Report and update deprecated APIs

When evolving an API, you have to introduce breaking changes sooner or later. The traditional way of dealing with that is to mark the deprecated types and members with the [Obsolete] attribute and explain how to migrate to the new API using the attribute's message.

ReSharper provides a more elegant solution that allows API users to find and automatically convert the old API to a new one. As the API author, you need to mark the obsolete type or member with the [CodeTemplate] attribute from JetBrains.Annotations where you can specify a search pattern to match the old API and a replacement pattern for it. The attribute will work similarly to Structural Search and Replace patterns and act as a custom code inspection with the corresponding quick-fix and fixes in scope.

[CodeTemplateAttribute] is recognized by all other JetBrains products that analyze C# code, for example, JetBrains Rider JetBrains Fleet and InspectCode Command-Line Tool.

Let's see how it works using an example:

  public class MyAssert
  {
    // Deprecated API. Usages look like:
    // MyAssert.IsTrue(args.Length > 0);
    public static void IsTrue(bool condition)
    {
      if (!condition)
        throw new Exception("Assertion failed");
    }

    // New API. Usages should look like:
    // MyAssert.That(args.Length > 0, Is.True);
    public static void That<T>(T value, Constraint<T> constraint)
    {
      // ...
    }
  }

  public class Constraint<T> { }

  class Is
  {
    public static Constraint<bool> True => null;
    public static Constraint<bool> False => null;
  }

    

Let's annotate the deprecated IsTrue() method with the [CodeTemplate] attribute:

    [CodeTemplate(
      searchTemplate: "$member$($expr$)",
      Message = "The API is deprecated, use 'MyAssert.That' instead",
      ReplaceTemplate = "MyAssert.That($expr$, Is.True)",
      ReplaceMessage = "Convert to 'MyAssert.That'")]
    public static void IsTrue(bool condition)
    {
      if (!condition)
        throw new Exception("Assertion failed");
    }

    

Now ReSharper will report all usages of MyAssert.IsTrue() and suggest a migration fix:

ReSharper: Using [CodeTemplate] attribute to suggest migration fixes for deprecated APIs

MyAssert.IsTrue(args.Length > 0);

MyAssert.That(args.Length > 0, Is.True);

Last modified: 08 April 2024