Index: include/clang/AST/ASTImporter.h
===================================================================
--- include/clang/AST/ASTImporter.h
+++ include/clang/AST/ASTImporter.h
@@ -32,6 +32,7 @@
 namespace clang {
 
 class ASTContext;
+class Attr;
 class ASTImporterLookupTable;
 class CXXBaseSpecifier;
 class CXXCtorInitializer;
@@ -42,8 +43,8 @@
 class NamedDecl;
 class Stmt;
 class TagDecl;
+class TranslationUnitDecl;
 class TypeSourceInfo;
-class Attr;
 
   class ImportError : public llvm::ErrorInfo<ImportError> {
   public:
@@ -115,6 +116,10 @@
     /// context to the corresponding declarations in the "to" context.
     llvm::DenseMap<Decl *, Decl *> ImportedDecls;
 
+    /// Mapping from the already-imported declarations in the "to"
+    /// context to the corresponding declarations in the "from" context.
+    llvm::DenseMap<Decl *, Decl *> ImportedFromDecls;
+
     /// Mapping from the already-imported statements in the "from"
     /// context to the corresponding statements in the "to" context.
     llvm::DenseMap<Stmt *, Stmt *> ImportedStmts;
@@ -226,9 +231,13 @@
 
     /// Return the copy of the given declaration in the "to" context if
     /// it has already been imported from the "from" context.  Otherwise return
-    /// NULL.
+    /// nullptr.
     Decl *GetAlreadyImportedOrNull(const Decl *FromD) const;
 
+    /// Return the translation unit from where the declaration was
+    /// imported. If it does not exist nullptr is returned.
+    TranslationUnitDecl *GetFromTU(Decl *ToD);
+
     /// Import the given declaration context from the "from"
     /// AST context into the "to" AST context.
     ///
Index: lib/AST/ASTImporter.cpp
===================================================================
--- lib/AST/ASTImporter.cpp
+++ lib/AST/ASTImporter.cpp
@@ -437,6 +437,9 @@
 
     Error ImportTemplateInformation(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
+    template <typename T>
+    bool hasSameVisibilityContext(T *Found, T *From);
+
     bool IsStructuralMatch(Decl *From, Decl *To, bool Complain);
     bool IsStructuralMatch(RecordDecl *FromRecord, RecordDecl *ToRecord,
                            bool Complain = true);
@@ -2944,6 +2947,19 @@
   return FoundSpec;
 }
 
+template <typename T>
+bool ASTNodeImporter::hasSameVisibilityContext(T *Found, T *From) {
+  if (From->hasExternalFormalLinkage())
+    return Found->hasExternalFormalLinkage();
+  if (Importer.GetFromTU(Found) != From->getTranslationUnitDecl())
+    return false;
+  if (From->isInAnonymousNamespace())
+    return Found->isInAnonymousNamespace();
+  else
+    return !Found->isInAnonymousNamespace() &&
+           !Found->hasExternalFormalLinkage();
+}
+
 ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
 
   SmallVector<Decl *, 2> Redecls = getCanonicalForwardRedeclChain(D);
@@ -2997,33 +3013,30 @@
         continue;
 
       if (auto *FoundFunction = dyn_cast<FunctionDecl>(FoundDecl)) {
-        if (FoundFunction->hasExternalFormalLinkage() &&
-            D->hasExternalFormalLinkage()) {
-          if (IsStructuralMatch(D, FoundFunction)) {
-            const FunctionDecl *Definition = nullptr;
-            if (D->doesThisDeclarationHaveABody() &&
-                FoundFunction->hasBody(Definition)) {
-              return Importer.MapImported(
-                  D, const_cast<FunctionDecl *>(Definition));
-            }
-            FoundByLookup = FoundFunction;
-            break;
-          }
-
-          // FIXME: Check for overloading more carefully, e.g., by boosting
-          // Sema::IsOverload out to the AST library.
+        if (!hasSameVisibilityContext(FoundFunction, D))
+          continue;
+
+        if (IsStructuralMatch(D, FoundFunction)) {
+          const FunctionDecl *Definition = nullptr;
+          if (D->doesThisDeclarationHaveABody() &&
+              FoundFunction->hasBody(Definition))
+            return Importer.MapImported(D,
+                                        const_cast<FunctionDecl *>(Definition));
+          FoundByLookup = FoundFunction;
+          break;
+        }
+        // FIXME: Check for overloading more carefully, e.g., by boosting
+        // Sema::IsOverload out to the AST library.
 
-          // Function overloading is okay in C++.
-          if (Importer.getToContext().getLangOpts().CPlusPlus)
-            continue;
+        // Function overloading is okay in C++.
+        if (Importer.getToContext().getLangOpts().CPlusPlus)
+          continue;
 
-          // Complain about inconsistent function types.
-          Importer.ToDiag(Loc, diag::err_odr_function_type_inconsistent)
+        // Complain about inconsistent function types.
+        Importer.ToDiag(Loc, diag::err_odr_function_type_inconsistent)
             << Name << D->getType() << FoundFunction->getType();
-          Importer.ToDiag(FoundFunction->getLocation(),
-                          diag::note_odr_value_here)
+        Importer.ToDiag(FoundFunction->getLocation(), diag::note_odr_value_here)
             << FoundFunction->getType();
-        }
       }
 
       ConflictingDecls.push_back(FoundDecl);
@@ -3579,58 +3592,56 @@
         continue;
 
