martong updated this revision to Diff 149107.
martong added a comment.

- Add a missing "else"


Repository:
  rC Clang

https://reviews.llvm.org/D47532

Files:
  include/clang/AST/ASTImporter.h
  lib/AST/ASTImporter.cpp
  lib/AST/DeclBase.cpp
  test/ASTMerge/class/test.cpp
  unittests/AST/ASTImporterTest.cpp

Index: unittests/AST/ASTImporterTest.cpp
===================================================================
--- unittests/AST/ASTImporterTest.cpp
+++ unittests/AST/ASTImporterTest.cpp
@@ -20,7 +20,7 @@
 
 #include "DeclMatcher.h"
 #include "Language.h"
-#include "gtest/gtest.h"
+#include "gmock/gmock.h"
 #include "llvm/ADT/StringMap.h"
 
 namespace clang {
@@ -425,6 +425,48 @@
   }
 }
 
+struct CanonicalRedeclChain : ASTImporterTestBase {};
+
+TEST_P(CanonicalRedeclChain, ShouldBeConsequentWithMatchers) {
+  Decl *FromTU = getTuDecl("void f();", Lang_CXX);
+  auto Pattern = functionDecl(hasName("f"));
+  auto D0 = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto Redecls = getCanonicalForwardRedeclChain(D0);
+  ASSERT_EQ(Redecls.size(), 1u);
+  EXPECT_EQ(D0, Redecls[0]);
+}
+
+TEST_P(CanonicalRedeclChain, ShouldBeConsequentWithMatchers2) {
+  Decl *FromTU = getTuDecl("void f(); void f(); void f();", Lang_CXX);
+  auto Pattern = functionDecl(hasName("f"));
+  auto D0 = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  auto D2 = LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  FunctionDecl *D1 = D2->getPreviousDecl();
+
+  auto Redecls = getCanonicalForwardRedeclChain(D0);
+  ASSERT_EQ(Redecls.size(), 3u);
+  EXPECT_EQ(D0, Redecls[0]);
+  EXPECT_EQ(D1, Redecls[1]);
+  EXPECT_EQ(D2, Redecls[2]);
+}
+
+TEST_P(CanonicalRedeclChain, ShouldBeSameForAllDeclInTheChain) {
+  Decl *FromTU = getTuDecl("void f(); void f(); void f();", Lang_CXX);
+  auto Pattern = functionDecl(hasName("f"));
+  auto D0 = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  auto D2 = LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  FunctionDecl *D1 = D2->getPreviousDecl();
+
+  auto RedeclsD0 = getCanonicalForwardRedeclChain(D0);
+  auto RedeclsD1 = getCanonicalForwardRedeclChain(D1);
+  auto RedeclsD2 = getCanonicalForwardRedeclChain(D2);
+
+  EXPECT_THAT(RedeclsD0, ::testing::ContainerEq(RedeclsD1));
+  EXPECT_THAT(RedeclsD1, ::testing::ContainerEq(RedeclsD2));
+}
+
+
 TEST(ImportExpr, ImportStringLiteral) {
   MatchVerifier<Decl> Verifier;
   testImport("void declToImport() { \"foo\"; }",
@@ -1607,41 +1649,9 @@
                     .match(ToTU, classTemplateSpecializationDecl()));
 }
 
-INSTANTIATE_TEST_CASE_P(
-    ParameterizedTests, ASTImporterTestBase,
-    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
-
 struct ImportFunctions : ASTImporterTestBase {};
 
 TEST_P(ImportFunctions,
-       PrototypeShouldBeImportedAsAPrototypeWhenThereIsNoDefinition) {
-  Decl *FromTU = getTuDecl("void f();", Lang_CXX);
-  auto Pattern = functionDecl(hasName("f"));
-  FunctionDecl *FromD =
-      FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-
-  Decl *ImportedD = Import(FromD, Lang_CXX);
-  Decl *ToTU = ImportedD->getTranslationUnitDecl();
-
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_TRUE(!cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
-}
-
-TEST_P(ImportFunctions,
-       PrototypeShouldBeImportedAsDefintionWhenThereIsADefinition) {
-  Decl *FromTU = getTuDecl("void f(); void f() {}", Lang_CXX);
-  auto Pattern = functionDecl(hasName("f"));
-  FunctionDecl *FromD = // Prototype
-      FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-
-  Decl *ImportedD = Import(FromD, Lang_CXX);
-  Decl *ToTU = ImportedD->getTranslationUnitDecl();
-
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
-}
-
-TEST_P(ImportFunctions,
        DefinitionShouldBeImportedAsDefintionWhenThereIsAPrototype) {
   Decl *FromTU = getTuDecl("void f(); void f() {}", Lang_CXX);
   auto Pattern = functionDecl(hasName("f"));
@@ -1651,7 +1661,7 @@
   Decl *ImportedD = Import(FromD, Lang_CXX);
   Decl *ToTU = ImportedD->getTranslationUnitDecl();
 
