Expression method bodies don't resolve const field references

[Jeroen-VdB]

Proposal

When a const field is referenced inside an expression method body, the toolkit emits the field reference verbatim instead of its value.

Example

Constants:

static class MyConstants { public const string Issuer = "https://my-issuer.example.com"; }

Expression:

string GetIssuer(IExpressionContext context) => context.User.Id == MyConstants.Issuer ? "yes" : "no";

Current output:

@(context.User.Id == MyConstants.Issuer ? "yes" : "no")

Expected output:

@(context.User.Id == "https://my-issuer.example.com" ? "yes" : "no")

Component

Compiler

Contact Details

jeroen@innojero.com

[AnthonyCarl]

I tried this out. It also resolves system enums to their constant value. StringComparison.OrdinalIgnoreCase turns into 5 in the C# policy expression, which results in an error in APIM.

Perhaps System.* constants should not result in the value since they are part of the runtime?

Here is test data to reproduce the error:

[DataRow(
    """
    [Document]
    public class PolicyDocument : IDocument
    {
        public void Inbound(IInboundContext context) {
            context.SetVariable("match", IsMatch(context.ExpressionContext));
        }
        bool IsMatch(IExpressionContext context)
            => string.Equals(context.Request.IpAddress, "10.0.0.1", StringComparison.OrdinalIgnoreCase);
    }
    """,
    "",
    """
    <policies>
        <inbound>
            <set-variable name="match" value="@(string.Equals(context.Request.IpAddress, "10.0.0.1", StringComparison.OrdinalIgnoreCase))" />
        </inbound>
    </policies>
    """,
    DisplayName = "Should preserve enum member access in expression body"
)]

This conditional in the ConstFoldingRewriter.cs makes the test pass (there may be a more elegant way):

var containingNamespace = field.ContainingNamespace?.ToDisplayString();
if (containingNamespace == "System" || containingNamespace?.StartsWith("System.") == true)
{
    return base.VisitMemberAccessExpression(node);
}

Happy to submit a PR if you would like.

[Mielek]

Hello @AnthonyCarl ! Thank you for trying out and finding a bug. Feel free to submit a PR for this.

Just a comment on solution. This is good workaround but I can see that in close future constant from Newtonsoft.* or Microsoft.* would be inline as well. To make sure that all cases are covered I would want this code to check if constant is define in code base or not. If it is in code base then inline. If it is not then leave as is.