       if (auto *FoundVar = dyn_cast<VarDecl>(FoundDecl)) {
-        // We have found a variable that we may need to merge with. Check it.
-        if (FoundVar->hasExternalFormalLinkage() &&
-            D->hasExternalFormalLinkage()) {
-          if (Importer.IsStructurallyEquivalent(D->getType(),
-                                                FoundVar->getType())) {
-
-            // The VarDecl in the "From" context has a definition, but in the
-            // "To" context we already have a definition.
-            VarDecl *FoundDef = FoundVar->getDefinition();
-            if (D->isThisDeclarationADefinition() && FoundDef)
-              // FIXME Check for ODR error if the two definitions have
-              // different initializers?
-              return Importer.MapImported(D, FoundDef);
-
-            // The VarDecl in the "From" context has an initializer, but in the
-            // "To" context we already have an initializer.
-            const VarDecl *FoundDInit = nullptr;
-            if (D->getInit() && FoundVar->getAnyInitializer(FoundDInit))
-              // FIXME Diagnose ODR error if the two initializers are different?
-              return Importer.MapImported(D, const_cast<VarDecl*>(FoundDInit));
+        if (!hasSameVisibilityContext(FoundVar, D))
+          continue;
+        if (Importer.IsStructurallyEquivalent(D->getType(),
+                                              FoundVar->getType())) {
+
+          // The VarDecl in the "From" context has a definition, but in the
+          // "To" context we already have a definition.
+          VarDecl *FoundDef = FoundVar->getDefinition();
+          if (D->isThisDeclarationADefinition() && FoundDef)
+            // FIXME Check for ODR error if the two definitions have
+            // different initializers?
+            return Importer.MapImported(D, FoundDef);
+
+          // The VarDecl in the "From" context has an initializer, but in the
+          // "To" context we already have an initializer.
+          const VarDecl *FoundDInit = nullptr;
+          if (D->getInit() && FoundVar->getAnyInitializer(FoundDInit))
+            // FIXME Diagnose ODR error if the two initializers are different?
+            return Importer.MapImported(D, const_cast<VarDecl*>(FoundDInit));
+
+          FoundByLookup = FoundVar;
+          break;
+        }
+
+        const ArrayType *FoundArray
+          = Importer.getToContext().getAsArrayType(FoundVar->getType());
+        const ArrayType *TArray
+          = Importer.getToContext().getAsArrayType(D->getType());
+        if (FoundArray && TArray) {
+          if (isa<IncompleteArrayType>(FoundArray) &&
+              isa<ConstantArrayType>(TArray)) {
+            // Import the type.
+            if (auto TyOrErr = import(D->getType()))
+              FoundVar->setType(*TyOrErr);
+            else
+              return TyOrErr.takeError();
 
             FoundByLookup = FoundVar;
             break;
+          } else if (isa<IncompleteArrayType>(TArray) &&
+                     isa<ConstantArrayType>(FoundArray)) {
+            FoundByLookup = FoundVar;
+            break;
           }
-
-          const ArrayType *FoundArray
-            = Importer.getToContext().getAsArrayType(FoundVar->getType());
-          const ArrayType *TArray
-            = Importer.getToContext().getAsArrayType(D->getType());
-          if (FoundArray && TArray) {
-            if (isa<IncompleteArrayType>(FoundArray) &&
-                isa<ConstantArrayType>(TArray)) {
-              // Import the type.
-              if (auto TyOrErr = import(D->getType()))
-                FoundVar->setType(*TyOrErr);
-              else
-                return TyOrErr.takeError();
-
-              FoundByLookup = FoundVar;
-              break;
-            } else if (isa<IncompleteArrayType>(TArray) &&
-                       isa<ConstantArrayType>(FoundArray)) {
-              FoundByLookup = FoundVar;
-              break;
-            }
-          }
-
-          Importer.ToDiag(Loc, diag::err_odr_variable_type_inconsistent)
-            << Name << D->getType() << FoundVar->getType();
-          Importer.ToDiag(FoundVar->getLocation(), diag::note_odr_value_here)
-            << FoundVar->getType();
         }
+
+        Importer.ToDiag(Loc, diag::err_odr_variable_type_inconsistent)
+          << Name << D->getType() << FoundVar->getType();
+        Importer.ToDiag(FoundVar->getLocation(), diag::note_odr_value_here)
+          << FoundVar->getType();
       }
 
       ConflictingDecls.push_back(FoundDecl);
@@ -7761,6 +7772,13 @@
     return nullptr;
 }
 
+TranslationUnitDecl *ASTImporter::GetFromTU(Decl *ToD) {
+  auto FromDPos = ImportedFromDecls.find(ToD);
+  if (FromDPos == ImportedFromDecls.end())
+    return nullptr;
+  return FromDPos->second->getTranslationUnitDecl();
+}
+
 Expected<Decl *> ASTImporter::Import_New(Decl *FromD) {
   Decl *ToD = Import(FromD);
   if (!ToD && FromD)
@@ -8511,6 +8529,9 @@
   if (Pos != ImportedDecls.end())
     return Pos->second;
   ImportedDecls[From] = To;
+  // This mapping should be maintained only in this function. Therefore do not
+  // check for additional consistency.
+  ImportedFromDecls[To] = From;
   return To;
 }
 
Index: unittests/AST/ASTImporterTest.cpp
===================================================================
--- unittests/AST/ASTImporterTest.cpp
+++ unittests/AST/ASTImporterTest.cpp
@@ -10,6 +10,10 @@
 //
 //===----------------------------------------------------------------------===//
 
+// Define this to have ::testing::Combine available.
+// FIXME: Better solution for this?
+#define GTEST_HAS_COMBINE 1
+
 #include "clang/AST/ASTImporter.h"
 #include "MatchVerifier.h"
 #include "clang/AST/ASTContext.h"
@@ -58,23 +62,31 @@
 // Common base for the different families of ASTImporter tests that are
 // parameterized on the compiler options which may result a different AST. E.g.
 // -fms-compatibility or -fdelayed-template-parsing.
-struct ParameterizedTestsFixture : ::testing::TestWithParam<ArgVector> {
+class CompilerOptionSpecificTest : public ::testing::Test {
+protected:
+  // Return the extra arguments appended to runtime options at compilation.
+  virtual ArgVector getExtraArgs() const { return ArgVector(); }
 
   // Returns the argument vector used for a specific language option, this set
   // can be tweaked by the test parameters.
   ArgVector getArgVectorForLanguage(Language Lang) const {
     ArgVector Args = getBasicRunOptionsForLanguage(Lang);
-    ArgVector ExtraArgs = GetParam();
+    ArgVector ExtraArgs = getExtraArgs();
     for (const auto &Arg : ExtraArgs) {
       Args.push_back(Arg);
     }
     return Args;
   }
-
 };
 