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
   EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
 }
 
@@ -1668,80 +1678,116 @@
   EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
 }
 
-TEST_P(ImportFunctions, DISABLED_ImportPrototypeOfRecursiveFunction) {
+TEST_P(ImportFunctions, ImportPrototypeOfRecursiveFunction) {
   Decl *FromTU = getTuDecl("void f(); void f() { f(); }", Lang_CXX);
   auto Pattern = functionDecl(hasName("f"));
-  FunctionDecl *PrototypeFD =
-      FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  auto From =
+      FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern); // Proto
 
-  Decl *ImportedD = Import(PrototypeFD, Lang_CXX);
+  Decl *ImportedD = Import(From, Lang_CXX);
   Decl *ToTU = ImportedD->getTranslationUnitDecl();
 
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
 }
 
 TEST_P(ImportFunctions, ImportDefinitionOfRecursiveFunction) {
   Decl *FromTU = getTuDecl("void f(); void f() { f(); }", Lang_CXX);
   auto Pattern = functionDecl(hasName("f"));
-  FunctionDecl *DefinitionFD =
-      LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+  auto From =
+      LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern); // Def
 
-  Decl *ImportedD = Import(DefinitionFD, Lang_CXX);
+  Decl *ImportedD = Import(From, Lang_CXX);
   Decl *ToTU = ImportedD->getTranslationUnitDecl();
 
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To1);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
 }
 
 TEST_P(ImportFunctions, ImportPrototypes) {
   auto Pattern = functionDecl(hasName("f"));
 
   Decl *ImportedD;
   {
     Decl *FromTU = getTuDecl("void f();", Lang_CXX, "input0.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
 
     ImportedD = Import(FromD, Lang_CXX);
   }
-  Decl *ImportedD1;
   {
     Decl *FromTU = getTuDecl("void f();", Lang_CXX, "input1.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-    ImportedD1 = Import(FromD, Lang_CXX);
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    Import(FromD, Lang_CXX);
   }
 
-  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportFunctions, ImportDefinitions) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl("void f(){}", Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+  {
+    Decl *FromTU = getTuDecl("void f(){};", Lang_CXX, "input1.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
   EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_EQ(ImportedD, ImportedD1);
-  EXPECT_TRUE(!cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(To0->doesThisDeclarationHaveABody());
 }
 
 TEST_P(ImportFunctions, ImportDefinitionThenPrototype) {
   auto Pattern = functionDecl(hasName("f"));
 
   Decl *ImportedD;
   {
     Decl *FromTU = getTuDecl("void f(){}", Lang_CXX, "input0.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
     ImportedD = Import(FromD, Lang_CXX);
   }
-  Decl *ImportedD1;
   {
     Decl *FromTU = getTuDecl("void f();", Lang_CXX, "input1.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-    ImportedD1 = Import(FromD, Lang_CXX);
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    Import(FromD, Lang_CXX);
   }
 
   Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
-  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
-  EXPECT_EQ(ImportedD, ImportedD1);
-  EXPECT_TRUE(cast<FunctionDecl>(ImportedD)->doesThisDeclarationHaveABody());
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
 }
 
 TEST_P(ImportFunctions, ImportPrototypeThenDefinition) {
@@ -1771,31 +1817,33 @@
   EXPECT_EQ(DefinitionD->getPreviousDecl(), ProtoD);
 }
 
-TEST_P(ImportFunctions, DISABLED_ImportPrototypeThenProtoAndDefinition) {
+TEST_P(ImportFunctions,
+       ImportPrototypeThenProtoAndDefinition) {
   auto Pattern = functionDecl(hasName("f"));
 
