[Frontend] Move initial REPL file creation logic

Move the logic out of the frontend and into its
only client, swift-ide-test.

Author: hamishknight

lib/Frontend/Frontend.cpp

@@ -779,15 +779,6 @@ void CompilerInstance::performSemaUpTo(SourceFile::ASTStage_t LimitStage) {
   // references, this can be removed.
   (void)MainModule->getImplicitImports();
 
-  if (Invocation.getInputKind() == InputFileKind::SwiftREPL) {
-    // Create the initial empty REPL file. This only exists to feed in the
-    // implicit imports such as the standard library.
-    auto *replFile =
-        createSourceFileForMainModule(SourceFileKind::Main, /*BufferID*/ None);
-    performImportResolution(*replFile);
-    return;
-  }
-
   // Make sure the main file is the first file in the module, so do this now.
   if (MainBufferID != NO_SUCH_BUFFER) {
     (void)createSourceFileForMainModule(Invocation.getSourceFileKind(),

tools/swift-ide-test/swift-ide-test.cpp

@@ -897,13 +897,21 @@ static int doREPLCodeCompletion(const CompilerInvocation &InitInvok,
   CI.addDiagnosticConsumer(&PrintDiags);
   if (CI.setup(Invocation))
     return 1;
-  registerIDERequestFunctions(CI.getASTContext().evaluator);
-  CI.performSema();
-
-  SourceFile &SF = CI.getMainModule()->getMainSourceFile(SourceFileKind::Main);
+  auto &ctx = CI.getASTContext();
+  registerIDERequestFunctions(ctx.evaluator);
+
+  // Create an initial empty SourceFile. This only exists to feed in the
+  // implicit stdlib import.
+  ImplicitImportInfo importInfo;
+  importInfo.StdlibKind = ImplicitStdlibKind::Stdlib;
+  auto *M = ModuleDecl::create(ctx.getIdentifier(Invocation.getModuleName()),
+                               ctx, importInfo);
+  auto *SF = new (ctx) SourceFile(*M, SourceFileKind::Main, /*BufferID*/ None);
+  M->addFile(*SF);
+  performImportResolution(*SF);
 
   REPLCompletions REPLCompl;
-  REPLCompl.populate(SF, BufferText);
+  REPLCompl.populate(*SF, BufferText);
   llvm::outs() << "Begin completions\n";
   for (StringRef S : REPLCompl.getCompletionList()) {
     llvm::outs() << S << "\n";