Add module alias map and underlying name to ModuleDecl

Author: elsh

include/swift/AST/Module.h

@@ -33,6 +33,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MD5.h"
 #include <set>
@@ -171,6 +172,12 @@ class ModuleDecl
   /// The ABI name of the module, if it differs from the module name.
   mutable Identifier ModuleABIName;
 
+  /// The underlying name for an alias used for this module (if any).
+  mutable Identifier ModuleUnderlyingName;
+  
+  /// Mapping between aliases and underlying names of imported or referenced modules
+  mutable llvm::DenseMap<Identifier, Identifier> ModuleAliasMap;
+
 public:
   /// Produces the components of a given module's full name in reverse order.
   ///
@@ -279,6 +286,9 @@ class ModuleDecl
 
   using Decl::getASTContext;
 
+  /// Retrieves the underlying module name given a module alias
+  Identifier lookupModuleAlias(Identifier key);
+  
   /// Retrieves information about which modules are implicitly imported by
   /// each file of this module.
   const ImplicitImportInfo &getImplicitImportInfo() const { return ImportInfo; }
@@ -357,6 +367,20 @@ class ModuleDecl
     ModuleABIName = name;
   }
 
+  /// Set the mapping between aliases and underlying names of imported or referenced modules
+  /// within this module.
+  void setModuleAliases(const llvm::StringMap<StringRef> &aliasMap);
+
+  /// If a module alias is used, set the corresponding underlying name.
+  /// It will be used for metadata and mangling.
+  void setUnderlyingName(Identifier name) {
+    ModuleUnderlyingName = name;
+  }
+
+  /// Retrieve the underlying name of the alias (if any) used for this module.
+  /// If no module alias is set, returns getName().
+  Identifier getUnderlyingName() const;
+
   /// User-defined module version number.
   llvm::VersionTuple UserModuleVersion;
   void setUserModuleVersion(llvm::VersionTuple UserVer) {
@@ -365,6 +389,7 @@ class ModuleDecl
   llvm::VersionTuple getUserModuleVersion() const {
     return UserModuleVersion;
   }
+
 private:
   /// A cache of this module's underlying module and required bystander if it's
   /// an underscored cross-import overlay.

lib/AST/Module.cpp

@@ -1564,6 +1564,28 @@ ImportedModule::removeDuplicates(SmallVectorImpl<ImportedModule> &imports) {
   imports.erase(last, imports.end());
 }
 
+void ModuleDecl::setModuleAliases(const llvm::StringMap<StringRef> &aliasMap) {
+  auto &ctx = getASTContext();
+  for (auto k: aliasMap.keys()) {
+    auto val = aliasMap.lookup(k);
+    ModuleAliasMap[ctx.getIdentifier(k)] = ctx.getIdentifier(val);
+  }
+}
+
+Identifier ModuleDecl::lookupModuleAlias(Identifier key) {
+  auto found = ModuleAliasMap.find(key);
+  if (found != ModuleAliasMap.end()) {
+    return found->second;
+  }
+  return Identifier();
+}
+
+Identifier ModuleDecl::getUnderlyingName() const {
+    if (!ModuleUnderlyingName.empty())
+        return ModuleUnderlyingName;
+    return getName();
+}
+
 Identifier ModuleDecl::getABIName() const {
   if (!ModuleABIName.empty())
     return ModuleABIName;

lib/Frontend/Frontend.cpp

@@ -969,6 +969,8 @@ ModuleDecl *CompilerInstance::getMainModule() const {
       MainModule->setABIName(getASTContext().getIdentifier(
           Invocation.getFrontendOptions().ModuleABIName));
     }
+    if (!Invocation.getFrontendOptions().ModuleAliasMap.empty())
+      MainModule->setModuleAliases(Invocation.getFrontendOptions().ModuleAliasMap);
     if (Invocation.getFrontendOptions().EnableLibraryEvolution)
       MainModule->setResilienceStrategy(ResilienceStrategy::Resilient);
     if (Invocation.getLangOptions().WarnConcurrency ||