Custom Compiler Warnings


When using the ObsoleteAtribute in .Net it gives you compiler warnings telling you that the object/method/property is obsolete and somthing else should be used. I'm currently working on a project that requires a lot of refactoring an ex-employees code. I want to write a custom attribute that I can use to mark methods or properties that will generate compiler warnings that give messages that I write. Something like this

[MyAttribute("This code sux and should be looked at")]
public void DoEverything()
<MyAttribute("This code sux and should be looked at")>
Public Sub DoEverything()
End Sub

I want this to generate a compiler warning that says, "This code sux and should be looked at". I know how to create a custom attribute, the question is how do I cause it to generate compiler warnings in visual studio.

7/16/2018 3:22:51 AM

Accepted Answer


This is now possible with Roslyn (Visual Studio 2015). You can build a code analyzer to check for a custom attribute

I don't believe it's possible. ObsoleteAttribute is treated specially by the compiler and is defined in the C# standard. Why on earth is ObsoleteAttribute not acceptable? It seems to me like this is precisely the situation it was designed for, and achieves precisely what you require!

Also note that Visual Studio picks up the warnings generated by ObsoleteAttribute on the fly too, which is very useful.

Don't mean to be unhelpful, just wondering why you're not keen on using it...

Unfortunately ObsoleteAttribute is sealed (probably partly due to the special treatment) hence you can't subclass your own attribute from it.

From the C# standard:-

The attribute Obsolete is used to mark types and members of types that should no longer be used.

If a program uses a type or member that is decorated with the Obsolete attribute, the compiler issues a warning or an error. Specifically, the compiler issues a warning if no error parameter is provided, or if the error parameter is provided and has the value false. The compiler issues an error if the error parameter is specified and has the value true.

Doesn't that sum up your needs?... you're not going to do better than that I don't think.

6/23/2017 3:47:34 PM

Don't know if this will work but it's worth a try.

You can't extend Obsolete, because its final, but maybe you can create your own attribute, and mark that class as obsolete like this:

[Obsolete("Should be refactored")]
public class MustRefactor: System.Attribute{}

Then when you mark your methods with the "MustRefactor" attribute, the compile warnings might show.

I said "maybe" and "might" because I haven't tried this. Please tell me if it doesn't work so I'll remove the answer.


UPDATE: Tested it. It generates a compile time warning, but the error message looks funny, you should see it for yourself and choose. This is very close to what you wanted to achieve.

UPDATE2: With this code It generates this warnings (not very nice, but I don't think there's something better).

public class User
    private String userName;

    [TooManyArgs] // Will show warning: Try removing some arguments
    public User(String userName)
        this.userName = userName;   

    public String UserName
        get { return userName; }
    [MustRefactor] // will show warning: Refactor is needed Here
    public override string ToString()
        return "User: " + userName;
[Obsolete("Refactor is needed Here")]
public class MustRefactor : System.Attribute

[Obsolete("Try removing some arguments")]
public class TooManyArgs : System.Attribute


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