From 6dda3588936be386e575f9874f111899c6ccf122 Mon Sep 17 00:00:00 2001
From: Zsolt Kolbay
 <121798625+zsolt-kolbay-sonarsource@users.noreply.github.com>
Date: Wed, 20 Dec 2023 13:11:46 +0100
Subject: [PATCH] Fix S2589 FP: Discard pattern in switch statement (#8485)

---
 .../Roslyn/Extensions/IOperationExtensions.cs |  3 ++
 .../ConditionEvaluatesToConstantBase.cs       | 10 ++--
 .../ConditionEvaluatesToConstant.CSharp9.cs   | 49 ++++++++++++++-----
 3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/Extensions/IOperationExtensions.cs b/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/Extensions/IOperationExtensions.cs
index 0e9119f27ac..688773207cb 100644
--- a/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/Extensions/IOperationExtensions.cs
+++ b/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/Extensions/IOperationExtensions.cs
@@ -72,6 +72,9 @@ OperationKindEx.PropertyReference when operation.ToPropertyReference() is { Prop
     internal static IPropertyReferenceOperationWrapper? AsPropertyReference(this IOperation operation) =>
         operation.As(OperationKindEx.PropertyReference, IPropertyReferenceOperationWrapper.FromOperation);
 
+    internal static IRecursivePatternOperationWrapper? AsRecursivePattern(this IOperation operation) =>
+        operation.As(OperationKindEx.RecursivePattern, IRecursivePatternOperationWrapper.FromOperation);
+
     internal static ITupleOperationWrapper? AsTuple(this IOperation operation) =>
         operation.As(OperationKindEx.Tuple, ITupleOperationWrapper.FromOperation);
 
diff --git a/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/RuleChecks/ConditionEvaluatesToConstantBase.cs b/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/RuleChecks/ConditionEvaluatesToConstantBase.cs
index 8281b2ef6d0..4d66fd98c7e 100644
--- a/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/RuleChecks/ConditionEvaluatesToConstantBase.cs
+++ b/analyzers/src/SonarAnalyzer.Common/SymbolicExecution/Roslyn/RuleChecks/ConditionEvaluatesToConstantBase.cs
@@ -75,16 +75,18 @@ public override ProgramState ConditionEvaluated(SymbolicContext context)
     private bool IsIgnored(ProgramState state, IOperation operation) =>
         operation.Kind is OperationKindEx.Literal
         || IsVarPattern(operation)
-        || IsDiscardPattern(operation)
+        || IsDiscardPattern(state, operation)
         || operation.TrackedSymbol(state) is IFieldSymbol { IsConst: true }
         || operation.Syntax.Ancestors().Any(x => IsInsideUsingDeclaration(x) || IsLockStatement(x));
 
     private static bool IsVarPattern(IOperation operation) =>
         operation.AsIsPattern()?.Pattern.WrappedOperation.AsDeclarationPattern()?.MatchesNull is true;
 
-    private static bool IsDiscardPattern(IOperation operation) =>
-        operation.AsIsPattern() is { } pattern
-        && pattern.Pattern.WrappedOperation.Kind is OperationKindEx.DiscardPattern;
+    private static bool IsDiscardPattern(ProgramState state, IOperation operation) =>
+        operation.Kind is OperationKindEx.DiscardPattern
+        || (operation.AsIsPattern() is { } isPattern
+            && (isPattern.Pattern.WrappedOperation.Kind is OperationKindEx.DiscardPattern
+                || (isPattern.Pattern.WrappedOperation.AsRecursivePattern() is {} recursivePattern && recursivePattern.DeconstructionSubpatterns.All(x => IsDiscardPattern(state, x)))));
 
     public override void ExecutionCompleted()
     {
diff --git a/analyzers/tests/SonarAnalyzer.UnitTest/TestCases/SymbolicExecution/Roslyn/ConditionEvaluatesToConstant.CSharp9.cs b/analyzers/tests/SonarAnalyzer.UnitTest/TestCases/SymbolicExecution/Roslyn/ConditionEvaluatesToConstant.CSharp9.cs
index 2b33b3831d0..a851f0bee43 100644
--- a/analyzers/tests/SonarAnalyzer.UnitTest/TestCases/SymbolicExecution/Roslyn/ConditionEvaluatesToConstant.CSharp9.cs
+++ b/analyzers/tests/SonarAnalyzer.UnitTest/TestCases/SymbolicExecution/Roslyn/ConditionEvaluatesToConstant.CSharp9.cs
@@ -269,22 +269,49 @@ var value when value.HasFlag(Flags.Bar) => 2,   // Compliant
 }
 
 // https://github.com/SonarSource/sonar-dotnet/issues/8008
-namespace Repro_8008
+public class Repro_8008
 {
-    class Person
+    public int Compare(string name1, string name2) => (name1, name2) switch
     {
-        public int? Age { get; set; }
-    }
+        (null, null) => 0,
+        (null, _) => 1,
+        (_, null) => -1,
+        (_, _) => Comparer<string>.Default.Compare(name1, name2)
+    };
+
+    public int NestedTuples(string name1, string name2, string name3) => ((name1, name2), name3) switch
+    {
+        ((null, null), null) => 42,
+        ((null, null), _) => 43,
+        ((_, _), null) => 44,
+        ((_, _), _) => 45
+    };
+
+    public int DeeperNestedTuples(string name1, string name2, string name3, string name4) => (((name1, name2), name3), name4) switch
+    {
+        (((null, null), null), null) => 42,
+        (((_, _), null), null) => 43,
+        (((_, _), _), null) => 44,
+        (((_, _), _), _) => 45,
+    };
 
-    class Double_Wildcard_FP
+    public int TupleWithKnownNullConstraint()
     {
-        public int Compare(Person x, Person y) => (x.Age, y.Age) switch
+        string name1 = null;
+        string name2 = null;
+        return (name1, name2) switch
         {
-            (null, null) => 0,
-            (null, _) => 1,
-            (_, null) => -1,
-            (_, _) => Comparer<int>.Default.Compare(x.Age.Value, y.Age.Value) // Noncompliant {{Change this condition so that it does not always evaluate to 'True'.}}
-          //^^^^^^
+            (null, null) => 0,  // FN
+            (null, _) => 1,     // FN
+            (_, null) => -1,    // FN
+            (_, _) => Comparer<string>.Default.Compare(name1, name2)
         };
     }
+
+    public int TupleWithDeclaration(string name1, string name2) =>
+        (name1, name2) switch
+        {
+            ("A", "B") => 0,
+            (var x, _) => -1,    // Noncompliant - FP
+        };
 }