   {
     Decl *FromTU = getTuDecl("void f();", Lang_CXX, "input0.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
-
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
     Import(FromD, Lang_CXX);
   }
   {
     Decl *FromTU = getTuDecl("void f(); void f(){}", Lang_CXX, "input1.cc");
-    FunctionDecl *FromD =
-        FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
     Import(FromD, Lang_CXX);
   }
 
   Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
-  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
-  FunctionDecl *ProtoD = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 3u);
+  FunctionDecl* ProtoD = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
   EXPECT_TRUE(!ProtoD->doesThisDeclarationHaveABody());
-  FunctionDecl *DefinitionD =
-      LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+
+  FunctionDecl* DefinitionD = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
   EXPECT_TRUE(DefinitionD->doesThisDeclarationHaveABody());
-  EXPECT_EQ(DefinitionD->getPreviousDecl(), ProtoD);
+
+  EXPECT_TRUE(DefinitionD->getPreviousDecl());
+  EXPECT_TRUE(!DefinitionD->getPreviousDecl()->doesThisDeclarationHaveABody());
+  EXPECT_EQ(DefinitionD->getPreviousDecl()->getPreviousDecl(), ProtoD);
 }
 
 TEST_P(ImportFunctions, OverriddenMethodsShouldBeImported) {
@@ -1835,9 +1883,185 @@
   EXPECT_TRUE(To->isVirtual());
 }
 
-INSTANTIATE_TEST_CASE_P(
-    ParameterizedTests, ImportFunctions,
-    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
+TEST_P(ImportFunctions,
+       ImportDefinitionIfThereIsAnExistingDefinitionAndFwdDecl) {
+  Decl *ToTU = getToTuDecl(
+      R"(
+      void f() {}
+      void f();
+      )",
+      Lang_CXX);
+  ASSERT_EQ(1u,
+            DeclCounterWithPredicate<FunctionDecl>([](const FunctionDecl *FD) {
+              return FD->doesThisDeclarationHaveABody();
+            }).match(ToTU, functionDecl()));
+
+  Decl *FromTU = getTuDecl("void f() {}", Lang_CXX, "input0.cc");
+  auto *FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+
+  Import(FromD, Lang_CXX);
+
+  EXPECT_EQ(1u,
+            DeclCounterWithPredicate<FunctionDecl>([](const FunctionDecl *FD) {
+              return FD->doesThisDeclarationHaveABody();
+            }).match(ToTU, functionDecl()));
+}
+
+struct ImportFriendFunctions : ImportFunctions {};
+
+TEST_P(ImportFriendFunctions, ImportFriendFunctionRedeclChainProto) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl("struct X { friend void f(); };"
+                           "void f();",
+                           Lang_CXX,
+                           "input0.cc");
+  auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(!ImportedD->doesThisDeclarationHaveABody());
+  auto ToFD = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(!ToFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ToFD->getPreviousDecl(), ImportedD);
+}
+
+TEST_P(ImportFriendFunctions,
+       ImportFriendFunctionRedeclChainProto_OutOfClassProtoFirst) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl("void f();"
+                           "struct X { friend void f(); };",
+                           Lang_CXX, "input0.cc");
+  auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(!ImportedD->doesThisDeclarationHaveABody());
+  auto ToFD = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(!ToFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ToFD->getPreviousDecl(), ImportedD);
+}
+
+TEST_P(ImportFriendFunctions, ImportFriendFunctionRedeclChainDef) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl("struct X { friend void f(){} };"
+                           "void f();",
+                           Lang_CXX,
+                           "input0.cc");
+  auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(ImportedD->doesThisDeclarationHaveABody());
+  auto ToFD = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(!ToFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ToFD->getPreviousDecl(), ImportedD);
+}
+
+TEST_P(ImportFriendFunctions,
+       ImportFriendFunctionRedeclChainDef_OutOfClassDef) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl("struct X { friend void f(); };"
+                           "void f(){}",
+                           Lang_CXX, "input0.cc");
+  auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(!ImportedD->doesThisDeclarationHaveABody());
+  auto ToFD = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ToFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ToFD->getPreviousDecl(), ImportedD);
+}
+
+TEST_P(ImportFriendFunctions,
+    DISABLED_ImportFriendFunctionRedeclChainDefWithClass) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl(
+      R"(
+        class X;
+        void f(X *x){}
+        class X{
+        friend void f(X *x);
+        };
+      )",
+      Lang_CXX, "input0.cc");
+  auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(ImportedD->doesThisDeclarationHaveABody());
+  auto *InClassFD = cast<FunctionDecl>(FirstDeclMatcher<FriendDecl>()
+                                              .match(ToTU, friendDecl())
+                                              ->getFriendDecl());
+  EXPECT_TRUE(!InClassFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(InClassFD->getPreviousDecl(), ImportedD);
+  // The parameters must refer the same type
+  EXPECT_EQ((*InClassFD->param_begin())->getOriginalType(),
+            (*ImportedD->param_begin())->getOriginalType());
+}
+
+TEST_P(ImportFriendFunctions,
+       DISABLED_ImportFriendFunctionRedeclChainDefWithClass_ImportTheProto) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  Decl *FromTU = getTuDecl(
+      R"(
+        class X;
+        void f(X *x){}
+        class X{
+        friend void f(X *x);
+        };
+      )",
+      Lang_CXX, "input0.cc");
+  auto FromD = LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+  auto *ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(!ImportedD->doesThisDeclarationHaveABody());
+  auto *OutOfClassFD = FirstDeclMatcher<FunctionDecl>().match(
+      ToTU, functionDecl(unless(hasParent(friendDecl()))));
+
+  EXPECT_TRUE(OutOfClassFD->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ImportedD->getPreviousDecl(), OutOfClassFD);
+  // The parameters must refer the same type
+  EXPECT_EQ((*OutOfClassFD->param_begin())->getOriginalType(),
+            (*ImportedD->param_begin())->getOriginalType());
+}
+
+TEST_P(ImportFriendFunctions, ImportFriendFunctionFromMultipleTU) {
+  auto Pattern = functionDecl(hasName("f"));
+
+  FunctionDecl *ImportedD;
+  {
+    Decl *FromTU =
+        getTuDecl("struct X { friend void f(){} };", Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  }
+  FunctionDecl *ImportedD1;
+  {
+    Decl *FromTU = getTuDecl("void f();", Lang_CXX, "input1.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD1 = cast<FunctionDecl>(Import(FromD, Lang_CXX));
+  }
+
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  ASSERT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  EXPECT_TRUE(ImportedD->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!ImportedD1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(ImportedD1->getPreviousDecl(), ImportedD);
+}
 