+auto DefaultTestValuesForRunOptions = ::testing::Values(
+    ArgVector(), ArgVector{"-fdelayed-template-parsing"},
+    ArgVector{"-fms-compatibility"},
+    ArgVector{"-fdelayed-template-parsing", "-fms-compatibility"});
+
 // Base class for those tests which use the family of `testImport` functions.
-class TestImportBase : public ParameterizedTestsFixture {
+class TestImportBase : public CompilerOptionSpecificTest,
+                       public ::testing::WithParamInterface<ArgVector> {
 
   template <typename NodeType>
   NodeType importNode(ASTUnit *From, ASTUnit *To, ASTImporter &Importer,
@@ -159,6 +171,9 @@
         VerificationMatcher);
   }
 
+protected:
+  ArgVector getExtraArgs() const override { return GetParam(); }
+
 public:
 
   /// Test how AST node named "declToImport" located in the translation unit
@@ -284,7 +299,7 @@
 // This class provides generic methods to write tests which can check internal
 // attributes of AST nodes like getPreviousDecl(), isVirtual(), etc. Also,
 // this fixture makes it possible to import from several "From" contexts.
-class ASTImporterTestBase : public ParameterizedTestsFixture {
+class ASTImporterTestBase : public CompilerOptionSpecificTest {
 
   const char *const InputFileName = "input.cc";
   const char *const OutputFileName = "output.cc";
@@ -450,6 +465,10 @@
     return FromTU->import(*LookupTablePtr, ToAST.get(), From);
   }
 
+  template <class DeclT> DeclT *Import(DeclT *From, Language Lang) {
+    return cast_or_null<DeclT>(Import(cast<Decl>(From), Lang));
+  }
+
   QualType ImportType(QualType FromType, Decl *TUDecl, Language ToLang) {
     lazyInitToAST(ToLang, "", OutputFileName);
     TU *FromTU = findFromTU(TUDecl);
@@ -473,11 +492,18 @@
   }
 };
 
+class ASTImporterOptionSpecificTestBase
+    : public ASTImporterTestBase,
+      public ::testing::WithParamInterface<ArgVector> {
+protected:
+  ArgVector getExtraArgs() const override { return GetParam(); }
+};
+
 struct ImportExpr : TestImportBase {};
 struct ImportType : TestImportBase {};
 struct ImportDecl : TestImportBase {};
 
-struct CanonicalRedeclChain : ASTImporterTestBase {};
+struct CanonicalRedeclChain : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(CanonicalRedeclChain, ShouldBeConsequentWithMatchers) {
   Decl *FromTU = getTuDecl("void f();", Lang_CXX);
@@ -1000,7 +1026,7 @@
                  has(declStmt(hasSingleDecl(varDecl(hasName("d")))))))));
 }
 
-TEST_P(ASTImporterTestBase, ImportRecordTypeInFunc) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportRecordTypeInFunc) {
   Decl *FromTU = getTuDecl("int declToImport() { "
                            "  struct data_t {int a;int b;};"
                            "  struct data_t d;"
@@ -1015,7 +1041,7 @@
   EXPECT_FALSE(ToType.isNull());
 }
 
-TEST_P(ASTImporterTestBase, ImportRecordDeclInFuncParams) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportRecordDeclInFuncParams) {
   // This construct is not supported by ASTImporter.
   Decl *FromTU = getTuDecl(
       "int declToImport(struct data_t{int a;int b;} ***d){ return 0; }",
@@ -1027,7 +1053,7 @@
   EXPECT_EQ(To, nullptr);
 }
 
-TEST_P(ASTImporterTestBase, ImportRecordDeclInFuncFromMacro) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportRecordDeclInFuncFromMacro) {
   Decl *FromTU = getTuDecl(
       "#define NONAME_SIZEOF(type) sizeof(struct{type *dummy;}) \n"
       "int declToImport(){ return NONAME_SIZEOF(int); }",
@@ -1042,7 +1068,8 @@
                        hasDescendant(unaryExprOrTypeTraitExpr()))));
 }
 
-TEST_P(ASTImporterTestBase, ImportRecordDeclInFuncParamsFromMacro) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportRecordDeclInFuncParamsFromMacro) {
   // This construct is not supported by ASTImporter.
   Decl *FromTU = getTuDecl(
       "#define PAIR_STRUCT(type) struct data_t{type a;type b;} \n"
@@ -1194,7 +1221,8 @@
           has(fieldDecl(hasType(dependentSizedArrayType())))))));
 }
 
-TEST_P(ASTImporterTestBase, ImportOfTemplatedDeclOfClassTemplateDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportOfTemplatedDeclOfClassTemplateDecl) {
   Decl *FromTU = getTuDecl("template<class X> struct S{};", Lang_CXX);
   auto From =
       FirstDeclMatcher<ClassTemplateDecl>().match(FromTU, classTemplateDecl());
@@ -1207,7 +1235,8 @@
   EXPECT_EQ(ToTemplated1, ToTemplated);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfTemplatedDeclOfFunctionTemplateDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportOfTemplatedDeclOfFunctionTemplateDecl) {
   Decl *FromTU = getTuDecl("template<class X> void f(){}", Lang_CXX);
   auto From = FirstDeclMatcher<FunctionTemplateDecl>().match(
       FromTU, functionTemplateDecl());
@@ -1220,7 +1249,7 @@
   EXPECT_EQ(ToTemplated1, ToTemplated);
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ImportOfTemplatedDeclShouldImportTheClassTemplateDecl) {
   Decl *FromTU = getTuDecl("template<class X> struct S{};", Lang_CXX);
   auto FromFT =
@@ -1236,7 +1265,7 @@
   EXPECT_TRUE(ToFT);
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ImportOfTemplatedDeclShouldImportTheFunctionTemplateDecl) {
   Decl *FromTU = getTuDecl("template<class X> void f(){}", Lang_CXX);
   auto FromFT = FirstDeclMatcher<FunctionTemplateDecl>().match(
@@ -1252,7 +1281,7 @@
   EXPECT_TRUE(ToFT);
 }
 
-TEST_P(ASTImporterTestBase, ImportCorrectTemplatedDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportCorrectTemplatedDecl) {
   auto Code =
         R"(
         namespace x {
@@ -1283,7 +1312,8 @@
   ASSERT_EQ(ToTemplated1, ToTemplated);
 }
 
-TEST_P(ASTImporterTestBase, ImportFunctionWithBackReferringParameter) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportFunctionWithBackReferringParameter) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
@@ -1310,7 +1340,7 @@
   EXPECT_TRUE(Verifier.match(To, Matcher));
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        TUshouldNotContainTemplatedDeclOfFunctionTemplates) {
   Decl *From, *To;
   std::tie(From, To) =
@@ -1336,7 +1366,8 @@
   EXPECT_TRUE(Check(To));
 }
 
