A new look for .NET Reference Source

A new look for .NET Reference Source

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This post was written by Alok Shriram, Program Manager on the .NET Framework team. He will show you a significantly improved experience around .NET Reference Source.

Today I'm very excited to announce that we have an awesome new experience to use the .NET Framework reference source.

Browsing .NET Reference Source

First of all, most people just want to look at code. So we've added a brand new source browsing experience. For a tutorial, checkout our Channel 9 video:

This new browsing experience provides the following features:

  • Go to Definition and Finding References. You can now browse through .NET framework code in a Visual Studio like experience with features analogous to “Go to Definition” and “Find All References”. This tool was developed for internal use but we found it to be so incredibly useful that we had to share it with you. The video above highlights some of the cool features of this site and how you can use it. For more details, checkout the help page.

  • Offline Browsing. You can download the entire reference source as a zip file, which now also includes project and solution files, so that you can easily open and browse it in VS.

  • Jump to Reference Source right from Visual Studio. Schabse Laks has written an extension to VS called Ref12. This extension changes the behavior of F12 to jump to the online browser for symbols that aren’t in your solution but are part of the .NET Reference Source. If you have any more interesting ideas around how you can use leverage this site please touch base with us by using the feedback button on the site or leave a comment here in the post.

We generated this site using Project Roslyn, our new C# and VB compilers.

Using .NET Reference Source for debugging

We are also happy to announce that you can now step through .NET framework sources for .NET framework 4.5.1 and any associated patches and updates.

This has been one of the highest voted items on User Voice:

We are pleased to close this item as resolved. To read about how to setup VS to take advantage of this feature please go here.

So what does it mean for your day-to-day activities? Let’s assume that you have an app that uses List<string> to display a set of controls. One day after a framework update you suddenly realize that the order of the controls in your app has suddenly changed. You fire up VS and follow the instructions described above and start stepping through you code like you normally would. You get to the point where you were doing your sorting:

Hit F11 and voila you are in the List<T>.Sort code! Sweet.

We find that this is an extremely useful diagnostic tool for our developers when they are investigating issues internally. So we decided to fix this experience so that it also "just works" for you. This will give you the ability to better understand and diagnose issues between our and your code.

Improvements when debugging .NET Reference Source

Historically since the inception of this effort, we have published sources and PDBs for every major .NET framework update namely .NET framework 4.0 and 4.5. However these builds would be rendered effectively useless the moment any update to the framework was released, since the binaries on the updated box no longer matched the PDBs that were indexed on the reference source server. Unfortunately the design of the system that we had in place was geared towards doing single and infrequent pushes of sources and symbols out and did not account for the sheer volume of builds and patches that come are produced out of the .NET framework build system.

Starting with .NET 4.5.1 we have radically changed the symbol indexing and publishing process to be in sync with the build process such that as and when updates are shipped , the corresponding PDBs are also updated to the reference source site appropriately. The summary of this is going forward the reference source debugging experience should just work. If it does not use the troubleshooting instructions at the link provided above and send us an email with the data requested, we will do our best to turn it around quickly.

There is one caveat to this experiences; for security updates or updates that are otherwise deemed to have changes that we do not want leaked (think security exploits) you will still have a debugging experience, but rather than the file that corresponds to that PDB, you will get the last broadly shipped copy of that file. This could manifest itself in a slightly skewed debugging experience if you are stepping through a file where the fix was made.

How does reference source relate to the Microsoft Symbol Server?

The Microsoft Symbol Server is a repository where all public PDBs generated by most teams at Microsoft end up. However all PDBs that are present here do not have any source information in them, which makes them not very useful for stepping through sources. When you are trying to debug .NET Framework source please ensure that you do not have the Microsoft Symbol Server enabled. Doing so could result in the symbols being loaded from the Microsoft Symbol Server and the source stepping experience would not work in that case. You can disable Microsoft Symbol Server lookup via Tools | Options | Debugging | Symbols. Ensure that the checkbox in front of Microsoft Symbol Server is unchecked.

What's next?

But wait! There is more:

  • Replacing referencesource.microsoft.com. Our most immediate goal is to retire the current page at http://referencesource.microsoft.com in favor of the new browsing experience. Please take a look at the old site and let us know of any concerns you have around deprecating it.

