[destructuring] Implement basic binding destructuring infrastructure

src/pattern-rewriter.cc

+// Copyright 2015 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.
+
+#include "src/ast.h"
+#include "src/parser.h"
+#include "src/pattern-rewriter.h"
+
+namespace v8 {
+
+namespace internal {
+
+
+bool Parser::PatternRewriter::IsSingleVariableBinding() const {
+  return pattern_->IsVariableProxy();
+}
+
+
+const AstRawString* Parser::PatternRewriter::SingleName() const {
+  DCHECK(IsSingleVariableBinding());
+  return pattern_->AsVariableProxy()->raw_name();
+}
+
+
+void Parser::PatternRewriter::DeclareAndInitializeVariables(Expression* value,
+                                                            int* nvars,
+                                                            bool* ok) {
+  ok_ = ok;
+  nvars_ = nvars;
+  RecurseIntoSubpattern(pattern_, value);
+  ok_ = nullptr;
+  nvars_ = nullptr;
+}
+
+
+void Parser::PatternRewriter::VisitVariableProxy(VariableProxy* pattern) {
+  Expression* value = current_value_;
+  decl_->scope->RemoveUnresolved(pattern->AsVariableProxy());
+
+  // Declare variable.
+  // Note that we *always* must treat the initial value via a separate init
+  // assignment for variables and constants because the value must be assigned
+  // when the variable is encountered in the source. But the variable/constant
+  // is declared (and set to 'undefined') upon entering the function within
+  // which the variable or constant is declared. Only function variables have
+  // an initial value in the declaration (because they are initialized upon
+  // entering the function).
+  //
+  // If we have a legacy const declaration, in an inner scope, the proxy
+  // is always bound to the declared variable (independent of possibly
+  // surrounding 'with' statements).
+  // For let/const declarations in harmony mode, we can also immediately
+  // pre-resolve the proxy because it resides in the same scope as the
+  // declaration.
+  Parser* parser = decl_->parser;
+  const AstRawString* name = pattern->raw_name();
+  VariableProxy* proxy = parser->NewUnresolved(name, decl_->mode);
+  Declaration* declaration = factory()->NewVariableDeclaration(
+      proxy, decl_->mode, decl_->scope, decl_->pos);
+  Variable* var = parser->Declare(declaration, decl_->mode != VAR, ok_);
+  if (!*ok_) return;
+  DCHECK_NOT_NULL(var);
+  DCHECK(!proxy->is_resolved() || proxy->var() == var);
+  var->set_initializer_position(decl_->initializer_position);
+  (*nvars_)++;
+  if (decl_->declaration_scope->num_var_or_const() > kMaxNumFunctionLocals) {
+    parser->ReportMessage("too_many_variables");
+    *ok_ = false;
+    return;
+  }
+  if (decl_->names) {
+    decl_->names->Add(name, zone());
+  }
+
+  // Initialize variables if needed. A
+  // declaration of the form:
+  //
+  //    var v = x;
+  //
+  // is syntactic sugar for:
+  //
+  //    var v; v = x;
+  //
+  // In particular, we need to re-lookup 'v' (in scope_, not
+  // declaration_scope) as it may be a different 'v' than the 'v' in the
+  // declaration (e.g., if we are inside a 'with' statement or 'catch'
+  // block).
+  //
+  // However, note that const declarations are different! A const
+  // declaration of the form:
+  //
+  //   const c = x;
+  //
+  // is *not* syntactic sugar for:
+  //
+  //   const c; c = x;
+  //
+  // The "variable" c initialized to x is the same as the declared
+  // one - there is no re-lookup (see the last parameter of the
+  // Declare() call above).