-TEST_P(ASTImporterTestBase, TUshouldNotContainTemplatedDeclOfClassTemplates) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       TUshouldNotContainTemplatedDeclOfClassTemplates) {
   Decl *From, *To;
   std::tie(From, To) =
       getImportedDecl("template <typename T> struct declToImport { T t; };"
@@ -1361,7 +1392,8 @@
   EXPECT_TRUE(Check(To));
 }
 
-TEST_P(ASTImporterTestBase, TUshouldNotContainTemplatedDeclOfTypeAlias) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       TUshouldNotContainTemplatedDeclOfTypeAlias) {
   Decl *From, *To;
   std::tie(From, To) =
       getImportedDecl(
@@ -1388,9 +1420,8 @@
   EXPECT_TRUE(Check(To));
 }
 
-TEST_P(
-    ASTImporterTestBase,
-    TUshouldNotContainClassTemplateSpecializationOfImplicitInstantiation) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       TUshouldNotContainClassTemplateSpecializationOfImplicitInstantiation) {
 
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
@@ -1431,7 +1462,7 @@
   return Index == Order.size();
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        TUshouldContainClassTemplateSpecializationOfExplicitInstantiation) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
@@ -1458,7 +1489,8 @@
   EXPECT_TRUE(MatchVerifier<Decl>{}.match(To, Pattern));
 }
 
-TEST_P(ASTImporterTestBase, CXXRecordDeclFieldsShouldBeInCorrectOrder) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       CXXRecordDeclFieldsShouldBeInCorrectOrder) {
   Decl *From, *To;
   std::tie(From, To) =
       getImportedDecl(
@@ -1470,7 +1502,7 @@
   EXPECT_TRUE(Verifier.match(To, cxxRecordDecl(hasFieldOrder({"a", "b"}))));
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        DISABLED_CXXRecordDeclFieldOrderShouldNotDependOnImportOrder) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
@@ -1492,7 +1524,7 @@
       Verifier.match(To, cxxRecordDecl(hasFieldOrder({"a", "b", "c"}))));
 }
 
-TEST_P(ASTImporterTestBase, ShouldImportImplicitCXXRecordDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase, ShouldImportImplicitCXXRecordDecl) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
@@ -1508,7 +1540,8 @@
   EXPECT_TRUE(Verifier.match(To, Matcher));
 }
 
-TEST_P(ASTImporterTestBase, ShouldImportImplicitCXXRecordDeclOfClassTemplate) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ShouldImportImplicitCXXRecordDeclOfClassTemplate) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
@@ -1525,9 +1558,8 @@
   EXPECT_TRUE(Verifier.match(To, Matcher));
 }
 
-TEST_P(
-    ASTImporterTestBase,
-    ShouldImportImplicitCXXRecordDeclOfClassTemplateSpecializationDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ShouldImportImplicitCXXRecordDeclOfClassTemplateSpecializationDecl) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
@@ -1547,7 +1579,7 @@
       MatchVerifier<Decl>{}.match(To->getTranslationUnitDecl(), Pattern));
 }
 
-TEST_P(ASTImporterTestBase, IDNSOrdinary) {
+TEST_P(ASTImporterOptionSpecificTestBase, IDNSOrdinary) {
   Decl *From, *To;
   std::tie(From, To) =
       getImportedDecl("void declToImport() {}", Lang_CXX, "", Lang_CXX);
@@ -1559,7 +1591,7 @@
   EXPECT_EQ(From->getIdentifierNamespace(), To->getIdentifierNamespace());
 }
 
-TEST_P(ASTImporterTestBase, IDNSOfNonmemberOperator) {
+TEST_P(ASTImporterOptionSpecificTestBase, IDNSOfNonmemberOperator) {
   Decl *FromTU = getTuDecl(
       R"(
       struct X {};
@@ -1571,7 +1603,7 @@
   EXPECT_EQ(From->getIdentifierNamespace(), To->getIdentifierNamespace());
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ShouldImportMembersOfClassTemplateSpecializationDecl) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
@@ -1591,7 +1623,8 @@
       MatchVerifier<Decl>{}.match(To->getTranslationUnitDecl(), Pattern));
 }
 
-TEST_P(ASTImporterTestBase, ImportDefinitionOfClassTemplateAfterFwdDecl) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportDefinitionOfClassTemplateAfterFwdDecl) {
   {
     Decl *FromTU = getTuDecl(
         R"(
@@ -1624,7 +1657,7 @@
   }
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ImportDefinitionOfClassTemplateIfThereIsAnExistingFwdDeclAndDefinition) {
   Decl *ToTU = getToTuDecl(
       R"(
@@ -1664,7 +1697,7 @@
                     .match(ToTU, classTemplateDecl()));
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ImportDefinitionOfClassIfThereIsAnExistingFwdDeclAndDefinition) {
   Decl *ToTU = getToTuDecl(
       R"(
@@ -1707,7 +1740,7 @@
   CompareSourceLocs(FullSourceLoc{ Range1.getEnd(), SM1 },
                     FullSourceLoc{ Range2.getEnd(), SM2 });
 }
-TEST_P(ASTImporterTestBase, ImportSourceLocs) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportSourceLocs) {
   Decl *FromTU = getTuDecl(
       R"(
       #define MFOO(arg) arg = arg + 1
@@ -1737,7 +1770,7 @@
                       FromSM);
 }
 
-TEST_P(ASTImporterTestBase, ImportNestedMacro) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportNestedMacro) {
   Decl *FromTU = getTuDecl(
       R"(
       #define FUNC_INT void declToImport
@@ -1755,9 +1788,8 @@
 }
 
 TEST_P(
-    ASTImporterTestBase,
-    ImportDefinitionOfClassTemplateSpecIfThereIsAnExistingFwdDeclAndDefinition)
-{
+    ASTImporterOptionSpecificTestBase,
+    ImportDefinitionOfClassTemplateSpecIfThereIsAnExistingFwdDeclAndDefinition) {
   Decl *ToTU = getToTuDecl(
       R"(
       template <typename T>
@@ -1799,7 +1831,7 @@
                     .match(ToTU, classTemplateSpecializationDecl()));
 }
 
