[modules] Detect all indirect exports and represent them as such.

src/ast/modules.h

Index: src/ast/modules.h
diff --git a/src/ast/modules.h b/src/ast/modules.h
index 4c63df9dfad2569125bb34b3fa309c0f03f0430b..5f63fce26955249ef7303f6b1e037ade1efa29d7 100644
--- a/src/ast/modules.h
+++ b/src/ast/modules.h
@@ -63,9 +63,9 @@ class ModuleDescriptor : public ZoneObject {
     Zone* zone);
 
   // Check if module is well-formed and report error if not.
+  // Also canonicalize indirect exports.
   bool Validate(DeclarationScope* module_scope,
-                PendingCompilationErrorHandler* error_handler,
-                Zone* zone) const;
+                PendingCompilationErrorHandler* error_handler, Zone* zone);
 
   struct ModuleEntry : public ZoneObject {
     const Scanner::Location location;
@@ -82,7 +82,7 @@ class ModuleDescriptor : public ZoneObject {
           module_request(nullptr) {}
   };
 
-  const ZoneList<const ModuleEntry*>& exports() const { return exports_; }
+  const ZoneList<ModuleEntry*>& exports() const { return exports_; }
 
   // Empty imports and namespace imports.
   const ZoneList<const ModuleEntry*>& special_imports() const {
@@ -96,9 +96,27 @@ class ModuleDescriptor : public ZoneObject {
   }
 
  private:
-  ZoneList<const ModuleEntry*> exports_;
+  ZoneList<ModuleEntry*> exports_;
   ZoneList<const ModuleEntry*> special_imports_;
   ZoneMap<const AstRawString*, const ModuleEntry*> regular_imports_;
+
+  // Find any implicitly indirect exports and make them explicit.
+  //
+  // An explicitly indirect export is an export entry arising from an export
+  // statement of the following form:
+  //   export {a as c} from "X";
+  // An implicitly indirect export corresponds to
+  //   export {b as c};
+  // in the presence of an import statement of the form
+  //   import {a as b} from "X";
+  // This function finds such implicitly indirect export entries and rewrites
+  // them by filling in the import name and module request, as well as nulling
+  // out the local name.  Effectively, it turns
+  //   import {a as b} from "X"; export {b as c};
+  // into:
+  //   import {a as b} from "X"; export {a as c} from "X";
+  // (The import entry is never deleted.)
+  void MakeIndirectExportsExplicit();
 };
 
 }  // namespace internal