+  Scope* initialization_scope =
+      decl_->is_const ? decl_->declaration_scope : decl_->scope;
+
+
+  // Global variable declarations must be compiled in a specific
+  // way. When the script containing the global variable declaration
+  // is entered, the global variable must be declared, so that if it
+  // doesn't exist (on the global object itself, see ES5 errata) it
+  // gets created with an initial undefined value. This is handled
+  // by the declarations part of the function representing the
+  // top-level global code; see Runtime::DeclareGlobalVariable. If
+  // it already exists (in the object or in a prototype), it is
+  // *not* touched until the variable declaration statement is
+  // executed.
+  //
+  // Executing the variable declaration statement will always
+  // guarantee to give the global object an own property.
+  // This way, global variable declarations can shadow
+  // properties in the prototype chain, but only after the variable
+  // declaration statement has been executed. This is important in
+  // browsers where the global object (window) has lots of
+  // properties defined in prototype objects.
+  if (initialization_scope->is_script_scope() &&
+      !IsLexicalVariableMode(decl_->mode)) {
+    // Compute the arguments for the runtime
+    // call.test-parsing/InitializedDeclarationsInStrictForOfError
+    ZoneList<Expression*>* arguments =
+        new (zone()) ZoneList<Expression*>(3, zone());
+    // We have at least 1 parameter.
+    arguments->Add(factory()->NewStringLiteral(name, decl_->pos), zone());
+    CallRuntime* initialize;
+
+    if (decl_->is_const) {
+      arguments->Add(value, zone());
+      value = NULL;  // zap the value to avoid the unnecessary assignment
+
+      // Construct the call to Runtime_InitializeConstGlobal
+      // and add it to the initialization statement block.
+      // Note that the function does different things depending on
+      // the number of arguments (1 or 2).
+      initialize = factory()->NewCallRuntime(
+          ast_value_factory()->initialize_const_global_string(),
+          Runtime::FunctionForId(Runtime::kInitializeConstGlobal), arguments,
+          decl_->pos);
+    } else {
+      // Add language mode.
+      // We may want to pass singleton to avoid Literal allocations.
+      LanguageMode language_mode = initialization_scope->language_mode();
+      arguments->Add(factory()->NewNumberLiteral(language_mode, decl_->pos),
+                     zone());
+
+      // Be careful not to assign a value to the global variable if
+      // we're in a with. The initialization value should not
+      // necessarily be stored in the global object in that case,
+      // which is why we need to generate a separate assignment node.
+      if (value != NULL && !inside_with()) {
+        arguments->Add(value, zone());
+        value = NULL;  // zap the value to avoid the unnecessary assignment
+        // Construct the call to Runtime_InitializeVarGlobal
+        // and add it to the initialization statement block.
+        initialize = factory()->NewCallRuntime(
+            ast_value_factory()->initialize_var_global_string(),
+            Runtime::FunctionForId(Runtime::kInitializeVarGlobal), arguments,
+            decl_->pos);
+      } else {
+        initialize = NULL;
+      }
+    }
+
+    if (initialize != NULL) {
+      decl_->block->AddStatement(
+          factory()->NewExpressionStatement(initialize, RelocInfo::kNoPosition),
+          zone());
+    }
+  } else if (decl_->needs_init) {
+    // Constant initializations always assign to the declared constant which
+    // is always at the function scope level. This is only relevant for
+    // dynamically looked-up variables and constants (the
+    // start context for constant lookups is always the function context,
+    // while it is the top context for var declared variables). Sigh...
+    // For 'let' and 'const' declared variables in harmony mode the
+    // initialization also always assigns to the declared variable.
+    DCHECK_NOT_NULL(proxy);
+    DCHECK_NOT_NULL(proxy->var());
+    DCHECK_NOT_NULL(value);
+    Assignment* assignment =
+        factory()->NewAssignment(decl_->init_op, proxy, value, decl_->pos);
+    decl_->block->AddStatement(
+        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+        zone());
+    value = NULL;
+  }
+
+  // Add an assignment node to the initialization statement block if we still
+  // have a pending initialization value.
+  if (value != NULL) {
+    DCHECK(decl_->mode == VAR);
+    // 'var' initializations are simply assignments (with all the consequences
+    // if they are inside a 'with' statement - they may change a 'with' object
+    // property).
