_static = true;
   const AbstractType& type =
       AbstractType::ZoneHandle(ParseConstFinalVarOrType(
           FLAG_enable_type_checks ? ClassFinalizer::kTryResolve :
                                     ClassFinalizer::kIgnore));
   Field& field = Field::Handle();
   Function& getter = Function::Handle();
   while (true) {
     const intptr_t name_pos = TokenPos();
     String& var_name = *ExpectIdentifier("variable name expected");
 
     if (library_.LookupLocalObject(var_name) != Object::null()) {
       ErrorMsg(name_pos, "'%s' is already defined", var_name.ToCString());
     }
     String& accessor_name = String::Handle(Field::GetterName(var_name));
     if (library_.LookupLocalObject(accessor_name) != Object::null()) {
       ErrorMsg(name_pos, "getter for '%s' is already defined",
                var_name.ToCString());
     }
     accessor_name = Field::SetterName(var_name);
     if (library_.LookupLocalObject(accessor_name) != Object::null()) {
       ErrorMsg(name_pos, "setter for '%s' is already defined",
                var_name.ToCString());
     }
 
-    // TODO(hausner): const and final are equivalent at the moment.
-    field = Field::New(var_name,
-                       is_static,
-                       is_final || is_const,  // Const fields are also final.
-                       is_const || is_final,
-                       current_class(),
-                       name_pos);
+    field = Field::New(var_name, is_static, is_final, is_const,
+                       current_class(), name_pos);
     field.set_type(type);
     field.set_value(Instance::Handle(Instance::null()));
     top_level->fields.Add(field);
     library_.AddObject(field, var_name);
     if (CurrentToken() == Token::kASSIGN) {
       ConsumeToken();
       Instance& field_value = Instance::Handle(Object::sentinel());
       bool has_simple_literal = false;
-      if ((is_final || is_const) && (LookaheadToken(1) == Token::kSEMICOLON)) {
+      if (is_final && (LookaheadToken(1) == Token::kSEMICOLON)) {
         has_simple_literal = IsSimpleLiteral(type, &field_value);
       }
       SkipExpr();
       field.set_value(field_value);
       if (!has_simple_literal) {
         // Create a static const getter.
         String& getter_name = String::ZoneHandle(Field::GetterSymbol(var_name));
         getter = Function::New(getter_name,
                                RawFunction::kConstImplicitGetter,
                                is_static,
-                               is_final,
+                               is_const,
                                /* is_abstract = */ false,
                                /* is_external = */ false,
                                current_class(),
                                name_pos);
         getter.set_result_type(type);
         top_level->functions.Add(getter);
       }
-
-    } else if (is_final || is_const) {
+    } else if (is_final) {
       ErrorMsg(name_pos, "missing initializer for final or const variable");
     }
 
     if (CurrentToken() == Token::kCOMMA) {
       ConsumeToken();
     } else if (CurrentToken() == Token::kSEMICOLON) {
       ConsumeToken();
       break;
     } else {
       ExpectSemicolon();  // Reports error.
@@ skipping 2965 matching lines @@
 }
 
 
 // Evaluates the value of the compile time constant expression
 // and returns a literal node for the value.
 AstNode* Parser::FoldConstExpr(intptr_t expr_pos, AstNode* expr) {
   if (expr->IsLiteralNode()) {
     return expr;
   }
   if (expr->EvalConstExpr() == NULL) {
-    ErrorMsg(expr_pos, "expression must be a compile time constant");
+    ErrorMsg(expr_pos, "expression must be a compile-time constant");
   }
   return new LiteralNode(expr_pos, EvaluateConstExpr(expr));
 }
 
 
 // A compound assignment consists of a store and a load part. In order
 // to control inputs with potential side effects, the store part stores any
 // side effect creating inputs into locals. The load part reads then from
 // those locals. If expr may have side effects, it will be split into two new
 // left and right nodes. 'expr' becomes the right node, left node is returned as
@@ skipping 134 matching lines @@
       expr = FoldConstExpr(expr_pos, expr);
     }
     return expr;
   }
   // Assignment expressions.
   Token::Kind assignment_op = CurrentToken();
   const intptr_t assignment_pos = TokenPos();
   ConsumeToken();
   const intptr_t right_expr_pos = TokenPos();
   if (require_compiletime_const && (assignment_op != Token::kASSIGN)) {
-    ErrorMsg(right_expr_pos, "expression must be a compile time constant");
+    ErrorMsg(right_expr_pos, "expression must be a compile-time constant");
   }
   AstNode* right_expr = ParseExpr(require_compiletime_const, consume_cascades);
   AstNode* left_expr = expr;
   if (assignment_op != Token::kASSIGN) {
     // Compound assignment: store inputs with side effects into temp. locals.
     left_expr = PrepareCompoundAssignmentNodes(&expr);
   }
   right_expr =
       ExpandAssignableOp(assignment_pos, assignment_op, expr, right_expr);
   AstNode* assign_expr = CreateAssignmentNode(left_expr, right_expr);
@@ skipping 218 matching lines @@
                                            intptr_t ident_pos) {
   // If the static field has an initializer, initialize the field at compile
   // time, which is only possible if the field is const.
   AstNode* initializing_getter = RunStaticFieldInitializer(field);
   if (initializing_getter != NULL) {
     // The field is not yet initialized and could not be initialized at compile
     // time. The getter will initialize the field.
     return initializing_getter;
   }
   // The field is initialized.
-  // TODO(hausner): Remove the is_final check when we support non-const
-  // final static variables.
-  if (field.is_const() || field.is_final()) {
+  if (field.is_const()) {
     ASSERT(field.value() != Object::sentinel());
     ASSERT(field.value() != Object::transition_sentinel());
     return new LiteralNode(ident_pos, Instance::ZoneHandle(field.value()));
   }
   // Access the field directly.
   return new LoadStaticFieldNode(ident_pos, Field::ZoneHandle(field.raw()));
 }
 
