[Frontend] Validate ImplicitImportModuleNames early

Check whether the user has provided a valid
identifier when parsing the options. Also make
ImplicitImportModuleNames a private member of
FrontendOptions to prevent mutation after being
parsed.

Author: hamishknight

include/swift/Frontend/FrontendOptions.h

@@ -33,6 +33,9 @@ namespace swift {
 class FrontendOptions {
   friend class ArgsToFrontendOptionsConverter;
 
+  /// A list of arbitrary modules to import and make implicitly visible.
+  std::vector<std::string> ImplicitImportModuleNames;
+
 public:
   FrontendInputsAndOutputs InputsAndOutputs;
 
@@ -44,9 +47,6 @@ class FrontendOptions {
 
   bool isOutputFileDirectory() const;
 
-  /// A list of arbitrary modules to import and make implicitly visible.
-  std::vector<std::string> ImplicitImportModuleNames;
-
   /// An Objective-C header to import and make implicitly visible.
   std::string ImplicitObjCHeaderPath;
 
@@ -322,6 +322,12 @@ class FrontendOptions {
   const PrimarySpecificPaths &
       getPrimarySpecificPathsForPrimary(StringRef) const;
 
+  /// Retrieves the list of arbitrary modules to import and make implicitly
+  /// visible.
+  ArrayRef<std::string> getImplicitImportModuleNames() const {
+    return ImplicitImportModuleNames;
+  }
+
 private:
   static bool canActionEmitDependencies(ActionType);
   static bool canActionEmitReferenceDependencies(ActionType);

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -564,7 +564,13 @@ void ArgsToFrontendOptionsConverter::computeImportObjCHeaderOptions() {
 void ArgsToFrontendOptionsConverter::computeImplicitImportModuleNames() {
   using namespace options;
   for (const Arg *A : Args.filtered(OPT_import_module)) {
-    Opts.ImplicitImportModuleNames.push_back(A->getValue());
+    auto *moduleStr = A->getValue();
+    if (!Lexer::isIdentifier(moduleStr)) {
+      Diags.diagnose(SourceLoc(), diag::error_bad_module_name, moduleStr,
+                     /*suggestModuleNameFlag*/ false);
+      continue;
+    }
+    Opts.ImplicitImportModuleNames.push_back(moduleStr);
   }
 }
 void ArgsToFrontendOptionsConverter::computeLLVMArgs() {

lib/Frontend/Frontend.cpp

@@ -882,7 +882,7 @@ void CompilerInstance::getImplicitlyImportedModules(
     SmallVectorImpl<ModuleDecl *> &importModules) {
   FrontendStatsTracer tracer(getStatsReporter(), "get-implicitly-imported-modules");
   for (auto &ImplicitImportModuleName :
-       Invocation.getFrontendOptions().ImplicitImportModuleNames) {
+       Invocation.getFrontendOptions().getImplicitImportModuleNames()) {
     if (Lexer::isIdentifier(ImplicitImportModuleName)) {
       auto moduleID = Context->getIdentifier(ImplicitImportModuleName);
       ModuleDecl *importModule =

tools/SourceKit/lib/SwiftLang/CodeCompletionOrganizer.cpp

@@ -337,7 +337,7 @@ ImportDepth::ImportDepth(ASTContext &context,
   // specially by applying import depth 0.
   llvm::StringSet<> auxImports;
   for (StringRef moduleName :
-       invocation.getFrontendOptions().ImplicitImportModuleNames)
+       invocation.getFrontendOptions().getImplicitImportModuleNames())
     auxImports.insert(moduleName);
 
   // Private imports from this module.