+    VariableProxy* proxy = initialization_scope->NewUnresolved(factory(), name);
+    Assignment* assignment =
+        factory()->NewAssignment(decl_->init_op, proxy, value, decl_->pos);
+    decl_->block->AddStatement(
+        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+        zone());
+  }
+}
+
+
+void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern) {
+  auto temp = decl_->declaration_scope->NewTemporary(
+      ast_value_factory()->empty_string());
+  auto assignment =
+      factory()->NewAssignment(Token::ASSIGN, factory()->NewVariableProxy(temp),
+                               current_value_, RelocInfo::kNoPosition);
+  decl_->block->AddStatement(
+      factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+      zone());
+  for (ObjectLiteralProperty* property : *pattern->properties()) {
+    // TODO(dslomov): computed property names.
+    RecurseIntoSubpattern(
+        property->value(),
+        factory()->NewProperty(factory()->NewVariableProxy(temp),
+                               property->key(), RelocInfo::kNoPosition));
+  }
+}
+
+
+void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node) {
+  // TODO(dslomov): implement.
+}
+
+
+void Parser::PatternRewriter::VisitAssignment(Assignment* node) {
+  // TODO(dslomov): implement.
+}
+
+
+void Parser::PatternRewriter::VisitSpread(Spread* node) {
+  // TODO(dslomov): implement.
+}
+
+
+// =============== UNREACHABLE =============================
+
+void Parser::PatternRewriter::Visit(AstNode* node) { UNREACHABLE(); }
+
+#define NOT_A_PATTERN(Node)                                        \
+  void Parser::PatternRewriter::Visit##Node(v8::internal::Node*) { \
+    UNREACHABLE();                                                 \
+  }
+
+NOT_A_PATTERN(BinaryOperation)
+NOT_A_PATTERN(Block)
+NOT_A_PATTERN(BreakStatement)
+NOT_A_PATTERN(Call)
+NOT_A_PATTERN(CallNew)
+NOT_A_PATTERN(CallRuntime)
+NOT_A_PATTERN(CaseClause)
+NOT_A_PATTERN(ClassLiteral)
+NOT_A_PATTERN(CompareOperation)
+NOT_A_PATTERN(Conditional)
+NOT_A_PATTERN(ContinueStatement)
+NOT_A_PATTERN(CountOperation)
+NOT_A_PATTERN(DebuggerStatement)
+NOT_A_PATTERN(DoWhileStatement)
+NOT_A_PATTERN(EmptyStatement)
+NOT_A_PATTERN(ExportDeclaration)
+NOT_A_PATTERN(ExpressionStatement)
+NOT_A_PATTERN(ForInStatement)
+NOT_A_PATTERN(ForOfStatement)
+NOT_A_PATTERN(ForStatement)
+NOT_A_PATTERN(FunctionDeclaration)
+NOT_A_PATTERN(FunctionLiteral)
+NOT_A_PATTERN(IfStatement)
+NOT_A_PATTERN(ImportDeclaration)
+NOT_A_PATTERN(Literal)
+NOT_A_PATTERN(NativeFunctionLiteral)
+NOT_A_PATTERN(Property)
+NOT_A_PATTERN(RegExpLiteral)
+NOT_A_PATTERN(ReturnStatement)
+NOT_A_PATTERN(SuperReference)
+NOT_A_PATTERN(SwitchStatement)
+NOT_A_PATTERN(ThisFunction)
+NOT_A_PATTERN(Throw)
+NOT_A_PATTERN(TryCatchStatement)
+NOT_A_PATTERN(TryFinallyStatement)
+NOT_A_PATTERN(UnaryOperation)
+NOT_A_PATTERN(VariableDeclaration)
+NOT_A_PATTERN(WhileStatement)
+NOT_A_PATTERN(WithStatement)
+NOT_A_PATTERN(Yield)
+
+#undef NOT_A_PATTERN
+}
+}  // namespace v8::internal