Convert operand of true/false operator invoked as part of &&/||operator evaluation

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

@@ -1156,17 +1156,36 @@ private BoundExpression BindConditionalLogicalOperator(BinaryExpressionSyntax no
                             CheckConstraintLanguageVersionAndRuntimeSupportForOperator(node, kind == BinaryOperatorKind.LogicalAnd ? falseOperator : trueOperator,
                                 isUnsignedRightShift: false, signature.ConstrainedToTypeOpt, diagnostics);
 
+                        var operandPlaceholder = new BoundValuePlaceholder(resultLeft.Syntax, resultLeft.Type).MakeCompilerGenerated();
+                        var trueFalseParameterType = (resultKind.Operator() == BinaryOperatorKind.And ? falseOperator : trueOperator).Parameters[0].Type;
+                        CompoundUseSiteInfo<AssemblySymbol> useSiteInfo = GetNewCompoundUseSiteInfo(diagnostics);
+                        var conversion = this.Conversions.ClassifyConversionFromType(resultLeft.Type, trueFalseParameterType, isChecked: CheckOverflowAtRuntime, ref useSiteInfo);
+                        Debug.Assert(conversion.IsImplicit);
+
+                        BoundExpression operandConversion = CreateConversion(
+                            resultLeft.Syntax,
+                            operandPlaceholder,
+                            conversion,
+                            isCast: false,
+                            conversionGroupOpt: null,
+                            trueFalseParameterType,
+                            diagnostics);
+
+                        diagnostics.Add(operandConversion.Syntax, useSiteInfo);
+
                         return new BoundUserDefinedConditionalLogicalOperator(
                             node,
                             resultKind,
-                            resultLeft,
-                            resultRight,
                             signature.Method,
                             trueOperator,
                             falseOperator,
+                            operandPlaceholder,
+                            operandConversion,
                             signature.ConstrainedToTypeOpt,
                             lookupResult,
                             originalUserDefinedOperators,
+                            resultLeft,
+                            resultRight,
                             signature.ReturnType);
                     }
                     else
@@ -1234,8 +1253,35 @@ private bool IsValidDynamicCondition(BoundExpression left, bool isNegative, Bind
                 return false;
             }
 
+            // Strictly speaking, we probably should be digging through nullable type here to look for an operator
+            // declared by the underlying type. However, it doesn't look like dynamic binder is able to deal with
+            // nullable types while evaluating logical binary operators. Exceptions that it throws look like:
+            //
+            // Microsoft.CSharp.RuntimeBinder.RuntimeBinderException : The type ('S1?') must contain declarations of operator true and operator false
+            // Stack Trace:
+            //     at CallSite.Target(Closure, CallSite, Object, Object)
+            //     at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
+            //
+            // Microsoft.CSharp.RuntimeBinder.RuntimeBinderException : Operator '&&' cannot be applied to operands of type 'S1' and 'S1?'
+            // Stack Trace:
+            //     at CallSite.Target(Closure, CallSite, Object, Nullable`1)
+            //     at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
             var namedType = type as NamedTypeSymbol;
             var result = HasApplicableBooleanOperator(namedType, isNegative ? WellKnownMemberNames.FalseOperatorName : WellKnownMemberNames.TrueOperatorName, type, ref useSiteInfo, out userDefinedOperator);
+
+            if (result)
+            {
+                Debug.Assert(userDefinedOperator is not null);
+
+                var operandPlaceholder = new BoundValuePlaceholder(left.Syntax, left.Type).MakeCompilerGenerated();
+                TypeSymbol parameterType = userDefinedOperator.Parameters[0].Type;
+
+                implicitConversion = this.Conversions.ClassifyConversionFromType(operandPlaceholder.Type, parameterType, isChecked: CheckOverflowAtRuntime, ref useSiteInfo);
+                Debug.Assert(implicitConversion.IsImplicit);
+
+                CreateConversion(left.Syntax, operandPlaceholder, implicitConversion, isCast: false, conversionGroupOpt: null, parameterType, diagnostics);
+            }
+
             diagnostics.Add(left.Syntax, useSiteInfo);
 
             return result;

