rule-of-two-soft: Honour explicitly defaulted copy-ctor/operator

The user signaled he knows what he's doing and there's even valid
use cases

BUG: 443343

src/checks/level1/rule-of-two-soft.cpp

@@ -48,7 +48,9 @@ void RuleOfTwoSoft::VisitStmt(Stmt *s)
         if (method && method->getParent() &&  method->isCopyAssignmentOperator()) {
             CXXRecordDecl *record = method->getParent();
             const bool hasCopyCtor = record->hasNonTrivialCopyConstructor();
-            const bool hasCopyAssignOp = record->hasNonTrivialCopyAssignment();
+            const bool hasCopyAssignOp = record->hasNonTrivialCopyAssignment()
+                                         || method->isExplicitlyDefaulted();
+
             if (hasCopyCtor && !hasCopyAssignOp && !isBlacklisted(record)) {
                 string msg = "Using assign operator but class " + record->getQualifiedNameAsString() + " has copy-ctor but no assign operator";
                 emitWarning(clazy::getLocStart(s), msg);
@@ -58,7 +60,8 @@ void RuleOfTwoSoft::VisitStmt(Stmt *s)
         CXXConstructorDecl *ctorDecl = ctorExpr->getConstructor();
         CXXRecordDecl *record = ctorDecl->getParent();
         if (ctorDecl->isCopyConstructor() && record) {
-            const bool hasCopyCtor = record->hasNonTrivialCopyConstructor();
+            const bool hasCopyCtor = record->hasNonTrivialCopyConstructor()
+                                     || ctorDecl->isExplicitlyDefaulted();
             const bool hasCopyAssignOp = record->hasNonTrivialCopyAssignment();
             if (!hasCopyCtor && hasCopyAssignOp && !isBlacklisted(record)) {
                 string msg = "Using copy-ctor but class " + record->getQualifiedNameAsString() + " has a trivial copy-ctor but non trivial assign operator";

tests/rule-of-two-soft/bug443343.cpp

@@ -0,0 +1,30 @@
+struct Test
+{
+    Test() {}
+    ~Test() { }
+
+    Test(const Test &) {}
+    Test& operator=(const Test&) = default;
+};
+
+void test()
+{
+    Test t;
+    Test t2;
+    t = t2; // OK, the developer explicitly says he wants the default copy-assign op
+}
+
+struct Test2
+{
+    Test2() {}
+    ~Test2() { }
+
+    Test2(const Test2 &) {}
+};
+
+void test2()
+{
+    Test2 t;
+    Test2 t2;
+    t = t2; // Warn
+}

tests/rule-of-two-soft/bug443343.cpp.expected

@@ -0,0 +1 @@
+rule-of-two-soft/bug443343.cpp:29:5: warning: Using assign operator but class Test2 has copy-ctor but no assign operator [-Wclazy-rule-of-two-soft]

tests/rule-of-two-soft/config.json

@@ -5,6 +5,9 @@
         },
         {
             "filename" : "bug375537.cpp"
+        },
+        {
+            "filename" : "bug443343.cpp"
         }
     ]
 }