Add a mode to completely deserialize scope chains

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 603b6c8a33cc78ddbd753511bf0661fe29536845..bdfa4344c2fa929c4ed71d23502b27e97f854f70 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -942,22 +942,27 @@ FunctionLiteral* Parser::DoParseProgram(ParseInfo* info) {
 
   FunctionLiteral* result = NULL;
   {
-    // TODO(wingo): Add an outer SCRIPT_SCOPE corresponding to the native
-    // context, which will have the "this" binding for script scopes.
-    Scope* scope = NewScriptScope();
-    info->set_script_scope(scope);
-    if (!info->context().is_null() && !info->context()->IsNativeContext()) {
-      scope = Scope::DeserializeScopeChain(info->isolate(), zone(),
-                                           *info->context(), scope,
-                                           ast_value_factory());
-      // The Scope is backed up by ScopeInfo (which is in the V8 heap); this
-      // means the Parser cannot operate independent of the V8 heap. Tell the
-      // string table to internalize strings and values right after they're
-      // created. This kind of parsing can only be done in the main thread.
-      DCHECK(parsing_on_main_thread_);
-      ast_value_factory()->Internalize(info->isolate());
+    Scope* scope;
+    if (info->script_scope()) {

[marja, 2016/08/03 08:07:48]

"script_scope" as a name is very generic, could something like
"deserialized_scope" be clearer? (No, that's not a really good name either, but
something... outer? Lazy?)

Somebody reading only this file is not at all in the mental context of scope
deserialization, so it's hard to understand when do we have a script_scope and
when not (doesn't each script have a scope...).

[jochen (gone - plz use gerrit), 2016/08/03 09:14:49]

well, it's corresponding to the existing set_script_scope()

+      scope = info->script_scope();
+    } else {
+      // TODO(wingo): Add an outer SCRIPT_SCOPE corresponding to the native
+      // context, which will have the "this" binding for script scopes.
+      scope = NewScriptScope();
+      info->set_script_scope(scope);
+      if (!info->context().is_null() && !info->context()->IsNativeContext()) {
+        scope = Scope::DeserializeScopeChain(
+            info->isolate(), zone(), *info->context(), scope,
+            ast_value_factory(), Scope::DeserializationMode::kKeepScopeInfo);
+        // The Scope is backed up by ScopeInfo (which is in the V8 heap); this
+        // means the Parser cannot operate independent of the V8 heap. Tell the
+        // string table to internalize strings and values right after they're
+        // created. This kind of parsing can only be done in the main thread.
+        DCHECK(parsing_on_main_thread_);
+        ast_value_factory()->Internalize(info->isolate());
+      }
+      original_scope_ = scope;
     }
-    original_scope_ = scope;
     if (info->is_eval()) {
       if (!scope->is_script_scope() || is_strict(info->language_mode())) {
         parsing_mode = PARSE_EAGERLY;
@@ -1116,8 +1121,9 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
       // Ok to use Isolate here, since lazy function parsing is only done in the
       // main thread.
       DCHECK(parsing_on_main_thread_);
-      scope = Scope::DeserializeScopeChain(isolate, zone(), *info->context(),
-                                           scope, ast_value_factory());
+      scope = Scope::DeserializeScopeChain(
+          isolate, zone(), *info->context(), scope, ast_value_factory(),
+          Scope::DeserializationMode::kKeepScopeInfo);
     }
     original_scope_ = scope;
     FunctionState function_state(&function_state_, &scope_state_, scope,