Merge pull request #59259 from CyrusNajmabadi/populateSwitchPatternDefault

Fix 'populate switch' to understand more possible user cases

Author: CyrusNajmabadi

src/Analyzers/CSharp/Tests/PopulateSwitch/PopulateSwitchExpressionTests.cs

@@ -1261,5 +1261,111 @@ public enum E
 "
 );
         }
+
+        [Fact, WorkItem(58468, "https://github.com/dotnet/roslyn/issues/58468")]
+        public async Task NotOnOrPatternWhichAlwaysSucceeds1()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+enum Greeting
+{
+    Hello,
+    Goodbye
+};
+
+class C
+{
+    void M()
+    {
+        Greeting greeting = Greeting.Hello;
+        string message = greeting [||]switch
+        {
+            Greeting.Hello => ""Hey!"",
+            Greeting.Goodbye or _ => ""Not sure what to say 🤔""
+        };
+    }
+}
+");
+        }
+
+        [Fact, WorkItem(58468, "https://github.com/dotnet/roslyn/issues/58468")]
+        public async Task NotOnOrPatternWhichAlwaysSucceeds2()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+enum Greeting
+{
+    Hello,
+    Goodbye
+};
+
+class C
+{
+    void M()
+    {
+        Greeting greeting = Greeting.Hello;
+        string message = greeting [||]switch
+        {
+            Greeting.Hello => ""Hey!"",
+            _ or Greeting.Goodbye => ""Not sure what to say 🤔""
+        };
+    }
+}
+");
+        }
+
+        [Fact, WorkItem(58468, "https://github.com/dotnet/roslyn/issues/58468")]
+        public async Task NotOnOrPatternWhichAlwaysSucceeds3()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+enum Greeting
+{
+    Hello,
+    Goodbye
+};
+
+class C
+{
+    void M()
+    {
+        Greeting greeting = Greeting.Hello;
+        string message = greeting [||]switch
+        {
+            Greeting.Hello => ""Hey!"",
+            Greeting.Goodbye => ""Bye!"",
+            _ and var v => ""Not sure what to say 🤔""
+        };
+    }
+}
+");
+        }
+
+        [Fact, WorkItem(58468, "https://github.com/dotnet/roslyn/issues/58468")]
+        public async Task NotOnOrPatternWhichAlwaysSucceeds4()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+enum Greeting
+{
+    Hello,
+    Goodbye
+};
+
+class C
+{
+    void M()
+    {
+        Greeting greeting = Greeting.Hello;
+        string message = greeting [||]switch
+        {
+            Greeting.Hello => ""Hey!"",
+            Greeting.Goodbye => ""Bye!"",
+            var x and var y => ""Not sure what to say 🤔""
+        };
+    }
+}
+");
+        }
     }
 }

src/Analyzers/Core/Analyzers/PopulateSwitch/PopulateSwitchExpressionHelpers.cs

@@ -70,17 +70,27 @@ private static void RemoveIfConstantPatternHasValue(IOperation operation, Dictio
         }
 
         public static bool HasDefaultCase(ISwitchExpressionOperation operation)
-            => operation.Arms.Any(a => IsDefault(a));
+            => operation.Arms.Any(IsDefault);
 
         public static bool IsDefault(ISwitchExpressionArmOperation arm)
-        {
-            if (arm.Pattern.Kind == OperationKind.DiscardPattern)
-                return true;
-
-            if (arm.Pattern is IDeclarationPatternOperation declarationPattern)
-                return declarationPattern.MatchesNull;
+            => IsDefault(arm.Pattern);
 
-            return false;
-        }
+        private static bool IsDefault(IPatternOperation pattern)
+            => pattern switch
+            {
+                // _ => ...
+                IDiscardPatternOperation => true,
+                // var v => ...
+                IDeclarationPatternOperation declarationPattern => declarationPattern.MatchesNull,
+                IBinaryPatternOperation binaryPattern => binaryPattern.OperatorKind switch
+                {
+                    // x or _ => ...
+                    BinaryOperatorKind.Or => IsDefault(binaryPattern.LeftPattern) || IsDefault(binaryPattern.RightPattern),
+                    // _ and var x => ...
+                    BinaryOperatorKind.And => IsDefault(binaryPattern.LeftPattern) && IsDefault(binaryPattern.RightPattern),
+                    _ => false,
+                },
+                _ => false
+            };
     }
 }