 AST_MATCHER_P(TagDecl, hasTypedefForAnonDecl, Matcher<TypedefNameDecl>,
               InnerMatcher) {
@@ -1969,9 +2193,341 @@
   EXPECT_FALSE(NS->containsDecl(Spec));
 }
 
+struct ImportFunctionTemplateSpecializations : ASTImporterTestBase {};
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       TUshouldNotContainFunctionTemplateImplicitInstantiation) {
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      template<class T>
+      int f() { return 0; }
+      void foo() { f<int>(); }
+      )",
+      Lang_CXX, "input0.cc");
+
+  //Check that the function template instantiation is NOT the child of the TU
+  auto Pattern = translationUnitDecl(
+      unless(has(functionDecl(hasName("f"), isTemplateInstantiation()))));
+  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromTU, Pattern));
+
+  auto *Foo = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("foo")));
+  ASSERT_TRUE(Import(Foo, Lang_CXX));
+
+  auto ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToTU, Pattern));
+}
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       TUshouldNotContainFunctionTemplateExplicitInstantiation) {
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      template<class T>
+      int f() { return 0; }
+      template int f<int>();
+      )",
+      Lang_CXX, "input0.cc");
+
+  //Check that the function template instantiation is NOT the child of the TU
+  auto Instantiation = functionDecl(hasName("f"), isTemplateInstantiation());
+  auto Pattern = translationUnitDecl(unless(has(Instantiation)));
+  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromTU, Pattern));
+
+  ASSERT_TRUE(Import(FirstDeclMatcher<Decl>().match(FromTU, Instantiation), Lang_CXX));
+
+  auto ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToTU, Pattern));
+}
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       TUshouldContainFunctionTemplateSpecialization) {
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      template<class T>
+      int f() { return 0; }
+      template <> int f<int>() { return 4; }
+      )",
+      Lang_CXX, "input0.cc");
+
+  //Check that the function template specialization is the child of the TU
+  auto Specialization = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Pattern = translationUnitDecl(has(Specialization));
+  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromTU, Pattern));
+
+  ASSERT_TRUE(Import(FirstDeclMatcher<Decl>().match(FromTU, Specialization), Lang_CXX));
+
+  auto ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToTU, Pattern));
+}
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       FunctionTemplateSpecializationRedeclChain) {
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      template<class T>
+      int f() { return 0; }
+      template <> int f<int>() { return 4; }
+      )",
+      Lang_CXX, "input0.cc");
+
+  auto Spec = functionDecl(hasName("f"), isExplicitTemplateSpecialization(),
+                           hasParent(translationUnitDecl()));
+  auto *FromSpecD = FirstDeclMatcher<Decl>().match(FromTU, Spec);
+  {
+    auto *TU = FromTU;
+    auto *SpecD = FromSpecD;
+    auto *TemplateD = FirstDeclMatcher<FunctionTemplateDecl>().match(
+        TU, functionTemplateDecl());
+    auto *FirstSpecD = *(TemplateD->spec_begin());
+    ASSERT_EQ(SpecD, FirstSpecD);
+    ASSERT_TRUE(SpecD->getPreviousDecl());
+    ASSERT_FALSE(cast<FunctionDecl>(SpecD->getPreviousDecl())
+                     ->doesThisDeclarationHaveABody());
+  }
+
+  ASSERT_TRUE(Import(FromSpecD, Lang_CXX));
+
+  {
+    auto *TU = ToAST->getASTContext().getTranslationUnitDecl();
+    auto *SpecD = FirstDeclMatcher<Decl>().match(TU, Spec);
+    auto *TemplateD = FirstDeclMatcher<FunctionTemplateDecl>().match(
+        TU, functionTemplateDecl());
+    auto *FirstSpecD = *(TemplateD->spec_begin());
+    EXPECT_EQ(SpecD, FirstSpecD);
+    ASSERT_TRUE(SpecD->getPreviousDecl());
+    EXPECT_FALSE(cast<FunctionDecl>(SpecD->getPreviousDecl())
+                     ->doesThisDeclarationHaveABody());
+  }
+}
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       MatchNumberOfFunctionTemplateSpecializations) {
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      template <typename T> constexpr int f() { return 0; }
+      template <> constexpr int f<int>() { return 4; }
