5355: False postive var not assigned

Avoid false positive "variable not assigned" for

struct Fred{
};
void foo () {
  Fred fred;
  throw fred;
}

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/checkunusedvar.cpp

@@ -1126,7 +1126,7 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 unreadVariableError(usage._lastAccess, varname);
 
             // variable has been read but not written
-            else if (!usage._write && !usage._allocateMemory && !var->isStlType())
+            else if (!usage._write && !usage._allocateMemory && !var->isStlType() && !isEmptyType(var->type()))
                 unassignedVariableError(usage._var->nameToken(), varname);
         }
     }
@@ -1291,3 +1291,29 @@ bool CheckUnusedVar::isRecordTypeWithoutSideEffects(const Type* type)
     withoutSideEffects=false;   // unknown types are assumed to have side effects
     return withoutSideEffects;
 }
+
+bool CheckUnusedVar::isEmptyType(const Type* type)
+{
+    // a type that has no variables and no constructor
+
+    std::pair<std::map<const Type *,bool>::iterator,bool> found=isEmptyTypeMap.insert(
+                std::pair<const Type *,bool>(type,false));
+    bool & emptyType=found.first->second;
+    if (!found.second)
+        return emptyType;
+
+    if (type && type->classScope && type->classScope->numConstructors == 0 &&
+        (type->classScope->varlist.empty())) {
+        for (std::vector<Type::BaseInfo>::const_iterator i = type->derivedFrom.begin(); i != type->derivedFrom.end(); ++i) {
+            if (!isEmptyType(i->type)) {
+                emptyType=false;
+                return emptyType;
+            }
+        }
+        emptyType=true;
+        return emptyType;
+    }
+
+    emptyType=false;   // unknown types are assumed to be nonempty
+    return emptyType;
+}

lib/checkunusedvar.h

@@ -75,6 +75,7 @@ public:
 
 private:
     bool isRecordTypeWithoutSideEffects(const Type* type);
+    bool isEmptyType(const Type* type);
 
     // Error messages..
     void unusedStructMemberError(const Token *tok, const std::string &structname, const std::string &varname);
@@ -110,6 +111,9 @@ private:
     }
 
     std::map<const Type *,bool> isRecordTypeWithoutSideEffectsMap;
+
+    std::map<const Type *,bool> isEmptyTypeMap;
+
 };
 /// @}
 //---------------------------------------------------------------------------

test/testunusedvar.cpp

@@ -34,6 +34,9 @@ public:
 
 private:
     void run() {
+        TEST_CASE(emptyclass);  // #5355 - False positive: Variable is not assigned a value.
+        TEST_CASE(emptystruct);  // #5355 - False positive: Variable is not assigned a value.
+
         TEST_CASE(structmember1);
         TEST_CASE(structmember2);
         TEST_CASE(structmember3);
@@ -175,6 +178,30 @@ private:
         checkUnusedVar.checkStructMemberUsage();
     }
 
+    // #5355 - False positive: Variable is not assigned a value.
+    void emptyclass() {
+        functionVariableUsage("class Carla {\n"
+                              "};\n"
+                              "class Fred : Carla {\n"
+                              "};\n"
+                              "void foo() {\n"
+                              "    Fred fred;\n"
+                              "    throw fred;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
+    // #5355 - False positive: Variable is not assigned a value.
+    void emptystruct() {
+        functionVariableUsage("struct Fred {\n"
+                              "};\n"
+                              "void foo() {\n"
+                              "    Fred fred;\n"
+                              "    throw fred;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void structmember1() {
         checkStructMemberUsage("struct abc\n"
                                "{\n"