Convert an Expression Tree to Source Code string

I have a function that has the following signature...

public string DoJunk(Expression<Func<bool>> expression)

I'm trying to find a way to convert the "expression" parameter back to something resembling the original source code (or at least a c# representation of the original souce code). So, if someone calls the function like this...

DoJunk(() => (i + j) * 9 == Math.Round((double)j / (i - 3), 4))

...I'd like to be able to convert the expression to this...

(i + j) * 9 == Math.Round((double)j / (i - 3), 4)

Has anyone done this?

I've just happened across this; I've written a free, open-source library which provides an extension method to create a source-code-like string from an Expression:

using AgileObjects.ReadableExpressions;

var myExpression = CreateBigExpressionTree();
var expressionSource = myExpression.ToReadableString();

I've written a blog about it, the source is on GitHub, there's a NuGet package containing the extension method, and I've written a set of Debugger Visualizers for VS 2010 -> 2019 which are in the Visual Studio Marketplace.

Here's an interesting article, with code, discussing the conversion of expression trees back into something that resembles (roughly) the original source:

Expression Trees-Lambdas to CodeDom Conversion

As a side-note, have you tried calling the expression's ToString method?

Expression<Func<int, int, bool>> expr =
    (i, j) => (i + j) * 9 == Math.Round((double)j / (i - 3), 4);

Console.WriteLine(expr.ToString());
// (i, j) => (Convert(((i + j) * 9)) = Round((Convert(j) / Convert((i - 3))), 4))

Console.WriteLine(expr.Body.ToString());
// (Convert(((i + j) * 9)) = Round((Convert(j) / Convert((i - 3))), 4))