Okey, I find the way by myself! Here is the CodeFix:
if (node.IsKind(SyntaxKind.SimpleAssignmentExpression))
{
var IncrementationClause = (BinaryExpressionSyntax)node;
var IncrementionClauseExpressionStatement = IncrementationClause.Parent;
string right = IncrementationClause.Right.ToString();
string left = IncrementationClause.Left.ToString();
var ExpressionNew = SyntaxFactory.ExpressionStatement(IncrementationClause);
if (right == left + " - 1")
{
var BonneIncrementation = SyntaxFactory.PostfixUnaryExpression(SyntaxKind.PostDecrementExpression, IncrementationClause.Left);
ExpressionNew = SyntaxFactory.ExpressionStatement(BonneIncrementation).WithAdditionalAnnotations(Formatter.Annotation).WithLeadingTrivia(leading).WithTrailingTrivia(trailing);
}
else
{
var BonneIncrementation = SyntaxFactory.PostfixUnaryExpression(SyntaxKind.PostIncrementExpression, IncrementationClause.Left);
ExpressionNew = SyntaxFactory.ExpressionStatement(BonneIncrementation).WithAdditionalAnnotations(Formatter.Annotation).WithLeadingTrivia(leading).WithTrailingTrivia(trailing);
}
var newRoot = root.ReplaceNode(IncrementionClauseExpressionStatement, ExpressionNew);
return new[] { CodeAction.Create("Convert in the good way of incrementing", document.WithSyntaxRoot(newRoot)) };
}