Detect assignments to FlowCaptureReference operations

analyzers/its/expected/CSharpLatest/S1854-CSharpLatest-net8.0.json

@@ -1,5 +1,11 @@
 {
   "Issues": [
+    {
+      "Id": "S1854",
+      "Message": "Remove this useless assignment to local variable \u0027person\u0027.",
+      "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/CSharpLatest/CSharpLatest/CSharp11Features/RequiredMembers.cs#L20",
+      "Location": "Line 20 Position 9-51"
+    },
     {
       "Id": "S1854",
       "Message": "Remove this useless assignment to local variable \u0027a\u0027.",
@@ -35,6 +41,18 @@
       "Message": "Remove this useless assignment to local variable \u0027result\u0027.",
       "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/CSharpLatest/CSharpLatest/CSharp9Features/S2437.cs#L10",
       "Location": "Line 10 Position 9-30"
+    },
+    {
+      "Id": "S1854",
+      "Message": "Remove this useless assignment to local variable \u0027a\u0027.",
+      "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/CSharpLatest/CSharpLatest/CSharp9Features/S3240.cs#L12",
+      "Location": "Line 12 Position 9-32"
+    },
+    {
+      "Id": "S1854",
+      "Message": "Remove this useless assignment to local variable \u0027y\u0027.",
+      "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/CSharpLatest/CSharpLatest/CSharp9Features/S3440.cs#L8-L12",
+      "Location": "Lines 8-12 Position 9-10"
     }
   ]
 }

analyzers/its/expected/akka.net/S1854-Akka-netstandard2.0.json

@@ -1,5 +1,11 @@
 {
   "Issues": [
+    {
+      "Id": "S1854",
+      "Message": "Remove this useless assignment to local variable \u0027sender\u0027.",
+      "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/akka.net/src/core/Akka/Actor/Futures.cs#L353",
+      "Location": "Line 353 Position 13-50"
+    },
     {
       "Id": "S1854",
       "Message": "Remove this useless assignment to local variable \u0027actor\u0027.",

analyzers/src/SonarAnalyzer.CFG/LiveVariableAnalysis/RoslynLiveVariableAnalysis.cs

@@ -48,15 +48,16 @@ public RoslynLiveVariableAnalysis(ControlFlowGraph cfg, CancellationToken cancel
         Analyze();
     }
 
-    public ISymbol ParameterOrLocalSymbol(IOperation operation)
+    public IEnumerable<ISymbol> ParameterOrLocalSymbols(IOperation operation)
     {
-        ISymbol candidate = operation switch
+        var candidates = operation switch
         {
-            _ when operation.AsParameterReference() is { } parameterReference => parameterReference.Parameter,
-            _ when operation.AsLocalReference() is { } localReference => localReference.Local,
-            _ => null
+            _ when operation.AsParameterReference() is { } parameterReference => [parameterReference.Parameter],
+            _ when operation.AsLocalReference() is { } localReference => [localReference.Local],
+            _ when operation.AsFlowCaptureReference() is { } flowCaptureReference => flowCaptures.TryGetValue(flowCaptureReference.Id, out var symbols) ? symbols : [],
+            _ => []
         };
-        return IsLocal(candidate) ? candidate : null;
+        return candidates.Where(x => IsLocal(x));
     }
 
     public override bool IsLocal(ISymbol symbol) =>
@@ -90,15 +91,15 @@ private void ResolveCaptures()
             if (flowCapture.Value.AsFlowCaptureReference() is { } captureReference
                 && flowCaptures.TryGetValue(captureReference.Id, out var symbols))
             {
-                AppendFlowCaptureReference(flowCapture.Id, symbols.ToArray());
+                AppendFlowCaptureReference(flowCapture.Id, symbols);
             }
-            else if (ParameterOrLocalSymbol(flowCapture.Value) is { } symbol)
+            else
             {
-                AppendFlowCaptureReference(flowCapture.Id, symbol);
+                AppendFlowCaptureReference(flowCapture.Id, ParameterOrLocalSymbols(flowCapture.Value));
             }
         }
 
