[AST] Remove SourceFile::addImports

Temporarily replace with `SourceFile::setImports`
until import resolution is requestified. Now
imports are only set once for a given SourceFile.

Because we're now asserting in more places that
import resolution must have run before querying
imports, this commit also adds
`getCachedUnderlyingType` to TypeAliasDecl to stop
the ASTDumper from trying to query imports for a
-dump-parse invocation.

include/swift/AST/Decl.h

@@ -3032,6 +3032,10 @@ public:
   Type getUnderlyingType() const;
   void setUnderlyingType(Type type);
 
+  /// Returns the interface type of the underlying type if computed, null
+  /// otherwise. Should only be used for dumping.
+  Type getCachedUnderlyingType() const { return UnderlyingTy.getType(); }
+
   /// For generic typealiases, return the unbound generic type.
   UnboundGenericType *getUnboundGenericType() const;
 

include/swift/AST/SourceFile.h

@@ -121,8 +121,8 @@ private:
 
   /// This is the list of modules that are imported by this module.
   ///
-  /// This is filled in by the import resolution phase.
-  ArrayRef<ImportedModuleDesc> Imports;
+  /// This is \c None until it is filled in by the import resolution phase.
+  Optional<ArrayRef<ImportedModuleDesc>> Imports;
 
   /// A unique identifier representing this file; used to mark private decls
   /// within the file to keep them from conflicting with other files in the
@@ -333,7 +333,9 @@ public:
 
   ~SourceFile();
 
-  void addImports(ArrayRef<ImportedModuleDesc> IM);
+  /// Set the imports for this source file. This gets called by import
+  /// resolution.
+  void setImports(ArrayRef<ImportedModuleDesc> imports);
 
   enum ImportQueryKind {
     /// Return the results for testable or private imports.

lib/AST/ASTDumper.cpp

@@ -631,7 +631,7 @@ namespace {
     void visitTypeAliasDecl(TypeAliasDecl *TAD) {
       printCommon(TAD, "typealias");
       PrintWithColorRAII(OS, TypeColor) << " type='";
-      if (auto underlying = TAD->getUnderlyingType()) {
+      if (auto underlying = TAD->getCachedUnderlyingType()) {
         PrintWithColorRAII(OS, TypeColor)
           << underlying.getString();
       } else {

lib/AST/Module.cpp

@@ -1103,7 +1103,7 @@ public:
   /// Only intended for use by lookupOperatorDeclForName.
   static ArrayRef<SourceFile::ImportedModuleDesc>
   getImportsForSourceFile(const SourceFile &SF) {
-    return SF.Imports;
+    return *SF.Imports;
   }
 };
 
@@ -1408,7 +1408,10 @@ SourceFile::getImportedModules(SmallVectorImpl<ModuleDecl::ImportedModule> &modu
   // We currently handle this for a direct import from the overlay, but not when
   // it happens through other imports.
   assert(filter && "no imports requested?");
-  for (auto desc : Imports) {
+  if (!Imports)
+    return;
+
+  for (auto desc : *Imports) {
     ModuleDecl::ImportFilter requiredFilter;
     if (desc.importOptions.contains(ImportFlags::Exported))
       requiredFilter |= ModuleDecl::ImportFilterKind::Public;
@@ -2036,23 +2039,14 @@ void SourceFile::print(ASTPrinter &Printer, const PrintOptions &PO) {
   }
 }
 
-void SourceFile::addImports(ArrayRef<ImportedModuleDesc> IM) {
-  if (IM.empty())
-    return;
-  ASTContext &ctx = getASTContext();
-  auto newBuf =
-      ctx.AllocateUninitialized<ImportedModuleDesc>(Imports.size() + IM.size());
-
-  auto iter = newBuf.begin();
-  iter = std::uninitialized_copy(Imports.begin(), Imports.end(), iter);
-  iter = std::uninitialized_copy(IM.begin(), IM.end(), iter);
-  assert(iter == newBuf.end());
-
-  Imports = newBuf;
+void SourceFile::setImports(ArrayRef<ImportedModuleDesc> imports) {
+  assert(!Imports && "Already computed imports");
+  Imports = getASTContext().AllocateCopy(imports);
 
   // Update the HasImplementationOnlyImports flag.
+  // TODO: Requestify this.
   if (!HasImplementationOnlyImports) {
-    for (auto &desc : IM) {
+    for (auto &desc : imports) {
       if (desc.importOptions.contains(ImportFlags::ImplementationOnly))
         HasImplementationOnlyImports = true;
     }
@@ -2070,7 +2064,7 @@ bool SourceFile::hasTestableOrPrivateImport(
     // filename does not need to match (and we don't serialize it for such
     // decls).
     return std::any_of(
-        Imports.begin(), Imports.end(),
+        Imports->begin(), Imports->end(),
         [module, queryKind](ImportedModuleDesc desc) -> bool {
           if (queryKind == ImportQueryKind::TestableAndPrivate)
             return desc.module.second == module &&
@@ -2112,7 +2106,7 @@ bool SourceFile::hasTestableOrPrivateImport(
   if (filename.empty())
     return false;
 
-  return std::any_of(Imports.begin(), Imports.end(),
+  return std::any_of(Imports->begin(), Imports->end(),
                      [module, filename](ImportedModuleDesc desc) -> bool {
                        return desc.module.second == module &&
                               desc.importOptions.contains(
@@ -2130,7 +2124,7 @@ bool SourceFile::isImportedImplementationOnly(const ModuleDecl *module) const {
   auto &imports = getASTContext().getImportCache();
 
   // Look at the imports of this source file.
-  for (auto &desc : Imports) {
+  for (auto &desc : *Imports) {
     // Ignore implementation-only imports.
     if (desc.importOptions.contains(ImportFlags::ImplementationOnly))
       continue;
@@ -2147,7 +2141,7 @@ bool SourceFile::isImportedImplementationOnly(const ModuleDecl *module) const {
 
 void SourceFile::lookupImportedSPIGroups(const ModuleDecl *importedModule,
                                     SmallVectorImpl<Identifier> &spiGroups) const {
-  for (auto &import : Imports) {
+  for (auto &import : *Imports) {
     if (import.importOptions.contains(ImportFlags::SPIAccessControl) &&
         importedModule == std::get<ModuleDecl*>(import.module)) {
       auto importedSpis = import.spiGroups;

lib/Sema/ImportResolution.cpp

@@ -288,7 +288,7 @@ void swift::performImportResolution(SourceFile &SF) {
   for (auto D : SF.getTopLevelDecls())
     resolver.visit(D);
 
-  SF.addImports(resolver.getFinishedImports());
+  SF.setImports(resolver.getFinishedImports());
 
   SF.ASTStage = SourceFile::ImportsResolved;
   verify(SF);