Validation

Transformers can be hard to test without a real source document, which takes time to obtain and is specific to one case. Validate() on JoltTransformer gives you a quick check of syntax and expression shapes without one.

Create the JoltJsonTransformer with the IJsonContext holding the transformer you want to check, call Validate(), and iterate over any issues it returns.

Validation doesn’t evaluate anything against a source document, so it won’t catch runtime errors such as a variable holding the wrong kind of value. It finds mistakes in how the transformer is constructed, such as syntax misuse, and it verifies that every #transformWith call resolves to a registered transformer.

Issues

Each issue is a Jolt.Structure.ValidationIssue:

public sealed class ValidationIssue
{
    public ValidationIssueType Type { get; }
    public ExceptionCode Code { get; }
    public string Message { get; }
    public string TransformerExpressionPath { get; }
    public string ExpressionText { get; }
    public bool IsInPropertyName { get; }
    public ExpressionSpan? Span { get; }
}

Property	Meaning
TransformerExpressionPath	Path to the property or array element containing the expression.
IsInPropertyName	A property’s name and value share one path, so this says whether the issue is in the name expression rather than the value.
Span	When known, the issue’s location within the expression as Start and Length.

What Span covers depends on the issue:

Issue	Span covers
Problem with a method call	The method name, e.g. #valueOf
Undeclared variable	The variable, e.g. @x
Unregistered transformer	The quoted transformer name
Syntax error	The token where parsing failed
Syntax error at the end of the expression, such as a missing )	An empty span at the end

The VS Code extension uses this same validation to show problems as you type.