[include-fixer] do not index friend function declaration.

[ioeric]

Summary

we want to exclude friend declaration, but the DeclContext of a
friend function declaration is not the class in which it is declared, so we need
to explicitly check if the parent is a friendDecl.

[bkramer]

Makes sense.

include-fixer/find-all-symbols/FindAllSymbols.cpp

void FindAllSymbols::registerMatchers(MatchFinder *MatchFinder) {
 
   // Matchers for C++ record declarations.
   auto CxxRecordDecl =
       cxxRecordDecl(CommonFilter, CCMatcher, isDefinition(),
                     unless(isExplicitTemplateSpecialization()));
   MatchFinder->addMatcher(CxxRecordDecl.bind("decl"), this);
 
   // Matchers for function declarations.
-  MatchFinder->addMatcher(
-      functionDecl(CommonFilter, anyOf(ExternCMatcher, CCMatcher)).bind("decl"),
+  // We want to exclude friend declaration, but the `DeclContext` of a friend
+  // function declaration is not the class in which it is declared, so we need
+  // to explicitly check if the parent is a `friendDecl`.
+  MatchFinder->addMatcher(functionDecl(CommonFilter,
+                                       unless(hasParent(friendDecl())),
+                                       anyOf(ExternCMatcher, CCMatcher))
+                              .bind("decl"),
                           this);
 
   // Matcher for typedef and type alias declarations.
   //
   // typedef and type alias can come from C-style headers and C++ heaeders.
   // For C-style header, `DeclContxet` can be either `TranslationUnitDecl`
   // or `LinkageSpecDecl`.
   // For C++ header, `DeclContext ` can be one of `TranslationUnitDecl`,
   // `NamespaceDecl`.

unittests/include-fixer/find-all-symbols/FindAllSymbolsTests.cpp

TEST_F(FindAllSymbolsTest, MacroTestWithIWYU) {
 
   Symbol = SymbolInfo("Y", SymbolInfo::SymbolKind::Macro, "bar.h", 4, {});
   EXPECT_TRUE(hasSymbol(Symbol));
 
   Symbol = SymbolInfo("MAX", SymbolInfo::SymbolKind::Macro, "bar.h", 5, {});
   EXPECT_TRUE(hasSymbol(Symbol));
 }
 
+TEST_F(FindAllSymbolsTest, NoFriendTest) {
+  static const char Code[] = R"(
+    class WorstFriend {
+      friend void Friend();
+      friend class BestFriend;
+    };
+  )";
+  runFindAllSymbols(Code);
+  SymbolInfo Symbol = SymbolInfo("WorstFriend", SymbolInfo::SymbolKind::Class,
+                                 HeaderName, 2, {});
+  EXPECT_TRUE(hasSymbol(Symbol));
+
+  Symbol = SymbolInfo("Friend", SymbolInfo::SymbolKind::Function, HeaderName,
+                      3, {});
+  EXPECT_FALSE(hasSymbol(Symbol));
+
+  Symbol = SymbolInfo("BestFriend", SymbolInfo::SymbolKind::Class, HeaderName,
+                      4, {});
+  EXPECT_FALSE(hasSymbol(Symbol));
+}
+
 } // namespace find_all_symbols
 } // namespace clang