-        void AppendFlowCaptureReference(CaptureId id, params ISymbol[] symbols)
+        void AppendFlowCaptureReference(CaptureId id, IEnumerable<ISymbol> symbols)
         {
             if (!flowCaptures.TryGetValue(id, out var list))
             {
@@ -281,27 +282,23 @@ private void ProcessOperation(ControlFlowGraph cfg, IOperation operation)
 
         private void ProcessParameterOrLocalReference(IOperationWrapper reference)
         {
-            if (owner.ParameterOrLocalSymbol(reference.WrappedOperation) is { } symbol)
+            var symbols = owner.ParameterOrLocalSymbols(reference.WrappedOperation);
+            if (reference.IsOutArgument())
             {
-                if (reference.IsOutArgument())
-                {
-                    Assigned.Add(symbol);
-                    UsedBeforeAssigned.Remove(symbol);
-                }
-                else if (!reference.IsAssignmentTarget())
-                {
-                    UsedBeforeAssigned.Add(symbol);
-                }
+                Assigned.UnionWith(symbols);
+                UsedBeforeAssigned.ExceptWith(symbols);
+            }
+            else if (!reference.IsAssignmentTarget())
+            {
+                UsedBeforeAssigned.UnionWith(symbols);
             }
         }
 
         private void ProcessSimpleAssignment(ISimpleAssignmentOperationWrapper assignment)
         {
-            if (owner.ParameterOrLocalSymbol(assignment.Target) is { } localTarget)
-            {
-                Assigned.Add(localTarget);
-                UsedBeforeAssigned.Remove(localTarget);
-            }
+            var targets = owner.ParameterOrLocalSymbols(assignment.Target);
+            Assigned.UnionWith(targets);
+            UsedBeforeAssigned.ExceptWith(targets);
         }
 
         private void ProcessFlowAnonymousFunction(ControlFlowGraph cfg, IFlowAnonymousFunctionOperationWrapper anonymousFunction)
@@ -316,9 +313,10 @@ private void ProcessCaptured(ControlFlowGraph cfg)
         {
             foreach (var operation in cfg.Blocks.SelectMany(x => x.OperationsAndBranchValue).SelectMany(x => x.DescendantsAndSelf()))
             {
-                if (owner.ParameterOrLocalSymbol(operation) is { } symbol)
+                var symbols = owner.ParameterOrLocalSymbols(operation);
+                if (symbols.Any())
                 {
-                    Captured.Add(symbol);
+                    Captured.UnionWith(symbols);
                 }
                 else
                 {

analyzers/src/SonarAnalyzer.CSharp/Rules/DeadStores.RoslynCfg.cs

@@ -73,25 +73,21 @@ public override void AnalyzeBlock()
 
                 private void ProcessParameterOrLocalReference(IOperationWrapper reference)
                 {
-                    if (owner.lva.ParameterOrLocalSymbol(reference.WrappedOperation) is { } symbol && IsSymbolRelevant(symbol))
+                    var symbols = owner.lva.ParameterOrLocalSymbols(reference.WrappedOperation).Where(x => IsSymbolRelevant(x));
+                    if (reference.IsOutArgument())
                     {
-                        if (reference.IsOutArgument())
-                        {
-                            liveOut.Remove(symbol);
-                        }
-                        else if (!reference.IsAssignmentTarget() && !reference.IsCompoundAssignmentTarget())
-                        {
-                            liveOut.Add(symbol);
-                        }
+                        liveOut.ExceptWith(symbols);
+                    }
+                    else if (!reference.IsAssignmentTarget() && !reference.IsCompoundAssignmentTarget())
+                    {
+                        liveOut.UnionWith(symbols);
                     }
                 }
 
                 private void ProcessSimpleAssignment(ISimpleAssignmentOperationWrapper assignment)
                 {
-                    if (ProcessAssignment(assignment, assignment.Target, assignment.Value) is { } localTarget)
-                    {
-                        liveOut.Remove(localTarget);
-                    }
+                    var targets = ProcessAssignment(assignment, assignment.Target, assignment.Value);
+                    liveOut.ExceptWith(targets);
                 }
 
                 private void ProcessCompoundAssignment(ICompoundAssignmentOperationWrapper assignment) =>
@@ -106,43 +102,38 @@ private void ProcessDeconstructionAssignment(IDeconstructionAssignmentOperationW
                     {
                         foreach (var tupleElement in ITupleOperationWrapper.FromOperation(deconstructionAssignment.Target).AllElements())
                         {
-                            if (ProcessAssignment(deconstructionAssignment, tupleElement) is { } target)
-                            {
-                                liveOut.Remove(target);
-                            }
+                            var targets = ProcessAssignment(deconstructionAssignment, tupleElement);
+                            liveOut.ExceptWith(targets);
                         }
                     }
                 }
 