  • Updating the indexed sources. The version of the framework that we currently have indexed is .NET Framework 4.5.1. Due to the improvements we made in our engineering system, we're now able to update both the symbols and the sources as new versions of the framework are released.

  • Adding source for assemblies. As you can probably notice, the set of assemblies that we have is not complete. We don't intend to keep it that way, so we plan to expand the set of assemblies over time.


Today we announced a new browsing experience for the .NET Reference Source. We've also fixed the long standing issue with using reference source for debugging.

We would love to hear your feedback. Please let us know what you think about the new browsing experience by leaving a comment on this blog or by emailing us. Also, if you're missing specific assemblies, please let us know so that we can prioritize which ones we add first.

Happy browsing & debugging!

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  • LMK: No this does not include the exact source that shipped in WP8. However, WP8 and .NET Framework build from the same sources, so while you cannot step into WP8, you can browse the source and have a fairly good indication of what shipped in WP8.

    David Kean

  • Guys please consider implementing single instruction multiple data (SIMD) support in C#.NET.

    Its being a LONG time, mono is teasing .NET.

    Will it ever happen? Clues !?!?

  • I do not see exactly how this is related to Roslyn, could you say more about that? Thanks!

  • @Jackie boy: Usual disclaimer that I can't commit on anything but we are taking a serious look at SIMD.

    @Pierre: Sure. Our awesome friend and MVP Schabse Laks has written a great blog post about how Roslyn powers .NET Reference Source. blog.slaks.net/.../dissecting-the-new-net-reference-source-browser

  • Thanks! that's good!!

  • I wasn't a big fan of the current reference source.

    Firstly, the names of the files on referencesource.microsoft.com that you could download were non-sensical. You couldn't easily tell which .NET version each file was for.

    Secondly, the actual code was a mess:

    A) Files had inconsistent formatting among them.

    B) Code formatting was awful. Some lines had spaces at the end, other times there were unnecessary imports and other times multiple unnecessary blank lines, while the comments were full of spelling mistakes, wrong punctuation and were not really clear. Lines were too long and methods were randomly scattered around the file. It seemed that Microsoft had no consistent formatting rules that all developers were forced to follow.

    C) The actual code was awful. Wrongly designed class hierarchies and poorly written code that did not seem to care about error conditions, especially for WPF. Compared to other projects for which I have seen the code it was really bad. For example, Google's Closure library is very well written, with excellent comments and algorithm implementations which seem to be robust against all conditions.

    D) There were no unit tests and the code did not appear to have been written with testability in mind, so I doubt that the unit tests were simply omitted.

    I seriously hope that you have improved all the above shortcomings.

  • Plus, I forgot to say that, each file had the same code written twice in it and the folder structure was non-sensical.

  • Audio on the video would have been fantastic ... just saying

  • Really nice tool, I've already used it several times. It took me a while to realize I can click on almost anything... great.

    Is it possible to add the version to the URL? I'm a little worried when I use a link like  /#mscorlib/system/gc.cs#17 , because one day the file will be updated, and the line numbers will change (or the file will be renamed)...

  • Is there *anyone* outside Microsoft who has got it to work yet?

    Just like adigostin wrote, it does not work for me either. I tried a minimal List<> example, using VS 2013 Professional and .NET 4.5.1.

    I wonder if it is really enough to unselect "Microsoft Source Server" and not adding any replacement URL or path?

  • And please add System.Windows.Forms.DataVisualization.dll


  • @Nick I hope you have found the new experience to be a more pleasant one.  With regards to things like code quality, please let us know in case things are busted or broken using the feedback links on the site and we will definitely take a look. We are already aware of some files having some artifacts due to a bug in our sanitization process.

    @Jon Preece We got that feedback :) sorry for the silent movie.  Will work on updating the video with a music track at least.

    @Bernhard please send us the information that we requested on the troubleshooting site.  We realized in our attempt to reindex all the builds, one build got missed the file version on the DLL is 30319.34004.  We are going to add that in soon.   and noted w.r.t System.Windows.Forms.DataVisualization.dll

  • I have been wanting this for a very long time.

  • Are you excluding the security patches just in case the black hats haven't discovered Reflector yet?

    That's a joke, right?

  • I got it to work within VS 2013 with a little help from Alok. The key step that I was missing was to clear the symbol cache from previously loaded PDBs without source references, using Tools|Options|Debugging|Symbols|Empty Symbol Cache.

    Many thanks, this is very useful.

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