+      void foo() {
+        static_assert(f<char>() == 0, "");
+        static_assert(f<int>() == 4, "");
+      }
+      )",
+      Lang_CXX11, "input0.cc");
+  auto *FromD = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("foo")));
+
+  Import(FromD, Lang_CXX11);
+  auto ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  EXPECT_EQ(
+      DeclCounter<FunctionDecl>().match(FromTU, functionDecl(hasName("f"))),
+      DeclCounter<FunctionDecl>().match(ToTU, functionDecl(hasName("f"))));
+}
+
+TEST_P(ImportFunctionTemplateSpecializations,
+       ImportPrototypes) {
+  auto Pattern = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Code =
+      R"(
+      // Proto of the primary template.
+      template <class T>
+      void f();
+      // Proto of the specialization.
+      template <>
+      void f<int>();
+      )";
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input0.cc");
+    auto FromD = LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input1.cc");
+    auto FromD = LastDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(ImportedD != To1);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!To1->doesThisDeclarationHaveABody());
+  // Check that they are part of the same redecl chain.
+  EXPECT_EQ(To1->getCanonicalDecl(), To0->getCanonicalDecl());
+}
+
+TEST_P(ImportFunctionTemplateSpecializations, ImportDefinitions) {
+  auto Pattern = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Code =
+      R"(
+      // Proto of the primary template.
+      template <class T>
+      void f();
+      // Specialization and definition.
+      template <>
+      void f<int>() {}
+      )";
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input1.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 1u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(To0->doesThisDeclarationHaveABody());
+
+  auto *TemplateD = FirstDeclMatcher<FunctionTemplateDecl>().match(
+      ToTU, functionTemplateDecl());
+  auto *FirstSpecD = *(TemplateD->spec_begin());
+  EXPECT_EQ(FirstSpecD->getCanonicalDecl(), To0->getCanonicalDecl());
+}
+
+TEST_P(ImportFunctionTemplateSpecializations, PrototypeThenPrototype) {
+  auto Pattern = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Code =
+      R"(
+      // Proto of the primary template.
+      template <class T>
+      void f();
+      // Specialization proto.
+      template <>
+      void f<int>();
+      // Specialization proto.
+      template <>
+      void f<int>();
+      )";
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(ImportedD != To1);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportFunctionTemplateSpecializations, PrototypeThenDefinition) {
+  auto Pattern = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Code =
+      R"(
+      // Proto of the primary template.
+      template <class T>
+      void f();
+      // Specialization proto.
+      template <>
+      void f<int>();
+      // Specialization definition.
+      template <>
+      void f<int>() {}
+      )";
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(ImportedD != To1);
+  EXPECT_TRUE(!To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportFunctionTemplateSpecializations, DefinitionThenPrototype) {
+  auto Pattern = functionDecl(hasName("f"), isExplicitTemplateSpecialization());
+  auto Code =
+      R"(
+      // Proto of the primary template.
+      template <class T>
+      void f();
+      // Specialization definition.
+      template <>
+      void f<int>() {}
+      // Specialization proto.
+      template <>
+      void f<int>();
+      )";
+
+  Decl *ImportedD;
+  {
+    Decl *FromTU = getTuDecl(Code, Lang_CXX, "input0.cc");
+    auto FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, Pattern);
+    ImportedD = Import(FromD, Lang_CXX);
+  }
+
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<FunctionDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<FunctionDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == To0);
+  EXPECT_TRUE(ImportedD != To1);
+  EXPECT_TRUE(To0->doesThisDeclarationHaveABody());
+  EXPECT_TRUE(!To1->doesThisDeclarationHaveABody());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
 INSTANTIATE_TEST_CASE_P(
     ParameterizedTests, DeclContextTest,
     ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
 