-                private ISymbol ProcessAssignment(IOperationWrapper operation, IOperation target, IOperation value = null)
+                private ISymbol[] ProcessAssignment(IOperationWrapper operation, IOperation target, IOperation value = null)
                 {
-                    if (owner.lva.ParameterOrLocalSymbol(target) is { } localTarget && IsSymbolRelevant(localTarget))
+                    var targets = owner.lva.ParameterOrLocalSymbols(target).Where(IsSymbolRelevant).ToArray();
+                    foreach (var localTarget in targets)
                     {
-                        if (TargetRefKind() == RefKind.None
-                            && !IsConst()
+                        if (TargetRefKind(localTarget) == RefKind.None
+                            && !IsConst(localTarget)
                             && !liveOut.Contains(localTarget)
-                            && !IsAllowedInitialization()
+                            && !IsAllowedInitialization(localTarget)
                             && !ICaughtExceptionOperationWrapper.IsInstance(value)
                             && !target.Syntax.Parent.IsKind(SyntaxKind.ForEachStatement)
                             && !IsMuted(target.Syntax, localTarget))
                         {
                             ReportIssue(operation.WrappedOperation.Syntax.GetLocation(), localTarget);
                         }
-                        return localTarget;
-                    }
-                    else
-                    {
-                        return null;
                     }
+                    return targets;
 
-                    bool IsConst() =>
+                    static bool IsConst(ISymbol localTarget) =>
                         localTarget is ILocalSymbol local && local.IsConst;
 
-                    RefKind TargetRefKind() =>
+                    static RefKind TargetRefKind(ISymbol localTarget) =>
                         // Only ILocalSymbol and IParameterSymbol can be returned by ParameterOrLocalSymbol
                         localTarget is ILocalSymbol local ? local.RefKind() : ((IParameterSymbol)localTarget).RefKind;
 
-                    bool IsAllowedInitialization() =>
+                    bool IsAllowedInitialization(ISymbol localTarget) =>
                         operation.WrappedOperation.Syntax is VariableDeclaratorSyntax variableDeclarator
                         && variableDeclarator.Initializer != null
                         // Avoid collision with S1481: Unused is allowed. Used only in local function is also unused in current CFG.

analyzers/src/SonarAnalyzer.CSharp/Rules/DeadStores.cs

@@ -57,6 +57,7 @@ protected override void Initialize(SonarAnalysisContext context)
                 SyntaxKind.OperatorDeclaration,
                 SyntaxKind.RemoveAccessorDeclaration,
                 SyntaxKind.SetAccessorDeclaration,
+                SyntaxKindEx.CoalesceAssignmentExpression,
                 SyntaxKindEx.InitAccessorDeclaration,
                 SyntaxKindEx.LocalFunctionStatement);
 

analyzers/tests/SonarAnalyzer.Test/TestCases/DeadStores.RoslynCfg.cs

@@ -302,7 +302,7 @@ public void Assignment(DeadStores sender)
             string coa = SomeString();
             coa ??= SomeString();
             Use(coa);
-            coa ??= SomeString();  // Roslyn CFG FN: Branching with FlowCaptureOperation
+            coa ??= SomeString();  // Noncompliant
         }
 
         public void Unary()
@@ -650,9 +650,9 @@ private void ConditionalEvaluation(bool b1, bool b2, object coalesce, object coa
             var x = false;  // Compliant ignored value
             x = true;       // Roslyn CFG FN: Consequence of inaccurate LVA state below
             x = b1 && b2;   // Roslyn CFG FN: Branching with FlowCaptureOperation
-            x = b1 || b2;   // Roslyn CFG FN: Branching with FlowCaptureOperation
-            coalesce = coalesce ?? "Value";   // Roslyn CFG FN: Branching with FlowCaptureOperation
-            coalesceAssignment ??= "Value";   // Roslyn CFG FN: Branching with FlowCaptureOperation
+            x = b1 || b2;   // Noncompliant
+            coalesce = coalesce ?? "Value";   // Noncompliant
+            coalesceAssignment ??= "Value";   // Noncompliant
         }
 
         private void SimpleAssignment()
@@ -776,7 +776,7 @@ int[] Compute(int[] arr)
                 var lst = arr;    //Compliant
                 var unused = arr;
                 lst ??= new int[0];
-                unused ??= new int[0];  // Roslyn CFG FN: Branching with FlowCaptureOperation
+                unused ??= new int[0];  // Noncompliant
                 return lst;
             }
         }