How to determine if an attribute is conditionally excluded?

[erik-kallen]

It is possible to specify a [ConditionalAttribute] on an attribute type to indicate that the attribute should only be present in the compiled assembly if a certain symbol is defined when the attribute is instantiated. I need access to this information, so how can we represent it?

I suggest a bool IsConditionallyExcluded flag on IAttribute. What do you think?

[dgrunwald]

The IsConditionallyExcluded property in the type system is a good idea.

In SharpDevelop, we currently use this method in the semantic highlighter:

    bool IsInactiveConditional(IList<IAttribute> attributes)
    {
        bool hasConditionalAttribute = false;
        foreach (var attr in attributes) {
            if (attr.AttributeType.Name == "ConditionalAttribute" && attr.AttributeType.Namespace == "System.Diagnostics" && attr.PositionalArguments.Count == 1) {
                string symbol = attr.PositionalArguments[0].ConstantValue as string;
                if (symbol != null) {
                    hasConditionalAttribute = true;
                    var cu = this.resolver.RootNode as SyntaxTree;
                    if (cu != null) {
                        if (cu.ConditionalSymbols.Contains(symbol))
                            return false; // conditional is active
                    }
                }
            }
        }
        return hasConditionalAttribute;
    }

    public override void VisitAttribute(ICSharpCode.NRefactory.CSharp.Attribute attribute)
    {
        ITypeDefinition attrDef = resolver.Resolve(attribute.Type).Type.GetDefinition();
        if (attrDef != null && IsInactiveConditional(attrDef.Attributes)) {
            Colorize(attribute, inactiveCodeColor);
            return;
        }
        VisitChildren(attribute);
    }

To implement IsConditionallyExcluded, we'd just need to add a IList<string> reference to CSharpAttribute (+maybe cache the property value in CSharpResolvedAttribute).

[erik-kallen]

I don't understand 100% what you mean with the IList<string>. Do you mean that the list should contain the list of defined symbols at the point of the attribute instantiation?

[dgrunwald]

Yes, the unresolved attribute needs to store a reference to the cu.ConditionalSymbols list.

[erik-kallen]

I'm thinking about starting to implement this feature.

What do you think about also adding members called ConditionalSymbols to ITypeDefinition and IMethod, and also IsConditionallyRemoved to InvocationResolveResult?