-TEST_P(ASTImporterTestBase, ObjectsWithUnnamedStructType) {
+TEST_P(ASTImporterOptionSpecificTestBase, ObjectsWithUnnamedStructType) {
   Decl *FromTU = getTuDecl(
       R"(
       struct { int a; int b; } object0 = { 2, 3 };
@@ -1823,7 +1855,7 @@
   EXPECT_NE(To0->getCanonicalDecl(), To1->getCanonicalDecl());
 }
 
-TEST_P(ASTImporterTestBase, AnonymousRecords) {
+TEST_P(ASTImporterOptionSpecificTestBase, AnonymousRecords) {
   auto *Code =
       R"(
       struct X {
@@ -1849,7 +1881,7 @@
             DeclCounter<RecordDecl>().match(ToTU, recordDecl(hasName("X"))));
 }
 
-TEST_P(ASTImporterTestBase, AnonymousRecordsReversed) {
+TEST_P(ASTImporterOptionSpecificTestBase, AnonymousRecordsReversed) {
   Decl *FromTU0 = getTuDecl(
       R"(
       struct X {
@@ -1882,7 +1914,7 @@
             DeclCounter<RecordDecl>().match(ToTU, recordDecl(hasName("X"))));
 }
 
-TEST_P(ASTImporterTestBase, ImportDoesUpdateUsedFlag) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportDoesUpdateUsedFlag) {
   auto Pattern = varDecl(hasName("x"));
   VarDecl *Imported1;
   {
@@ -1908,7 +1940,7 @@
   EXPECT_TRUE(Imported2->isUsed(false));
 }
 
-TEST_P(ASTImporterTestBase, ImportDoesUpdateUsedFlag2) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportDoesUpdateUsedFlag2) {
   auto Pattern = varDecl(hasName("x"));
   VarDecl *ExistingD;
   {
@@ -1926,7 +1958,7 @@
   EXPECT_TRUE(ExistingD->isUsed(false));
 }
 
-TEST_P(ASTImporterTestBase, ImportDoesUpdateUsedFlag3) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportDoesUpdateUsedFlag3) {
   auto Pattern = varDecl(hasName("a"));
   VarDecl *ExistingD;
   {
@@ -1957,7 +1989,7 @@
   EXPECT_TRUE(ExistingD->isUsed(false));
 }
 
-TEST_P(ASTImporterTestBase, ReimportWithUsedFlag) {
+TEST_P(ASTImporterOptionSpecificTestBase, ReimportWithUsedFlag) {
   auto Pattern = varDecl(hasName("x"));
 
   Decl *FromTU = getTuDecl("int x;", Lang_CXX, "input0.cc");
@@ -1974,7 +2006,7 @@
   EXPECT_TRUE(Imported2->isUsed(false));
 }
 
-struct ImportFunctions : ASTImporterTestBase {};
+struct ImportFunctions : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportFunctions,
        DefinitionShouldBeImportedAsDefintionWhenThereIsAPrototype) {
@@ -2232,6 +2264,266 @@
             }).match(ToTU, functionDecl()));
 }
 