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ASTImporterTestBase,
+    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
+
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportFriendFunctions,
+    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
+
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportFunctions,
+    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
+
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, ImportFunctionTemplateSpecializations,
+    ::testing::Values(ArgVector(), ArgVector{"-fdelayed-template-parsing"}),);
+
+INSTANTIATE_TEST_CASE_P(
+    ParameterizedTests, CanonicalRedeclChain,
+    ::testing::Values(ArgVector()),);
+
 } // end namespace ast_matchers
 } // end namespace clang
Index: test/ASTMerge/class/test.cpp
===================================================================
--- test/ASTMerge/class/test.cpp
+++ test/ASTMerge/class/test.cpp
@@ -13,12 +13,12 @@
 // CHECK: class1.cpp:19:3: note: enumerator 'b' with value 1 here
 // CHECK: class2.cpp:12:3: note: enumerator 'a' with value 0 here
 
-// CHECK: class1.cpp:36:8: warning: type 'F2' has incompatible definitions in different translation units
-// CHECK: class1.cpp:39:3: note: friend declared here
-// CHECK: class2.cpp:30:8: note: no corresponding friend here
-
 // CHECK: class1.cpp:43:8: warning: type 'F3' has incompatible definitions in different translation units
 // CHECK: class1.cpp:46:3: note: friend declared here
 // CHECK: class2.cpp:36:8: note: no corresponding friend here
 
+// CHECK: class1.cpp:36:8: warning: type 'F2' has incompatible definitions in different translation units
+// CHECK: class1.cpp:39:3: note: friend declared here
+// CHECK: class2.cpp:30:8: note: no corresponding friend here
+
 // CHECK: 4 warnings generated.
Index: lib/AST/DeclBase.cpp
===================================================================
--- lib/AST/DeclBase.cpp
+++ lib/AST/DeclBase.cpp
@@ -1343,6 +1343,8 @@
 }
 
 bool DeclContext::containsDecl(Decl *D) const {
+  if (hasExternalLexicalStorage())
+    LoadLexicalDeclsFromExternalStorage();
   return (D->getLexicalDeclContext() == this &&
           (D->NextInContextAndBits.getPointer() || D == LastDecl));
 }
Index: lib/AST/ASTImporter.cpp
===================================================================
--- lib/AST/ASTImporter.cpp
+++ lib/AST/ASTImporter.cpp
@@ -71,6 +71,25 @@
 
 namespace clang {
 
+  template <class T>
+  llvm::SmallVector<Decl*, 2>
+  getCanonicalForwardRedeclChain(Redeclarable<T>* D) {
+    llvm::SmallVector<Decl*, 2> Redecls;
+    for (auto R : D->getFirstDecl()->redecls()) {
+      if (R != D->getFirstDecl())
+        Redecls.push_back(R);
+    }
+    Redecls.push_back(D->getFirstDecl());
+    std::reverse(Redecls.begin(), Redecls.end());
+    return Redecls;
+  }
+
+  llvm::SmallVector<Decl*, 2> getCanonicalForwardRedeclChain(Decl* D) {
+    // Currently only FunctionDecl is supported
+    auto FD = cast<FunctionDecl>(D);
+    return getCanonicalForwardRedeclChain<FunctionDecl>(FD);
+  }
+
   class ASTNodeImporter : public TypeVisitor<ASTNodeImporter, QualType>,
                           public DeclVisitor<ASTNodeImporter, Decl *>,
                           public StmtVisitor<ASTNodeImporter, Stmt *> {
@@ -408,6 +427,8 @@
 
