FrontendInputs data structure redo.

- Outlaw duplicate input files, fix driver, fix tests, and add test.
- Reflect that no buffer is present without a (possibly pseudo) named file.
- Reflect fact that every input has a (possible pseudo) name.
- Break up CompilerInstance::setup.

Don't bail on dups.

Author: David Ungar

include/swift/AST/DiagnosticsFrontend.def

@@ -157,6 +157,9 @@ ERROR(error_primary_file_not_found,none,
 ERROR(error_cannot_have_input_files_with_file_list,none,
 "cannot have input files with file list", ())
 
+ERROR(error_duplicate_input_file,none,
+"duplicate input file '%0'", (StringRef))
+
 ERROR(repl_must_be_initialized,none,
       "variables currently must have an initial value when entered at the "
       "top level of the REPL", ())

include/swift/Frontend/Frontend.h

@@ -242,20 +242,6 @@ class CompilerInvocation {
     return FrontendOpts.ModuleName;
   }
 
-  void addInputFilename(StringRef Filename) {
-    FrontendOpts.Inputs.addInputFilename(Filename);
-  }
-
-  /// Does not take ownership of \p Buf.
-  void addInputBuffer(llvm::MemoryBuffer *Buf) {
-    FrontendOpts.Inputs.addInputBuffer(Buf);
-  }
-
-  void setPrimaryInput(SelectedInput pi) {
-    FrontendOpts.Inputs.setPrimaryInput(pi);
-  }
-
-  void clearInputs() { FrontendOpts.Inputs.clearInputs(); }
 
   StringRef getOutputFilename() const {
     return FrontendOpts.getSingleOutputFilename();
@@ -307,7 +293,7 @@ class CompilerInvocation {
   /// Return value includes the buffer so caller can keep it alive.
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
   setUpInputForSILTool(StringRef inputFilename, StringRef moduleNameArg,
-                       bool alwaysSetModuleToMain,
+                       bool alwaysSetModuleToMain, bool bePrimary,
                        serialization::ExtendedValidationInfo &extendedInfo);
   bool hasSerializedAST() {
     return FrontendOpts.InputKind == InputFileKind::IFK_Swift_Library;
@@ -359,8 +345,6 @@ class CompilerInstance {
   void createSILModule();
   void setPrimarySourceFile(SourceFile *SF);
 
-  bool setUpForFileAt(unsigned i);
-
 public:
   SourceManager &getSourceMgr() { return SourceMgr; }
 
@@ -436,6 +420,23 @@ class CompilerInstance {
   /// \brief Returns true if there was an error during setup.
   bool setup(const CompilerInvocation &Invocation);
 
+private:
+  void setUpLLVMArguments();
+  void setUpDiagnosticOptions();
+  bool setUpModuleLoaders();
+  Optional<unsigned> setupCodeCompletionBuffer();
+  bool setupInputs(Optional<unsigned> codeCompletionBufferID);
+  bool isInMainMode() {
+    return Invocation.getInputKind() == InputFileKind::IFK_Swift;
+  }
+  bool isInSILMode() {
+    return Invocation.getInputKind() == InputFileKind::IFK_SIL;
+  }
+  bool setupForInput(const InputFile &input);
+  void setupForBuffer(llvm::MemoryBuffer *buffer, bool isPrimary);
+  bool setUpForFile(StringRef file, bool isPrimary);
+
+public:
   /// Parses and type-checks all input files.
   void performSema();
 
@@ -445,6 +446,13 @@ class CompilerInstance {
   ///
   void performParseOnly(bool EvaluateConditionals = false);
 
+private:
+  SourceFile *
+  createSourceFileForMainModule(SourceFileKind FileKind,
+                                SourceFile::ImplicitModuleImportKind ImportKind,
+                                Optional<unsigned> BufferID);
+
+public:
   /// Frees up the ASTContext and SILModule objects that this instance is
   /// holding on.
   void freeContextAndSIL();
@@ -469,7 +477,7 @@ class CompilerInstance {
   };
 
 private:
-  void createREPLFile(const ImplicitImports &implicitImports) const;
+  void createREPLFile(const ImplicitImports &implicitImports);
   std::unique_ptr<DelayedParsingCallbacks>
   computeDelayedParsingCallback(bool isPrimary);