Clang importer: feed a Clang prepprocessor through to canInferDefaultArgument.

Omitting needless words while importing the full name function
involves inference of default arguments, so we can get here while
building Swift name lookup tables. It takes a lot of machinery to
trigger this problem; tests forthcoming.

There *must* be a better way to ensure this never happens, but it
requires a bit more refactoring in the Clang importer.

Author: DougGregor

lib/ClangImporter/ClangImporter.cpp

@@ -2492,6 +2492,7 @@ auto ClangImporter::Implementation::importFullName(
     // Objective-C methods.
     if (auto method = dyn_cast<clang::ObjCMethodDecl>(D)) {
       (void)omitNeedlessWordsInFunctionName(
+        clangSema.getPreprocessor(),
         baseName,
         argumentNames,
         params,

lib/ClangImporter/ImportType.cpp

@@ -1705,6 +1705,7 @@ OmissionTypeName ClangImporter::Implementation::getClangTypeNameForOmission(
 
 /// Attempt to omit needless words from the given function name.
 bool ClangImporter::Implementation::omitNeedlessWordsInFunctionName(
+       clang::Preprocessor &pp,
        StringRef &baseName,
        SmallVectorImpl<StringRef> &argumentNames,
        ArrayRef<const clang::ParmVarDecl *> params,
@@ -1739,6 +1740,7 @@ bool ClangImporter::Implementation::omitNeedlessWordsInFunctionName(
     // parameter.
     bool hasDefaultArg
       = canInferDefaultArgument(
+          pp,
           param->getType(),
           getParamOptionality(param,
                               !nonNullArgs.empty() && nonNullArgs[i],
@@ -1792,8 +1794,9 @@ clang::QualType ClangImporter::Implementation::getClangDeclContextType(
 }
 
 bool ClangImporter::Implementation::canInferDefaultArgument(
-       clang::QualType type, OptionalTypeKind clangOptionality,
-       Identifier baseName, unsigned numParams, bool isLastParameter) {
+       clang::Preprocessor &pp, clang::QualType type,
+       OptionalTypeKind clangOptionality, Identifier baseName,
+       unsigned numParams, bool isLastParameter) {
   // Don't introduce a default argument for setters with only a single
   // parameter.
   if (numParams == 1 && camel_case::getFirstWord(baseName.str()) == "set")
@@ -1819,8 +1822,7 @@ bool ClangImporter::Implementation::canInferDefaultArgument(
 
   // Option sets default to "[]" if they have "Options" in their name.
   if (const clang::EnumType *enumTy = type->getAs<clang::EnumType>())
-    if (classifyEnum(getClangPreprocessor(), enumTy->getDecl())
-          == EnumKind::Options) {
+    if (classifyEnum(pp, enumTy->getDecl()) == EnumKind::Options) {
       auto enumName = enumTy->getDecl()->getName();
       for (auto word : reversed(camel_case::getWords(enumName))) {
         if (camel_case::sameWordIgnoreFirstCase(word, "options"))
@@ -2135,7 +2137,8 @@ Type ClangImporter::Implementation::importMethodType(
     if (InferDefaultArguments &&
         (kind == SpecialMethodKind::Regular ||
          kind == SpecialMethodKind::Constructor) &&
-        canInferDefaultArgument(param->getType(), optionalityOfParam,
+        canInferDefaultArgument(getClangPreprocessor(),
+                                param->getType(), optionalityOfParam,
                                 methodName.getBaseName(), numEffectiveParams,
                                 isLastParameter)) {
       defaultArg = DefaultArgumentKind::Normal;

lib/ClangImporter/ImporterImpl.h

@@ -743,6 +743,7 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
 
   /// Omit needless words in a function name.
   bool omitNeedlessWordsInFunctionName(
+         clang::Preprocessor &pp,
          StringRef &baseName,
          SmallVectorImpl<StringRef> &argumentNames,
          ArrayRef<const clang::ParmVarDecl *> params,
@@ -1125,7 +1126,8 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
 
   /// Determine whether we can infer a default argument for a parameter with
   /// the given \c type and (Clang) optionality.
-  bool canInferDefaultArgument(clang::QualType type,
+  bool canInferDefaultArgument(clang::Preprocessor &pp,
+                               clang::QualType type,
                                OptionalTypeKind clangOptionality,
                                Identifier baseName,
                                unsigned numParams,