extended ByRefAssignment logic to UnassignedVariableUsage inspection

Author: retailcoder

Rubberduck.CodeAnalysis/Inspections/Concrete/UnassignedVariableUsageInspection.cs

@@ -41,7 +41,7 @@ protected override IEnumerable<IInspectionResult> DoGetInspectionResults()
 
             return declarations
                 .Where(d => d.References.Any() && !excludedDeclarations.Any(excl => DeclarationReferencesContainsReference(excl, d)))
-                .SelectMany(d => d.References)
+                .SelectMany(d => d.References.Where(r => !IsAssignedByRefArgument(r.ParentScoping, r)))
                 .Distinct()
                 .Where(r => !r.IsIgnoringInspectionResultFor(AnnotationName))
                 .Where(r => !r.Context.TryGetAncestor<VBAParser.RedimStmtContext>(out _) && !IsArraySubscriptAssignment(r))
@@ -51,6 +51,17 @@ protected override IEnumerable<IInspectionResult> DoGetInspectionResults()
                     r)).ToList();
         }
 
+        private bool IsAssignedByRefArgument(Declaration enclosingProcedure, IdentifierReference reference)
+        {
+            var argExpression = reference.Context.GetAncestor<VBAParser.ArgumentExpressionContext>();
+            var parameter = State.DeclarationFinder.FindParameterFromArgument(argExpression, enclosingProcedure);
+
+            // note: not recursive, by design.
+            return parameter != null
+                   && (parameter.IsImplicitByRef || parameter.IsByRef)
+                   && parameter.References.Any(r => r.IsAssignment);
+        }
+
         private static bool IsArraySubscriptAssignment(IdentifierReference reference)
         {
             var isLetAssignment = reference.Context.TryGetAncestor<VBAParser.LetStmtContext>(out var letStmt);

RubberduckTests/Inspections/UnassignedVariableUsageInspectionTests.cs

@@ -12,9 +12,9 @@ namespace RubberduckTests.Inspections
     [TestFixture]
     public class UnassignedVariableUsageInspectionTests
     {
-        private IEnumerable<IInspectionResult> GetInspectionResults(string code)
+        private IEnumerable<IInspectionResult> GetInspectionResults(string code, ComponentType componentType = ComponentType.ClassModule)
         {
-            var vbe = MockVbeBuilder.BuildFromSingleModule(code, ComponentType.ClassModule, out _);
+            var vbe = MockVbeBuilder.BuildFromSingleModule(code, componentType, out _);
             using (var state = MockParser.CreateAndParse(vbe.Object))
             {
 
@@ -132,6 +132,25 @@ End Sub
             Assert.AreEqual(0, results.Count());
         }
 
+        [Test]
+        [Category("Inspections")]
+        public void UnassignedVariableUsage_NoResultForAssignedByRefReference()
+        {
+            const string code = @"
+Sub DoSomething()
+    Dim foo
+    AssignThing foo
+    Debug.Print foo
+End Sub
+
+Sub AssignThing(ByRef thing As Variant)
+    thing = 42
+End Sub
+";
+            var results = GetInspectionResults(code, ComponentType.StandardModule);
+            Assert.AreEqual(0, results.Count());
+        }
+
         [Test]
         [Category("Inspections")]
         public void UnassignedVariableUsage_NoResultIfNoReferences()