     // Importing overrides.
     void ImportOverrides(CXXMethodDecl *ToMethod, CXXMethodDecl *FromMethod);
+
+    FunctionDecl *FindFunctionTemplateSpecialization(FunctionDecl *FromFD);
   };
 
 template <typename InContainerTy>
@@ -2312,7 +2333,37 @@
   llvm_unreachable("All cases should be covered!");
 }
 
+FunctionDecl *
+ASTNodeImporter::FindFunctionTemplateSpecialization(FunctionDecl *FromFD) {
+  assert(FromFD->getTemplatedKind() ==
+         FunctionDecl::TK_FunctionTemplateSpecialization);
+  auto *FTSInfo = FromFD->getTemplateSpecializationInfo();
+  auto *Template = cast_or_null<FunctionTemplateDecl>(
+      Importer.Import(FTSInfo->getTemplate()));
+  if (!Template)
+    return nullptr;
+
+  // Import template arguments.
+  auto TemplArgs = FTSInfo->TemplateArguments->asArray();
+  SmallVector<TemplateArgument, 8> ToTemplArgs;
+  if (ImportTemplateArguments(TemplArgs.data(), TemplArgs.size(), ToTemplArgs))
+    return nullptr;
+
+  void *InsertPos = nullptr;
+  auto *FoundSpec = Template->findSpecialization(ToTemplArgs, InsertPos);
+  return FoundSpec;
+}
+
 Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
+
+  llvm::SmallVector<Decl*, 2> Redecls = getCanonicalForwardRedeclChain(D);
+  auto RedeclIt = Redecls.begin();
+  // Import the first part of the decl chain. I.e. import all previous
+  // declarations starting from the canonical decl.
+  for (;RedeclIt != Redecls.end() && *RedeclIt != D; ++RedeclIt)
+    Importer.Import(*RedeclIt);
+  assert(*RedeclIt == D);
+
   // Import the major distinguishing characteristics of this function.
   DeclContext *DC, *LexicalDC;
   DeclarationName Name;
@@ -2323,13 +2374,27 @@
   if (ToD)
     return ToD;
 
-  const FunctionDecl *FoundWithoutBody = nullptr;
-
+  const FunctionDecl *FoundByLookup = nullptr;
+
+  // If this is a function template specialization, then try to find the same
+  // existing specialization in the "to" context.  The localUncachedLookup
+  // below will not find any specialization, but would find the primary
+  // template; thus, we have to skip normal lookup in case of specializations.
+  // FIXME handle member function templates (TK_MemberSpecialization) similarly?
+  if (D->getTemplatedKind() ==
+      FunctionDecl::TK_FunctionTemplateSpecialization) {
+    if (FunctionDecl *FoundFunction = FindFunctionTemplateSpecialization(D)) {
+      if (D->doesThisDeclarationHaveABody() &&
+          FoundFunction->hasBody())
+        return Importer.Imported(D, FoundFunction);
+      FoundByLookup = FoundFunction;
+    }
+  }
   // Try to find a function in our own ("to") context with the same name, same
   // type, and in the same context as the function we're importing.
-  if (!LexicalDC->isFunctionOrMethod()) {
+  else if (!LexicalDC->isFunctionOrMethod()) {
     SmallVector<NamedDecl *, 4> ConflictingDecls;
-    unsigned IDNS = Decl::IDNS_Ordinary;
+    unsigned IDNS = Decl::IDNS_Ordinary | Decl::IDNS_OrdinaryFriend;
     SmallVector<NamedDecl *, 2> FoundDecls;
     DC->getRedeclContext()->localUncachedLookup(Name, FoundDecls);
     for (auto *FoundDecl : FoundDecls) {
@@ -2341,15 +2406,11 @@
             D->hasExternalFormalLinkage()) {
           if (Importer.IsStructurallyEquivalent(D->getType(), 
                                                 FoundFunction->getType())) {
-            // FIXME: Actually try to merge the body and other attributes.
-            const FunctionDecl *FromBodyDecl = nullptr;
-            D->hasBody(FromBodyDecl);
-            if (D == FromBodyDecl && !FoundFunction->hasBody()) {
-              // This function is needed to merge completely.
-              FoundWithoutBody = FoundFunction;
+              if (D->doesThisDeclarationHaveABody() &&
+                  FoundFunction->hasBody())
+                return Importer.Imported(D, FoundFunction);
+              FoundByLookup = FoundFunction;
               break;
-            }
-            return Importer.Imported(D, FoundFunction);
           }
 
