Fix #1147: Use C# 7.3 syntax for ref reassignment.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -500,7 +500,17 @@ namespace ICSharpCode.Decompiler.CSharp
 					inst.Variable.Type = type;
 				}
 			}
-			return Assignment(ConvertVariable(inst.Variable).WithoutILInstruction(), translatedValue).WithILInstruction(inst);
+			var lhs = ConvertVariable(inst.Variable).WithoutILInstruction();
+			if (lhs.Expression is DirectionExpression dirExpr && lhs.ResolveResult is ByReferenceResolveResult lhsRefRR) {
+				// ref (re-)assignment, emit "ref (a = ref b)".
+				lhs = lhs.UnwrapChild(dirExpr.Expression);
+				var assign = new AssignmentExpression(lhs.Expression, translatedValue.Expression)
+					.WithRR(new OperatorResolveResult(lhs.Type, ExpressionType.Assign, lhsRefRR, translatedValue.ResolveResult));
+				return new DirectionExpression(FieldDirection.Ref, assign)
+					.WithoutILInstruction().WithRR(lhsRefRR);
+			} else {
+				return Assignment(lhs, translatedValue).WithILInstruction(inst);
+			}
 
 			bool IsOtherValueType(IType type)
 			{

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -65,7 +65,17 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			return new ExpressionStatement(exprBuilder.Translate(inst));
 		}
-		
+
+		protected internal override Statement VisitStLoc(StLoc inst)
+		{
+			var expr = exprBuilder.Translate(inst);
+			// strip top-level ref on ref re-assignment
+			if (expr.Expression is DirectionExpression dirExpr) {
+				expr = expr.UnwrapChild(dirExpr.Expression);
+			}
+			return new ExpressionStatement(expr);
+		}
+
 		protected internal override Statement VisitNop(Nop inst)
 		{
 			var stmt = new EmptyStatement();

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -386,14 +386,16 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 
 		bool IsMatchingAssignment(VariableToDeclare v, out AssignmentExpression assignment)
 		{
-			assignment = v.InsertionPoint.nextNode as AssignmentExpression ?? (v.InsertionPoint.nextNode as ExpressionStatement)?.Expression as AssignmentExpression;
-			Expression expectedExpr = new IdentifierExpression(v.Name);
-			if (v.Type.Kind == TypeKind.ByReference) {
-				expectedExpr = new DirectionExpression(FieldDirection.Ref, expectedExpr);
+			assignment = v.InsertionPoint.nextNode as AssignmentExpression;
+			if (assignment == null) {
+				assignment = (v.InsertionPoint.nextNode as ExpressionStatement)?.Expression as AssignmentExpression;
+				if (assignment == null)
+					return false;
 			}
-			if (assignment != null && assignment.Operator == AssignmentOperatorType.Assign && assignment.Left.IsMatch(expectedExpr))
-				return true;
-			return false;
+			return assignment.Operator == AssignmentOperatorType.Assign
+				&& assignment.Left is IdentifierExpression identExpr
+				&& identExpr.Identifier == v.Name
+				&& identExpr.TypeArguments.Count == 0;
 		}
 
 		void InsertVariableDeclarations(TransformContext context)