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -501,6 +501,15 @@
     <Field Name="LogicalOperator" Type="MethodSymbol"/>
     <Field Name="TrueOperator" Type="MethodSymbol"/>
     <Field Name="FalseOperator" Type="MethodSymbol"/>
+
+    <!-- Used as an operand to bind TrueFalseOperandConversion -->
+    <Field Name="TrueFalseOperandPlaceholder" Type="BoundValuePlaceholder?" SkipInVisitor="true" Null="allow"/>
+    <!--
+    Could be a BoundConversion or, in some cases of an identity conversion, the OperandPlaceholder, or null for no conversion case
+    If the node survives lowering, this property in it must be null.
+    -->
+    <Field Name="TrueFalseOperandConversion" Type="BoundExpression?" SkipInVisitor="true" Null="allow"/>
+
     <Field Name="ConstrainedToTypeOpt" Type="TypeSymbol?" Null="allow"/>
     <Field Name="ResultKind" PropertyOverrides="true" Type="LookupResultKind"/>
     <!--The set of method symbols from which this operator's method was chosen.

src/Compilers/CSharp/Portable/BoundTree/Constructors.cs

@@ -454,39 +454,6 @@ public BoundBinaryOperator Update(UncommonData uncommonData)
         }
     }
 
-    internal sealed partial class BoundUserDefinedConditionalLogicalOperator
-    {
-        public BoundUserDefinedConditionalLogicalOperator(
-            SyntaxNode syntax,
-            BinaryOperatorKind operatorKind,
-            BoundExpression left,
-            BoundExpression right,
-            MethodSymbol logicalOperator,
-            MethodSymbol trueOperator,
-            MethodSymbol falseOperator,
-            TypeSymbol? constrainedToTypeOpt,
-            LookupResultKind resultKind,
-            ImmutableArray<MethodSymbol> originalUserDefinedOperatorsOpt,
-            TypeSymbol type,
-            bool hasErrors = false)
-            : this(
-                syntax,
-                operatorKind,
-                logicalOperator,
-                trueOperator,
-                falseOperator,
-                constrainedToTypeOpt,
-                resultKind,
-                originalUserDefinedOperatorsOpt,
-                left,
-                right,
-                type,
-                hasErrors)
-        {
-            Debug.Assert(operatorKind.IsUserDefined() && operatorKind.IsLogical());
-        }
-    }
-
     internal sealed partial class BoundParameter
     {
         public BoundParameter(SyntaxNode syntax, ParameterSymbol parameterSymbol, bool hasErrors = false)

src/Compilers/CSharp/Portable/BoundTree/NullabilityRewriter.cs

@@ -105,7 +105,7 @@ private BoundNode VisitBinaryOperatorBase(BoundBinaryOperatorBase binaryOperator
                         right,
                         type!),
                     // https://github.com/dotnet/roslyn/issues/35031: We'll need to update logical.LogicalOperator
-                    BoundUserDefinedConditionalLogicalOperator logical => logical.Update(logical.OperatorKind, logical.LogicalOperator, logical.TrueOperator, logical.FalseOperator, logical.ConstrainedToTypeOpt, logical.ResultKind, logical.OriginalUserDefinedOperatorsOpt, leftChild, right, type!),
+                    BoundUserDefinedConditionalLogicalOperator logical => logical.Update(logical.OperatorKind, logical.LogicalOperator, logical.TrueOperator, logical.FalseOperator, logical.TrueFalseOperandPlaceholder, logical.TrueFalseOperandConversion, logical.ConstrainedToTypeOpt, logical.ResultKind, logical.OriginalUserDefinedOperatorsOpt, leftChild, right, type!),
                     _ => throw ExceptionUtilities.UnexpectedValue(currentBinary.Kind),
                 };