+//FIXME Move these tests to a separate test file.
+namespace TypeAndValueParameterizedTests {
+
+// Type parameters for type-parameterized test fixtures.
+struct GetFunPattern {
+  using DeclTy = FunctionDecl;
+  BindableMatcher<Decl> operator()() { return functionDecl(hasName("f")); }
+};
+struct GetVarPattern {
+  using DeclTy = VarDecl;
+  BindableMatcher<Decl> operator()() { return varDecl(hasName("v")); }
+};
+
+// Values for the value-parameterized test fixtures.
+// FunctionDecl:
+auto *ExternF = "void f();";
+auto *StaticF = "static void f();";
+auto *AnonF = "namespace { void f(); }";
+// VarDecl:
+auto *ExternV = "extern int v;";
+auto *StaticV = "static int v;";
+auto *AnonV = "namespace { extern int v; }";
+
+// First value in tuple: Compile options.
+// Second value in tuple: Source code to be used in the test.
+using ImportVisibilityChainParams =
+    ::testing::WithParamInterface<std::tuple<ArgVector, const char *>>;
+// Fixture to test the redecl chain of Decls with the same visibility.  Gtest
+// makes it possible to have either value-parameterized or type-parameterized
+// fixtures.  However, we cannot have both value- and type-parameterized test
+// fixtures.  This is a value-parameterized test fixture in the gtest sense. We
+// intend to mimic gtest's type-parameters via the PatternFactory template
+// parameter.  We manually instantiate the different tests with the each types.
+template <typename PatternFactory>
+class ImportVisibilityChain
+    : public ASTImporterTestBase, public ImportVisibilityChainParams {
+protected:
+  using DeclTy = typename PatternFactory::DeclTy;
+  ArgVector getExtraArgs() const override { return std::get<0>(GetParam()); }
+  std::string getCode() const { return std::get<1>(GetParam()); }
+  BindableMatcher<Decl> getPattern() const { return PatternFactory()(); }
+
+  // Type-parameterized test.
+  void TypedTest_ImportChain() {
+    std::string Code = getCode() + getCode();
+    auto Pattern = getPattern();
+
+    TranslationUnitDecl *FromTu = getTuDecl(Code, Lang_CXX, "input0.cc");
+
+    auto *FromF0 = FirstDeclMatcher<DeclTy>().match(FromTu, Pattern);
+    auto *FromF1 = LastDeclMatcher<DeclTy>().match(FromTu, Pattern);
+
+    auto *ToF0 = Import(FromF0, Lang_CXX);
+    auto *ToF1 = Import(FromF1, Lang_CXX);
+
+    EXPECT_TRUE(ToF0);
+    ASSERT_TRUE(ToF1);
+    EXPECT_NE(ToF0, ToF1);
+    EXPECT_EQ(ToF1->getPreviousDecl(), ToF0);
+  }
+};
+
+// Manual instantiation of the fixture with each type.
+using ImportFunctionsVisibilityChain = ImportVisibilityChain<GetFunPattern>;
+using ImportVariablesVisibilityChain = ImportVisibilityChain<GetVarPattern>;
+// Value-parameterized test for the first type.
+TEST_P(ImportFunctionsVisibilityChain, ImportChain) {
+  TypedTest_ImportChain();
+}
+// Value-parameterized test for the second type.
+TEST_P(ImportVariablesVisibilityChain, ImportChain) {
+  TypedTest_ImportChain();
+}
+
+// Automatic instantiation of the value-parameterized tests.
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFunctionsVisibilityChain,
+                        ::testing::Combine(
+                           DefaultTestValuesForRunOptions,
+                           ::testing::Values(ExternF, StaticF, AnonF)), );
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportVariablesVisibilityChain,
+    ::testing::Combine(
+        DefaultTestValuesForRunOptions,
+        // There is no point to instantiate with StaticV, because in C++ we can
+        // forward declare a variable only with the 'extern' keyword.
+        // Consequently, each fwd declared variable has external linkage.  This
+        // is different in the C language where any declaration without an
+        // initializer is a tentative definition, subsequent definitions may be
+        // provided but they must have the same linkage.  See also the test
+        // ImportVariableChainInC which test for this special C Lang case.
+        ::testing::Values(ExternV, AnonV)), );
+
+// First value in tuple: Compile options.
+// Second value in tuple: Tuple with informations for the test.
+// Code for first import (or initial code), code to import, whether the `f`
+// functions are expected to be linked in a declaration chain.
+// One value of this tuple is combined with every value of compile options.
+// The test can have a single tuple as parameter only.
+using ImportVisibilityParams = ::testing::WithParamInterface<
+    std::tuple<ArgVector, std::tuple<const char *, const char *, bool>>>;
+
+template <typename PatternFactory>
+class ImportVisibility
+    : public ASTImporterTestBase,
+      public ImportVisibilityParams {
+protected:
+  using DeclTy = typename PatternFactory::DeclTy;
+  ArgVector getExtraArgs() const override { return std::get<0>(GetParam()); }
+  std::string getCode0() const { return std::get<0>(std::get<1>(GetParam())); }
+  std::string getCode1() const { return std::get<1>(std::get<1>(GetParam())); }
+  bool shouldBeLinked() const { return std::get<2>(std::get<1>(GetParam())); }
+  BindableMatcher<Decl> getPattern() const { return PatternFactory()(); }
+
+  void TypedTest_ImportAfter() {
+    TranslationUnitDecl *ToTu = getToTuDecl(getCode0(), Lang_CXX);
+    TranslationUnitDecl *FromTu = getTuDecl(getCode1(), Lang_CXX, "input1.cc");
+
+    auto *ToF0 = FirstDeclMatcher<DeclTy>().match(ToTu, getPattern());
+    auto *FromF1 = FirstDeclMatcher<DeclTy>().match(FromTu, getPattern());
+
+    auto *ToF1 = Import(FromF1, Lang_CXX);
+
+    ASSERT_TRUE(ToF0);
+    ASSERT_TRUE(ToF1);
+    EXPECT_NE(ToF0, ToF1);
+
+    if (shouldBeLinked())
+      EXPECT_EQ(ToF1->getPreviousDecl(), ToF0);
+    else
+      EXPECT_FALSE(ToF1->getPreviousDecl());
+  }
+
+  void TypedTest_ImportAfterImport() {
+    TranslationUnitDecl *FromTu0 = getTuDecl(getCode0(), Lang_CXX, "input0.cc");
+    TranslationUnitDecl *FromTu1 = getTuDecl(getCode1(), Lang_CXX, "input1.cc");
+    auto *FromF0 =
+        FirstDeclMatcher<DeclTy>().match(FromTu0, getPattern());
+    auto *FromF1 =
+        FirstDeclMatcher<DeclTy>().match(FromTu1, getPattern());
+    auto *ToF0 = Import(FromF0, Lang_CXX);
+    auto *ToF1 = Import(FromF1, Lang_CXX);
+    ASSERT_TRUE(ToF0);
+    ASSERT_TRUE(ToF1);
+    EXPECT_NE(ToF0, ToF1);
+    if (shouldBeLinked())
+      EXPECT_EQ(ToF1->getPreviousDecl(), ToF0);
+    else
+      EXPECT_FALSE(ToF1->getPreviousDecl());
+  }
+};
+using ImportFunctionsVisibility = ImportVisibility<GetFunPattern>;
+using ImportVariablesVisibility = ImportVisibility<GetVarPattern>;
+
+// FunctionDecl.
+TEST_P(ImportFunctionsVisibility, ImportAfter) {
+  TypedTest_ImportAfter();
+}
+TEST_P(ImportFunctionsVisibility, ImportAfterImport) {
+  TypedTest_ImportAfterImport();
+}
+// VarDecl.
+TEST_P(ImportVariablesVisibility, ImportAfter) {
+  TypedTest_ImportAfter();
+}
+TEST_P(ImportVariablesVisibility, ImportAfterImport) {
+  TypedTest_ImportAfterImport();
+}
+
+bool ExpectLink = true;
+bool ExpectNotLink = false;
+
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportFunctionsVisibility,
+    ::testing::Combine(
+        DefaultTestValuesForRunOptions,
+        ::testing::Values(std::make_tuple(ExternF, ExternF, ExpectLink),
+                          std::make_tuple(ExternF, StaticF, ExpectNotLink),
+                          std::make_tuple(ExternF, AnonF, ExpectNotLink),
+                          std::make_tuple(StaticF, ExternF, ExpectNotLink),
+                          std::make_tuple(StaticF, StaticF, ExpectNotLink),
+                          std::make_tuple(StaticF, AnonF, ExpectNotLink),
+                          std::make_tuple(AnonF, ExternF, ExpectNotLink),
+                          std::make_tuple(AnonF, StaticF, ExpectNotLink),
+                          std::make_tuple(AnonF, AnonF, ExpectNotLink))), );
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportVariablesVisibility,
+    ::testing::Combine(
+        DefaultTestValuesForRunOptions,
+        ::testing::Values(std::make_tuple(ExternV, ExternV, ExpectLink),
+                          std::make_tuple(ExternV, StaticV, ExpectNotLink),
+                          std::make_tuple(ExternV, AnonV, ExpectNotLink),
+                          std::make_tuple(StaticV, ExternV, ExpectNotLink),
+                          std::make_tuple(StaticV, StaticV, ExpectNotLink),
+                          std::make_tuple(StaticV, AnonV, ExpectNotLink),
+                          std::make_tuple(AnonV, ExternV, ExpectNotLink),
+                          std::make_tuple(AnonV, StaticV, ExpectNotLink),
+                          std::make_tuple(AnonV, AnonV, ExpectNotLink))), );
+
+} // namespace TypeAndValueParameterizedTests
+
+TEST_P(ASTImporterOptionSpecificTestBase, ImportVariableChainInC) {
+    std::string Code = "static int v; static int v = 0;";
+    auto Pattern = varDecl(hasName("v"));
+
+    TranslationUnitDecl *FromTu = getTuDecl(Code, Lang_C, "input0.c");
+
+    auto *From0 = FirstDeclMatcher<VarDecl>().match(FromTu, Pattern);
+    auto *From1 = LastDeclMatcher<VarDecl>().match(FromTu, Pattern);
+
+    auto *To0 = Import(From0, Lang_C);
+    auto *To1 = Import(From1, Lang_C);
+
+    EXPECT_TRUE(To0);
+    ASSERT_TRUE(To1);
+    EXPECT_NE(To0, To1);
+    EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportFunctions, ImportFromDifferentScopedAnonNamespace) {
+  TranslationUnitDecl *FromTu = getTuDecl(
+      "namespace NS0 { namespace { void f(); } }"
+      "namespace NS1 { namespace { void f(); } }",
+      Lang_CXX, "input0.cc");
+  auto Pattern = functionDecl(hasName("f"));
+
+  auto *FromF0 = FirstDeclMatcher<FunctionDecl>().match(FromTu, Pattern);
+  auto *FromF1 = LastDeclMatcher<FunctionDecl>().match(FromTu, Pattern);
+
+  auto *ToF0 = Import(FromF0, Lang_CXX);
+  auto *ToF1 = Import(FromF1, Lang_CXX);
+
+  EXPECT_TRUE(ToF0);
+  ASSERT_TRUE(ToF1);
+  EXPECT_NE(ToF0, ToF1);
+  EXPECT_FALSE(ToF1->getPreviousDecl());
+}
+
+TEST_P(ImportFunctions, ImportFunctionFromUnnamedNamespace) {
+  {
+    Decl *FromTU = getTuDecl("namespace { void f() {} } void g0() { f(); }",
+                             Lang_CXX, "input0.cc");
+    auto *FromD = FirstDeclMatcher<FunctionDecl>().match(
+        FromTU, functionDecl(hasName("g0")));
+
+    Import(FromD, Lang_CXX);
+  }
+  {
+    Decl *FromTU =
+        getTuDecl("namespace { void f() { int a; } } void g1() { f(); }",
+                  Lang_CXX, "input1.cc");
+    auto *FromD = FirstDeclMatcher<FunctionDecl>().match(
+        FromTU, functionDecl(hasName("g1")));
+    Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, functionDecl(hasName("f"))),
+            2u);
+}
+
 struct ImportFriendFunctions : ImportFunctions {};
 