           // FIXME: Check for overloading more carefully, e.g., by boosting
@@ -2499,9 +2560,9 @@
   }
   ToFunction->setParams(Parameters);
 
-  if (FoundWithoutBody) {
+  if (FoundByLookup) {
     auto *Recent = const_cast<FunctionDecl *>(
-          FoundWithoutBody->getMostRecentDecl());
+          FoundByLookup->getMostRecentDecl());
     ToFunction->setPreviousDecl(Recent);
   }
 
@@ -2523,10 +2584,11 @@
     ToFunction->setType(T);
   }
 
-  // Import the body, if any.
-  if (Stmt *FromBody = D->getBody()) {
-    if (Stmt *ToBody = Importer.Import(FromBody)) {
-      ToFunction->setBody(ToBody);
+  if (D->doesThisDeclarationHaveABody()) {
+    if (Stmt *FromBody = D->getBody()) {
+      if (Stmt *ToBody = Importer.Import(FromBody)) {
+        ToFunction->setBody(ToBody);
+      }
     }
   }
 
@@ -2536,14 +2598,28 @@
   if (ImportTemplateInformation(D, ToFunction))
     return nullptr;
 
-  // Add this function to the lexical context.
-  // NOTE: If the function is templated declaration, it should be not added into
-  // LexicalDC. But described template is imported during import of
-  // FunctionTemplateDecl (it happens later). So, we use source declaration
-  // to determine if we should add the result function.
-  if (!D->getDescribedFunctionTemplate())
+  bool IsFriend = D->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend);
+
+  // TODO Can we generalize this approach to other AST nodes as well?
+  if (D->getDeclContext()->containsDecl(D))
+    DC->addDeclInternal(ToFunction);
+  if (DC != LexicalDC && D->getLexicalDeclContext()->containsDecl(D))
     LexicalDC->addDeclInternal(ToFunction);
 
+  // Friend declarations lexical context is the befriending class, but the
+  // semantic context is the enclosing scope of the befriending class.
+  // We want the friend functions to be found in the semantic context by lookup.
+  // FIXME should we handle this genrically in VisitFriendDecl?
+  // In Other cases when LexicalDC != DC we don't want it to be added,
+  // e.g out-of-class definitions like void B::f() {} .
+  if (LexicalDC != DC && IsFriend) {
+    DC->makeDeclVisibleInContext(ToFunction);
+  }
+
+  // Import the rest of the chain. I.e. import all subsequent declarations.
+  for (++RedeclIt; RedeclIt != Redecls.end(); ++RedeclIt)
+    Importer.Import(*RedeclIt);
+
   if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
     ImportOverrides(cast<CXXMethodDecl>(ToFunction), FromCXXMethod);
 
Index: include/clang/AST/ASTImporter.h
===================================================================
--- include/clang/AST/ASTImporter.h
+++ include/clang/AST/ASTImporter.h
@@ -43,6 +43,15 @@
 class TypeSourceInfo;
 class Attr;
 
+  // \brief Returns with a list of declarations started from the canonical decl
+  // then followed by subsequent decls in the translation unit.
+  // This gives a canonical list for each entry in the redecl chain.
+  // `Decl::redecls()` gives a list of decls which always start from the
+  // previous decl and the next item is actually the previous item in the order
+  // of source locations.  Thus, `Decl::redecls()` gives different lists for
+  // the different entries in a given redecl chain.
+  llvm::SmallVector<Decl*, 2> getCanonicalForwardRedeclChain(Decl* D);
+
   /// Imports selected nodes from one AST context into another context,
   /// merging AST nodes where appropriate.
   class ASTImporter {
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