Addresses Inspection False Positive: Issue 5456

Modifies IsResultReference(...) to avoid flagging an unused assignment that
preceeds a GoTo/Resume statement that branches execution to a
line in the procedure where the assignment could be used.

Author: BZngr

Rubberduck.CodeAnalysis/Inspections/Concrete/AssignmentNotUsedInspection.cs

@@ -5,6 +5,7 @@
 using Rubberduck.Inspections.CodePathAnalysis;
 using Rubberduck.Inspections.CodePathAnalysis.Extensions;
 using Rubberduck.Inspections.CodePathAnalysis.Nodes;
+using Rubberduck.Parsing;
 using Rubberduck.Parsing.Grammar;
 using Rubberduck.Parsing.Symbols;
 using Rubberduck.Parsing.VBA;
@@ -67,7 +68,7 @@ private IEnumerable<IdentifierReference> UnusedAssignments(Declaration localVari
             return UnusedAssignmentReferences(tree);
         }
 
-        public static List<IdentifierReference> UnusedAssignmentReferences(INode node)
+        private static List<IdentifierReference> UnusedAssignmentReferences(INode node)
         {
             var nodes = new List<IdentifierReference>();
 
@@ -98,7 +99,8 @@ public static List<IdentifierReference> UnusedAssignmentReferences(INode node)
 
         protected override bool IsResultReference(IdentifierReference reference, DeclarationFinder finder)
         {
-            return !IsAssignmentOfNothing(reference);
+            return !(IsAssignmentOfNothing(reference)
+                        || DisqualifiedByResumeOrGoToStatements(reference, finder));
         }
 
         private static bool IsAssignmentOfNothing(IdentifierReference reference)
@@ -108,6 +110,38 @@ private static bool IsAssignmentOfNothing(IdentifierReference reference)
                 && setStmtContext.expression().GetText().Equals(Tokens.Nothing);
         }
 
+        private static bool DisqualifiedByResumeOrGoToStatements(IdentifierReference resultCandidate, DeclarationFinder finder)
+        {
+            var relevantLabels = finder.DeclarationsWithType(DeclarationType.LineLabel)
+                                            .Where(label => resultCandidate.ParentScoping.Equals(label.ParentDeclaration));
+
+            if (!relevantLabels.Any())
+            {
+                return false;
+            }
+
+            var lineNumbersForNonAssignmentReferencesOfResultCandidateDeclaration = 
+                    resultCandidate.Declaration.References
+                                                    .Where(rf => !rf.IsAssignment)
+                                                    .Select(rf => rf.Context.Stop.Line);
+
+            if (!lineNumbersForNonAssignmentReferencesOfResultCandidateDeclaration.Any())
+            {
+                return false;
+            }
+
+            var labelReferencesAffectingExecutionPath = relevantLabels.SelectMany(d => d.References)
+                                .Where(labelReference => LabelReferencedByJumpStatementAfterResultCandidateAssignment(labelReference, resultCandidate));
+
+            return labelReferencesAffectingExecutionPath.Any(labelReference => labelReference.Declaration.Context.Stop.Line < resultCandidate.Context.Start.Line
+                                                && labelReference.Declaration.Context.Start.Line < lineNumbersForNonAssignmentReferencesOfResultCandidateDeclaration.Max());
+        }
+
+        private static bool LabelReferencedByJumpStatementAfterResultCandidateAssignment(IdentifierReference labelReference, IdentifierReference resultCandidate)
+            => labelReference.Context.Start.Line > resultCandidate.Context.Stop.Line
+                    && (labelReference.Context.TryGetAncestor<VBAParser.ResumeStmtContext>(out _)
+                        || labelReference.Context.TryGetAncestor<VBAParser.GoToStmtContext>(out _));
+
         protected override string ResultDescription(IdentifierReference reference)
         {
             return Description;

RubberduckTests/Inspections/AssignmentNotUsedInspectionTests.cs

@@ -259,6 +259,56 @@ Dim foo As Long
             Assert.AreEqual(0, results.Count());
         }
 
+        //https://github.com/rubberduck-vba/Rubberduck/issues/5456
+        [TestCase("Resume CleanExit")]
+        [TestCase("GoTo CleanExit")]
+        public void IgnoresAssignmentWhereExecutionPathModifiedByJumpStatementCouldIncludeUse(string statement)
+        {
+            string code =
+$@"
+Public Function Inverse(value As Double) As Double
+    Dim ratio As Double
+    ratio = 0# 'assigment not used - flagged
+On Error Goto ErrorHandler
+    ratio = 1# / value
+CleanExit:
+    Inverse = ratio
+    Exit Function
+ErrorHandler:
+    ratio = -1# 'assigment not used evaluation disqualified by Resume/GoTo - not flagged
+    {statement}
+End Function
+";
+            var results = InspectionResultsForStandardModule(code);
+            Assert.AreEqual(1, results.Count());
+        }
+
+        [TestCase("Resume IgnoreRatio")]
+        [TestCase("GoTo IgnoreRatio")]
+        public void FlagsAssignmentWhereExecutionPathModifiedByJumpStatementCouldNotIncludeUse(string statement)
+        {
+            string code =
+$@"
+Public Function Inverse(value As Double) As Double
+    Inverse = 0#
+    Dim ratio As Double
+On Error Goto ErrorHandler
+    ratio = 1# / value
+    Inverse = ratio
+
+IgnoreRatio:
+    Exit Function
+ErrorHandler:
+    'assignment not used since jump is to IgnoreRatio: 
+    'and all ratio references below IgnoreRatio: are assignments
+    ratio = 0# 
+    {statement}
+End Function
+";
+            var results = InspectionResultsForStandardModule(code);
+            Assert.AreEqual(1, results.Count());
+        }
+
         protected override IInspection InspectionUnderTest(RubberduckParserState state)
         {
             return new AssignmentNotUsedInspection(state, new Walker());