 TEST_P(ImportFriendFunctions, ImportFriendFunctionRedeclChainProto) {
@@ -2700,7 +2992,7 @@
                  compoundStmt(has(callExpr(has(unresolvedMemberExpr())))))))));
 }
 
-class ImportImplicitMethods : public ASTImporterTestBase {
+class ImportImplicitMethods : public ASTImporterOptionSpecificTestBase {
 public:
   static constexpr auto DefaultCode = R"(
       struct A { int x; };
@@ -2812,7 +3104,7 @@
   testNoImportOf(cxxMethodDecl(hasName("f")), Code);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfEquivalentRecord) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfEquivalentRecord) {
   Decl *ToR1;
   {
     Decl *FromTU = getTuDecl(
@@ -2836,7 +3128,7 @@
   EXPECT_EQ(ToR1, ToR2);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfNonEquivalentRecord) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfNonEquivalentRecord) {
   Decl *ToR1;
   {
     Decl *FromTU = getTuDecl(
@@ -2856,7 +3148,7 @@
   EXPECT_NE(ToR1, ToR2);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfEquivalentField) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfEquivalentField) {
   Decl *ToF1;
   {
     Decl *FromTU = getTuDecl(
@@ -2876,7 +3168,7 @@
   EXPECT_EQ(ToF1, ToF2);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfNonEquivalentField) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfNonEquivalentField) {
   Decl *ToF1;
   {
     Decl *FromTU = getTuDecl(
@@ -2896,7 +3188,7 @@
   EXPECT_NE(ToF1, ToF2);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfEquivalentMethod) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfEquivalentMethod) {
   Decl *ToM1;
   {
     Decl *FromTU = getTuDecl(
@@ -2916,7 +3208,7 @@
   EXPECT_EQ(ToM1, ToM2);
 }
 
-TEST_P(ASTImporterTestBase, ImportOfNonEquivalentMethod) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportOfNonEquivalentMethod) {
   Decl *ToM1;
   {
     Decl *FromTU = getTuDecl(
@@ -2938,7 +3230,8 @@
   EXPECT_NE(ToM1, ToM2);
 }
 
-TEST_P(ASTImporterTestBase, ImportUnnamedStructsWithRecursingField) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportUnnamedStructsWithRecursingField) {
   Decl *FromTU = getTuDecl(
       R"(
       struct A {
@@ -2970,7 +3263,7 @@
       R1, recordDecl(has(fieldDecl(hasName("next"))))));
 }
 
-TEST_P(ASTImporterTestBase, ImportUnnamedFieldsInCorrectOrder) {
+TEST_P(ASTImporterOptionSpecificTestBase, ImportUnnamedFieldsInCorrectOrder) {
   Decl *FromTU = getTuDecl(
       R"(
       void f(int X, int Y, bool Z) {
@@ -3005,7 +3298,8 @@
   EXPECT_EQ(FromIndex, 3u);
 }
 
-TEST_P(ASTImporterTestBase, MergeFieldDeclsOfClassTemplateSpecialization) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       MergeFieldDeclsOfClassTemplateSpecialization) {
   std::string ClassTemplate =
       R"(
       template <typename T>
@@ -3050,7 +3344,8 @@
   EXPECT_TRUE(ToField->getInClassInitializer());
 }
 