 
 AstNode* Parser::ParseStaticFieldAccess(const Class& cls,
@@ skipping 548 matching lines @@
 }
 
 
 // If the field is already initialized, return no ast (NULL).
 // Otherwise, if the field is constant, initialize the field and return no ast.
 // If the field is not initialized and not const, return the ast for the getter.
 AstNode* Parser::RunStaticFieldInitializer(const Field& field) {
   ASSERT(field.is_static());
   const Instance& value = Instance::Handle(field.value());
   if (value.raw() == Object::transition_sentinel()) {
-    // TODO(hausner): Remove the check for is_final() once we support
-    // non-const final fields.
-    if (field.is_const() || field.is_final()) {
+    if (field.is_const()) {
       ErrorMsg("circular dependency while initializing static field '%s'",
                String::Handle(field.name()).ToCString());
     } else {
       // The implicit static getter will throw the exception if necessary.
       return new StaticGetterNode(TokenPos(),
                                   NULL,
                                   false,
                                   Class::ZoneHandle(field.owner()),
                                   String::ZoneHandle(field.name()));
     }
   } else if (value.raw() == Object::sentinel()) {
     // This field has not been referenced yet and thus the value has
     // not been evaluated. If the field is const, call the static getter method
     // to evaluate the expression and canonicalize the value.
-    // TODO(hausner): Remove the check for is_final() once we support
-    // non-const final fields.
-    if (field.is_const() || field.is_final()) {
+    if (field.is_const()) {
       field.set_value(Instance::Handle(Object::transition_sentinel()));
       const String& field_name = String::Handle(field.name());
       const String& getter_name =
           String::Handle(Field::GetterName(field_name));
       const Class& cls = Class::Handle(field.owner());
       GrowableArray<const Object*> arguments;  // no arguments.
       const int kNumArguments = 0;  // no arguments.
       const Array& kNoArgumentNames = Array::Handle();
       const Function& func =
           Function::Handle(Resolver::ResolveStatic(cls,
                                                    getter_name,
                                                    kNumArguments,
                                                    kNoArgumentNames,
                                                    Resolver::kIsQualified));
       ASSERT(!func.IsNull());
       ASSERT(func.kind() == RawFunction::kConstImplicitGetter);
       Object& const_value = Object::Handle(
           DartEntry::InvokeStatic(func, arguments, kNoArgumentNames));
       if (const_value.IsError()) {
         const Error& error = Error::Cast(const_value);
         if (error.IsUnhandledException()) {
           field.set_value(Instance::Handle());
           // It is a compile-time error if evaluation of a compile-time constant
           // would raise an exception.
           AppendErrorMsg(error, TokenPos(),
-                         "error initializing final field '%s'",
+                         "error initializing const field '%s'",
                          String::Handle(field.name()).ToCString());
         } else {
           Isolate::Current()->long_jump_base()->Jump(1, error);
         }
       }
       ASSERT(const_value.IsNull() || const_value.IsInstance());
       Instance& instance = Instance::Handle();
       instance ^= const_value.raw();
       if (!instance.IsNull()) {
         instance ^= instance.Canonicalize();
@@ skipping 749 matching lines @@
   // comma after the last entry.
   const String& dst_name = String::ZoneHandle(Symbols::ListLiteralElement());
   while (CurrentToken() != Token::kRBRACE) {
     AstNode* key = NULL;
     if (CurrentToken() == Token::kSTRING) {
       key = ParseStringLiteral();
     }
     if (key == NULL) {
       ErrorMsg("map entry key must be string literal");
     } else if (is_const && !key->IsLiteralNode()) {
-      ErrorMsg("map entry key must be compile time constant string");
+      ErrorMsg("map entry key must be compile-time constant string");
     }
     ExpectToken(Token::kCOLON);
     const bool saved_mode = SetAllowFunctionLiterals(true);
     const intptr_t value_pos = TokenPos();
     AstNode* value = ParseExpr(is_const, kConsumeCascades);
     SetAllowFunctionLiterals(saved_mode);
     if (FLAG_enable_type_checks &&
         !is_const &&
         !value_type.IsDynamicType()) {
       value = new AssignableNode(value_pos,
@@ skipping 976 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart