Report an error for dynamic evaluation of &&/|| when left operand is statically typed as an interface

src/Compilers/CSharp/Portable/Binder/Binder_Operators.cs

@@ -1632,6 +1632,13 @@ bool hasApplicableBooleanOperator(NamedTypeSymbol containingType, string name, T
                             var conversion = this.Conversions.ClassifyConversionFromType(argumentType, op.GetParameterType(0), isChecked: CheckOverflowAtRuntime, ref useSiteInfo);
                             if (conversion.IsImplicit)
                             {
+                                // Operators defined on interfaces cannot be used with dynamic binding at runtime,
+                                // so we don't consider them as applicable.
+                                if (op.ContainingType.IsInterface)
+                                {
+                                    continue;
+                                }
+
                                 @operator = op;
                                 operators.Free();
                                 return true;

src/Compilers/CSharp/Test/Semantic/Semantics/DynamicTests.cs

@@ -3649,6 +3649,99 @@ dynamic M(dynamic d)
             );
         }
 
+        [Fact]
+        public void DynamicBooleanExpression_InterfaceOperator_And()
+        {
+            const string source = @"
+interface I1
+{
+    static bool operator true(I1 x) => false;
+    static bool operator false(I1 x) => false;
+}
+
+class C1 : I1
+{
+    public static C1 operator &(C1 x, C1 y) => x;
+    public static bool operator true(C1 x) => false;
+    public static bool operator false(C1 x) => false;
+}
+
+class Test
+{
+    void M()
+    {
+        I1 x = new C1();
+        dynamic y = new C1();
+        _ = x && y;
+    }
+}";
+            CreateCompilation(source, targetFramework: TargetFramework.Net70).VerifyDiagnostics(
+                // (21,13): error CS7083: Expression must be implicitly convertible to Boolean or its type 'I1' must define operator 'false'.
+                Diagnostic(ErrorCode.ERR_InvalidDynamicCondition, "x").WithArguments("I1", "false")
+            );
+        }
+
+        [Fact]
+        public void DynamicBooleanExpression_InterfaceOperator_Or()
+        {
+            const string source = @"
+interface I1
+{
+    static bool operator true(I1 x) => false;
+    static bool operator false(I1 x) => false;
+}
+
+class C1 : I1
+{
+    public static C1 operator |(C1 x, C1 y) => x;
+    public static bool operator true(C1 x) => false;
+    public static bool operator false(C1 x) => false;
+}
+
+class Test
+{
+    void M()
+    {
+        I1 x = new C1();
+        dynamic y = new C1();
+        _ = x || y;
+    }
+}";
+            CreateCompilation(source, targetFramework: TargetFramework.Net70).VerifyDiagnostics(
+                // (21,13): error CS7083: Expression must be implicitly convertible to Boolean or its type 'I1' must define operator 'true'.
+                Diagnostic(ErrorCode.ERR_InvalidDynamicCondition, "x").WithArguments("I1", "true")
+            );
+        }
+
+        [Fact]
+        public void DynamicBooleanExpression_ClassWithoutOperator()
+        {
+            // Ensure the class case still works correctly (regression test)
+            const string source = @"
+class C0 { }
+
+class C1 : C0
+{
+    public static C1 operator &(C1 x, C1 y) => x;
+    public static bool operator true(C1 x) => false;
+    public static bool operator false(C1 x) => false;
+}
+
+class Test
+{
+    void M()
+    {
+        C0 x = new C1();
+        dynamic y = new C1();
+        _ = x && y;
+    }
+}";
+            CreateCompilation(source, targetFramework: TargetFramework.Net70).VerifyDiagnostics(
+                // (17,13): error CS7083: Expression must be implicitly convertible to Boolean or its type 'C0' must define operator 'false'.
+                Diagnostic(ErrorCode.ERR_InvalidDynamicCondition, "x").WithArguments("C0", "false")
+            );
+        }
+
         [Fact]
         public void DynamicConstructorCall1()
         {