Taking Jordan's suggestions.

Author: David Ungar

include/swift/Frontend/FrontendOptions.h

@@ -548,7 +548,7 @@ class FrontendOptions {
 
   static bool doesActionProduceOutput(ActionType);
   static bool doesActionProduceTextualOutput(ActionType);
-  static bool doesActionImplyMainModule(ActionType);
+  static bool needsProperModuleName(ActionType);
 };
 
 }

lib/Frontend/CompilerInvocation.cpp

@@ -640,7 +640,7 @@ bool FrontendArgsToOptionsConverter::computeModuleName() {
       (Opts.ModuleName != STDLIB_NAME || Opts.ParseStdlib)) {
     return false;
   }
-  if (FrontendOptions::doesActionImplyMainModule(Opts.RequestedAction) ||
+  if (!FrontendOptions::needsProperModuleName(Opts.RequestedAction) ||
       Opts.isCompilingExactlyOneSwiftFile()) {
     Opts.ModuleName = "main";
     return false;
@@ -681,8 +681,9 @@ bool FrontendArgsToOptionsConverter::computeFallbackModuleName() {
 }
 
 bool FrontendArgsToOptionsConverter::computeOutputFilenames() {
+  assert(Opts.OutputFilenames.empty() &&
+         "Output filename should not be set at this point");
   if (!FrontendOptions::doesActionProduceOutput(Opts.RequestedAction)) {
-    Opts.OutputFilenames.clear();
     return false;
   }
   ArrayRef<std::string> outputFilenamesFromCommandLineOrFilelist =

lib/Frontend/FrontendOptions.cpp

@@ -96,7 +96,7 @@ void FrontendInputs::transformInputFilenames(
   }
 }
 
-bool FrontendOptions::doesActionImplyMainModule(ActionType action) {
+bool FrontendOptions::needsProperModuleName(ActionType action) {
   switch (action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
@@ -108,24 +108,24 @@ bool FrontendOptions::doesActionImplyMainModule(ActionType action) {
   case ActionType::PrintAST:
   case ActionType::DumpScopeMaps:
   case ActionType::DumpTypeRefinementContexts:
-    return true;
+    return false;
   case ActionType::EmitPCH:
   case ActionType::EmitSILGen:
   case ActionType::EmitSIL:
   case ActionType::EmitSIBGen:
   case ActionType::EmitSIB:
   case ActionType::EmitModuleOnly:
   case ActionType::MergeModules:
-    return false;
+    return true;
   case ActionType::Immediate:
   case ActionType::REPL:
-    return true;
+    return false;
   case ActionType::EmitAssembly:
   case ActionType::EmitIR:
   case ActionType::EmitBC:
   case ActionType::EmitObject:
   case ActionType::EmitImportedModules:
-    return false;
+    return true;
   }
   llvm_unreachable("Unknown ActionType");
 }

test/Frontend/immediate-mode-no-output.swift

@@ -1 +1,3 @@
-// RUN: rm -rf %t &&  mkdir -p %t && cd %t && echo >test.swift && %swift  -interpret test.swift &&  rm test.swift && test `ls | wc -w` -eq 0
+// RUN: %empty-directory(%t)
+// RUN: cd %t && %target-swift-frontend -interpret %S/../Inputs/empty.swift
+// RUN: not ls %t/*