-TEST_P(ASTImporterTestBase, MergeFunctionOfClassTemplateSpecialization) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       MergeFunctionOfClassTemplateSpecialization) {
   std::string ClassTemplate =
       R"(
       template <typename T>
@@ -3091,7 +3386,7 @@
   EXPECT_TRUE(ToFun->hasBody());
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ODRViolationOfClassTemplateSpecializationsShouldBeReported) {
   std::string ClassTemplate =
       R"(
@@ -3138,7 +3433,8 @@
                     ToTU, classTemplateSpecializationDecl()));
 }
 
-TEST_P(ASTImporterTestBase, MergeCtorOfClassTemplateSpecialization) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       MergeCtorOfClassTemplateSpecialization) {
   std::string ClassTemplate =
       R"(
       template <typename T>
@@ -3179,7 +3475,7 @@
   EXPECT_TRUE(ToCtor->hasBody());
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
        ClassTemplatePartialSpecializationsShouldNotBeDuplicated) {
   auto Code =
       R"(
@@ -3206,7 +3502,8 @@
                     ToTU, classTemplatePartialSpecializationDecl()));
 }
 
-TEST_P(ASTImporterTestBase, ClassTemplateSpecializationsShouldNotBeDuplicated) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ClassTemplateSpecializationsShouldNotBeDuplicated) {
   auto Code =
       R"(
     // primary template
@@ -3230,7 +3527,8 @@
                    ToTU, classTemplateSpecializationDecl()));
 }
 
-TEST_P(ASTImporterTestBase, ClassTemplateFullAndPartialSpecsShouldNotBeMixed) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ClassTemplateFullAndPartialSpecsShouldNotBeMixed) {
   std::string PrimaryTemplate =
       R"(
     template<class T1, class T2, int I>
@@ -3262,7 +3560,8 @@
                               unless(classTemplatePartialSpecializationDecl()))));
 }
 
-TEST_P(ASTImporterTestBase, InitListExprValueKindShouldBeImported) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       InitListExprValueKindShouldBeImported) {
   Decl *TU = getTuDecl(
       R"(
       const int &init();
@@ -3281,7 +3580,7 @@
   EXPECT_TRUE(ToInitExpr->isGLValue());
 }
 
-struct ImportVariables : ASTImporterTestBase {};
+struct ImportVariables : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportVariables, ImportOfOneDeclBringsInTheWholeChain) {
   Decl *FromTU = getTuDecl(
@@ -3369,7 +3668,7 @@
   EXPECT_TRUE(ImportedD->getDefinition());
 }
 
-struct ImportClasses : ASTImporterTestBase {};
+struct ImportClasses : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportClasses,
        PrototypeShouldBeImportedAsAPrototypeWhenThereIsNoDefinition) {
@@ -3577,7 +3876,7 @@
   EXPECT_EQ(ToDef->getPreviousDecl(), ToProto);
 }
 
-struct ImportClassTemplates : ASTImporterTestBase {};
+struct ImportClassTemplates : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportClassTemplates,
        PrototypeShouldBeImportedAsAPrototypeWhenThereIsNoDefinition) {
@@ -3741,7 +4040,7 @@
             ToProto->getTemplatedDecl());
 }
 
-struct ImportFriendClasses : ASTImporterTestBase {};
+struct ImportFriendClasses : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportFriendClasses, ImportOfFriendRecordDoesNotMergeDefinition) {
   Decl *FromTU = getTuDecl(
@@ -3981,7 +4280,7 @@
   EXPECT_EQ(ImportedFwd, ImportedDef->getPreviousDecl());
 }
 
-TEST_P(ASTImporterTestBase, FriendFunInClassTemplate) {
+TEST_P(ASTImporterOptionSpecificTestBase, FriendFunInClassTemplate) {
   auto *Code = R"(
   template <class T>
   struct X {
@@ -3999,7 +4298,7 @@
   EXPECT_EQ(ImportedFoo, ToFoo);
 }
 
-struct DeclContextTest : ASTImporterTestBase {};
+struct DeclContextTest : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(DeclContextTest, removeDeclOfClassTemplateSpecialization) {
   Decl *TU = getTuDecl(
@@ -4062,7 +4361,8 @@
   EXPECT_FALSE(DC->containsDecl(A0));
 }
 
-struct ImportFunctionTemplateSpecializations : ASTImporterTestBase {};
+struct ImportFunctionTemplateSpecializations
+    : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportFunctionTemplateSpecializations,
        TUshouldNotContainFunctionTemplateImplicitInstantiation) {
@@ -4377,7 +4677,7 @@
   EXPECT_EQ(To1->getPreviousDecl(), To0);
 }
 
-TEST_P(ASTImporterTestBase,
+TEST_P(ASTImporterOptionSpecificTestBase,
     ImportShouldNotReportFalseODRErrorWhenRecordIsBeingDefined) {
   {
     Decl *FromTU = getTuDecl(
@@ -4416,7 +4716,8 @@
   }
 }
 
-TEST_P(ASTImporterTestBase, ImportingTypedefShouldImportTheCompleteType) {
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportingTypedefShouldImportTheCompleteType) {
   // We already have an incomplete underlying type in the "To" context.
   auto Code =
       R"(
@@ -4448,7 +4749,7 @@
   EXPECT_FALSE(ImportedD->getUnderlyingType()->isIncompleteType());
 }
 
-struct ASTImporterLookupTableTest : ASTImporterTestBase {};
+struct ASTImporterLookupTableTest : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ASTImporterLookupTableTest, OneDecl) {
   auto *ToTU = getToTuDecl("int a;", Lang_CXX);
@@ -4865,12 +5166,6 @@
     ParameterizedTests, CanonicalRedeclChain,
     ::testing::Values(ArgVector()),);
 
-auto DefaultTestValuesForRunOptions = ::testing::Values(
-    ArgVector(),
-    ArgVector{"-fdelayed-template-parsing"},
-    ArgVector{"-fms-compatibility"},
-    ArgVector{"-fdelayed-template-parsing", "-fms-compatibility"});
-
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterLookupTableTest,
                         DefaultTestValuesForRunOptions, );
 
@@ -4883,7 +5178,7 @@
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportDecl,
                         DefaultTestValuesForRunOptions, );
 
-INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterTestBase,
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterOptionSpecificTestBase,
                         DefaultTestValuesForRunOptions, );
 
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFunctions,