[parsing] Fix maybe-assigned flag in some cases.

This CL attempts to set the maybe-assigned flag for variables that are written
to as part of a destructuring or loop header.

For instance, in the following two cases we now mark x as maybe-assigned.

a) [x] = [1];
b) for (x of [1,2,3]) {};

There's more work to do here, this is just a first step.

R=adamk@chromium.org, mstarzinger@chromium.org
BUG=v8:5636

Review-Url: https://codereview.chromium.org/2562443003
Cr-Commit-Position: refs/heads/master@{#41582}

src/ast/ast.h

@@ -1634,8 +1634,10 @@ class VariableProxy final : public Expression {
 
   bool is_assigned() const { return IsAssignedField::decode(bit_field_); }
   void set_is_assigned() {
-    DCHECK(!is_resolved());
     bit_field_ = IsAssignedField::update(bit_field_, true);
+    if (is_resolved()) {
+      var()->set_maybe_assigned();
+    }
   }
 
   bool is_resolved() const { return IsResolvedField::decode(bit_field_); }
@@ -3455,9 +3457,13 @@ class AstNodeFactory final BASE_EMBEDDED {
                             Expression* value,
                             int pos) {
     DCHECK(Token::IsAssignmentOp(op));
+
+    if (op != Token::INIT && target->IsVariableProxy()) {
+      target->AsVariableProxy()->set_is_assigned();
+    }
+
     Assignment* assign = new (zone_) Assignment(op, target, value, pos);
     if (assign->is_compound()) {
-      DCHECK(Token::IsAssignmentOp(op));
       assign->binary_operation_ =
           NewBinaryOperation(assign->binary_op(), target, value, pos + 1);
     }

src/parsing/parser.cc

@@ -1909,6 +1909,7 @@ Statement* Parser::InitializeForEachStatement(ForEachStatement* stmt,
       body = block;
       each = factory()->NewVariableProxy(temp);
     }
+    MarkExpressionAsAssigned(each);
     stmt->AsForInStatement()->Initialize(each, subject, body);
   }
   return stmt;
@@ -2058,8 +2059,8 @@ Statement* Parser::InitializeForOfStatement(ForOfStatement* for_of,
   const int nopos = kNoSourcePosition;
   auto avfactory = ast_value_factory();
 
-  Variable* iterator = NewTemporary(ast_value_factory()->dot_iterator_string());
-  Variable* result = NewTemporary(ast_value_factory()->dot_result_string());
+  Variable* iterator = NewTemporary(avfactory->dot_iterator_string());
+  Variable* result = NewTemporary(avfactory->dot_result_string());
   Variable* completion = NewTemporary(avfactory->empty_string());
 
   // iterator = GetIterator(iterable)

src/parsing/pattern-rewriter.cc

@@ -219,6 +219,7 @@ void Parser::PatternRewriter::VisitVariableProxy(VariableProxy* pattern) {
     // But for var declarations we need to do a new lookup.
     if (descriptor_->mode == VAR) {
       proxy = var_init_scope->NewUnresolved(factory(), name);
+      // TODO(neis): Set is_assigned on proxy.
     } else {
       DCHECK_NOT_NULL(proxy);
       DCHECK_NOT_NULL(proxy->var());

test/cctest/test-parsing.cc

@@ -3273,6 +3273,7 @@ TEST(InnerAssignment) {
       {"var x = 5; function x() {}", true, false},
       {"var x = 4; var x = 5;", true, false},
       {"var [x, x] = [4, 5];", true, false},
+      {"var x; [x, x] = [4, 5];", true, false},
       {"var {a: x, b: x} = {a: 4, b: 5};", true, false},
       {"var x = {a: 4, b: (x = 5)};", true, false},
       {"var {x=1} = {a: 4, b: (x = 5)};", true, false},
@@ -3301,53 +3302,63 @@ TEST(InnerAssignment) {
       {"function x() {}; var x;", true, false},
       {"var x; try {} catch (x) { var x = 5; }", true, false},
   };
-  struct { const char* source; bool assigned; bool with; } inners[] = {
+  struct {
+    const char* source;
+    bool assigned;
+    bool with;
+  } inners[] = {
       // Actual assignments.
-    { "x = 1;", true, false },
-    { "x++;", true, false },
-    { "++x;", true, false },
-    { "x--;", true, false },
-    { "--x;", true, false },
-    { "{ x = 1; }", true, false },
-    { "'use strict'; { let x; }; x = 0;", true, false },
-    { "'use strict'; { const x = 1; }; x = 0;", true, false },
-    { "'use strict'; { function x() {} }; x = 0;", true, false },
-    { "with ({}) { x = 1; }", true, true },
-    { "eval('');", true, false },
-    { "'use strict'; { let y; eval('') }", true, false },
-    { "function h() { x = 0; }", true, false },
-    { "(function() { x = 0; })", true, false },
-    { "(function() { x = 0; })", true, false },
-    { "with ({}) (function() { x = 0; })", true, true },
+      {"x = 1;", true, false},
+      {"x++;", true, false},
+      {"++x;", true, false},
+      {"x--;", true, false},
+      {"--x;", true, false},
+      {"{ x = 1; }", true, false},
+      {"'use strict'; { let x; }; x = 0;", true, false},
+      {"'use strict'; { const x = 1; }; x = 0;", true, false},
+      {"'use strict'; { function x() {} }; x = 0;", true, false},
+      {"with ({}) { x = 1; }", true, true},
+      {"eval('');", true, false},
+      {"'use strict'; { let y; eval('') }", true, false},
+      {"function h() { x = 0; }", true, false},
+      {"(function() { x = 0; })", true, false},
+      {"(function() { x = 0; })", true, false},
+      {"with ({}) (function() { x = 0; })", true, true},
+      {"for (x of [1,2,3]) {}", true, false},
+      {"for (x in {a: 1}) {}", true, false},
+      {"for ([x] of [[1],[2],[3]]) {}", true, false},
+      {"for ([x] in {ab: 1}) {}", true, false},
+      {"for ([...x] in {ab: 1}) {}", true, false},
+      {"[x] = [1]", true, false},
       // Actual non-assignments.
-    { "", false, false },
-    { "x;", false, false },
-    { "var x;", false, false },
-    { "var x = 8;", false, false },
-    { "var x; x = 8;", false, false },
-    { "'use strict'; let x;", false, false },
-    { "'use strict'; let x = 8;", false, false },
-    { "'use strict'; let x; x = 8;", false, false },
-    { "'use strict'; const x = 8;", false, false },
-    { "function x() {}", false, false },
-    { "function x() { x = 0; }", false, false },
-    { "function h(x) { x = 0; }", false, false },
-    { "'use strict'; { let x; x = 0; }", false, false },
-    { "{ var x; }; x = 0;", false, false },
-    { "with ({}) {}", false, true },
-    { "var x; { with ({}) { x = 1; } }", false, true },
-    { "try {} catch(x) { x = 0; }", false, false },
-    { "try {} catch(x) { with ({}) { x = 1; } }", false, true },
+      {"", false, false},
+      {"x;", false, false},
+      {"var x;", false, false},
+      {"var x = 8;", false, false},
+      {"var x; x = 8;", false, false},
+      {"'use strict'; let x;", false, false},
+      {"'use strict'; let x = 8;", false, false},
+      {"'use strict'; let x; x = 8;", false, false},
+      {"'use strict'; const x = 8;", false, false},
+      {"function x() {}", false, false},
+      {"function x() { x = 0; }", false, false},
+      {"function h(x) { x = 0; }", false, false},
+      {"'use strict'; { let x; x = 0; }", false, false},
+      {"{ var x; }; x = 0;", false, false},
+      {"with ({}) {}", false, true},
+      {"var x; { with ({}) { x = 1; } }", false, true},
+      {"try {} catch(x) { x = 0; }", false, false},
+      {"try {} catch(x) { with ({}) { x = 1; } }", false, true},
       // Eval approximation.
-    { "eval('');", true, false },
-    { "function h() { eval(''); }", true, false },
-    { "(function() { eval(''); })", true, false },
+      {"eval('');", true, false},
+      {"function h() { eval(''); }", true, false},
+      {"(function() { eval(''); })", true, false},
       // Shadowing not recognized because of eval approximation.
-    { "var x; eval('');", true, false },
-    { "'use strict'; let x; eval('');", true, false },
-    { "try {} catch(x) { eval(''); }", true, false },
-    { "function x() { eval(''); }", true, false },
-    { "(function(x) { eval(''); })", true, false },
+      {"var x; eval('');", true, false},
+      {"'use strict'; let x; eval('');", true, false},
+      {"try {} catch(x) { eval(''); }", true, false},
+      {"function x() { eval(''); }", true, false},
+      {"(function(x) { eval(''); })", true, false},
   };
 
   int prefix_len = Utf8LengthHelper(prefix);
@@ -3410,7 +3421,7 @@ TEST(InnerAssignment) {
           // maybe_assigned.
           CHECK(is_maybe_assigned || (is_maybe_assigned == expected));
         } else {
-          CHECK(is_maybe_assigned == expected);
+          CHECK_EQ(is_maybe_assigned, expected);
         }
       }
     }