[modules] Explicitly keep track of module requests.

src/ast/modules.h

Index: src/ast/modules.h
diff --git a/src/ast/modules.h b/src/ast/modules.h
index bdc31b24e630c288fc6eb1f732270797f85f7ee9..563c1259374d5f5188ccbaa89efef0558e8312a4 100644
--- a/src/ast/modules.h
+++ b/src/ast/modules.h
@@ -19,7 +19,8 @@ class ModuleInfoEntry;
 class ModuleDescriptor : public ZoneObject {
  public:
   explicit ModuleDescriptor(Zone* zone)
-      : special_exports_(1, zone),
+      : module_requests_(zone),
+        special_exports_(1, zone),
         special_imports_(1, zone),
         regular_exports_(zone),
         regular_imports_(zone) {}
@@ -78,7 +79,11 @@ class ModuleDescriptor : public ZoneObject {
     const AstRawString* export_name;
     const AstRawString* local_name;
     const AstRawString* import_name;
-    const AstRawString* module_request;
+    // The module_request value records the order in which modules are
+    // requested. It also functions as an index into the ModuleInfo's array of
+    // module specifiers and into the Module's array of requested modules.  A
+    // negative value means no module request.
+    int module_request;
 
     // TODO(neis): Remove local_name component?
     explicit Entry(Scanner::Location loc)
@@ -86,7 +91,7 @@ class ModuleDescriptor : public ZoneObject {
           export_name(nullptr),
           local_name(nullptr),
           import_name(nullptr),
-          module_request(nullptr) {}
+          module_request(-1) {}
 
     // (De-)serialization support.
     // Note that the location value is not preserved as it's only needed by the
@@ -96,6 +101,11 @@ class ModuleDescriptor : public ZoneObject {
                               Handle<ModuleInfoEntry> entry);
   };
 
+  // Module requests.
+  const ZoneMap<const AstRawString*, int>& module_requests() const {
+    return module_requests_;
+  }
+
   // Empty imports and namespace imports.
   const ZoneList<const Entry*>& special_imports() const {
     return special_imports_;
@@ -120,32 +130,34 @@ class ModuleDescriptor : public ZoneObject {
     DCHECK_NOT_NULL(entry->export_name);
     DCHECK_NOT_NULL(entry->local_name);
     DCHECK_NULL(entry->import_name);
+    DCHECK_LT(entry->module_request, 0);
     regular_exports_.insert(std::make_pair(entry->local_name, entry));
   }
 
   void AddSpecialExport(const Entry* entry, Zone* zone) {
-    DCHECK_NOT_NULL(entry->module_request);
+    DCHECK_LE(0, entry->module_request);
     special_exports_.Add(entry, zone);
   }
 
   void AddRegularImport(const Entry* entry) {
     DCHECK_NOT_NULL(entry->import_name);
     DCHECK_NOT_NULL(entry->local_name);
-    DCHECK_NOT_NULL(entry->module_request);
     DCHECK_NULL(entry->export_name);
+    DCHECK_LE(0, entry->module_request);
     regular_imports_.insert(std::make_pair(entry->local_name, entry));
     // We don't care if there's already an entry for this local name, as in that
     // case we will report an error when declaring the variable.
   }
 
   void AddSpecialImport(const Entry* entry, Zone* zone) {
-    DCHECK_NOT_NULL(entry->module_request);
     DCHECK_NULL(entry->export_name);
+    DCHECK_LE(0, entry->module_request);
     special_imports_.Add(entry, zone);
   }
 
  private:
   // TODO(neis): Use STL datastructure instead of ZoneList?
+  ZoneMap<const AstRawString*, int> module_requests_;
   ZoneList<const Entry*> special_exports_;
   ZoneList<const Entry*> special_imports_;
   ZoneMultimap<const AstRawString*, Entry*> regular_exports_;
@@ -172,6 +184,14 @@ class ModuleDescriptor : public ZoneObject {
   //   import {a as b} from "X"; export {a as c} from "X";
   // (The import entry is never deleted.)
   void MakeIndirectExportsExplicit(Zone* zone);
+
+  int AddModuleRequest(const AstRawString* specifier) {
+    DCHECK_NOT_NULL(specifier);
+    auto it = module_requests_
+                  .insert(std::make_pair(specifier, module_requests_.size()))
+                  .first;
+    return it->second;
+  }
 };
 
 }  // namespace internal