[Cxx-Interop] Enable Record Friend functions (#59801)

* Update ImportDecl to handle Friend functions inside of recrods

* Add tests and update comment

* Undo unnecessary lines, format

* Clean up and fix tests

* New approach

* Only import valid friend functions for now

* Re-add == func to get Equatable conformance

* Remove requirement that friend is a function

Author: Huddie

lib/ClangImporter/ImportDecl.cpp

@@ -2116,6 +2116,15 @@ namespace {
           continue;
         }
 
+        if (auto friendDecl = dyn_cast<clang::FriendDecl>(m)) {
+          if (friendDecl->getFriendDecl()) {
+            m = friendDecl->getFriendDecl();
+            auto lookupTable = Impl.findLookupTable(m->getOwningModule());
+            addEntryToLookupTable(*lookupTable, friendDecl->getFriendDecl(),
+                                  Impl.getNameImporter());
+          }
+        }
+
         auto nd = dyn_cast<clang::NamedDecl>(m);
         if (!nd) {
           // We couldn't import the member, so we can't reference it in Swift.
@@ -2145,6 +2154,7 @@ namespace {
         }
 
         Decl *member = Impl.importDecl(nd, getActiveSwiftVersion());
+
         if (!member) {
           if (!isa<clang::TypeDecl>(nd) && !isa<clang::FunctionDecl>(nd)) {
             // We don't know what this member is.
@@ -4764,12 +4774,6 @@ namespace {
       return nullptr;
     }
 
-    Decl *VisitFriendDecl(const clang::FriendDecl *decl) {
-      // Friends are not imported; Swift has a different access control
-      // mechanism.
-      return nullptr;
-    }
-
     Decl *VisitFriendTemplateDecl(const clang::FriendTemplateDecl *decl) {
       // Friends are not imported; Swift has a different access control
       // mechanism.

test/Interop/Cxx/operators/Inputs/member-inline.h

@@ -21,6 +21,16 @@ struct LoadableIntWrapper {
     value++;
     return *this;
   }
+
+  // Friend functions
+  friend bool operator==(const LoadableIntWrapper lhs,
+                         const LoadableIntWrapper &rhs) {
+    return lhs.value == rhs.value;
+  }
+
+  friend LoadableIntWrapper operator-(const LoadableIntWrapper& obj) {
+    return LoadableIntWrapper{.value = -obj.value};
+  }
 };
 
 struct LoadableBoolWrapper {

test/Interop/Cxx/operators/member-inline.swift

@@ -30,6 +30,21 @@ OperatorsTestSuite.test("AddressOnlyIntWrapper.minus") {
 }
 #endif
 
+OperatorsTestSuite.test("LoadableIntWrapper.equal (inline)") {
+  let lhs = LoadableIntWrapper(value: 42)
+  let rhs = LoadableIntWrapper(value: 42)
+
+  let result = lhs == rhs
+
+  expectTrue(result)
+}
+
+OperatorsTestSuite.test("LoadableIntWrapper.unaryMinus (inline)") {
+  let lhs = LoadableIntWrapper(value: 42)
+  let inverseLhs = -lhs;
+  expectEqual(-42, inverseLhs.value)
+}
+
 OperatorsTestSuite.test("LoadableIntWrapper.call (inline)") {
   var wrapper = LoadableIntWrapper(value: 42)