GitHub Copilot - Generate mermaid diagrams to better understand an existing codebase

Today I was reviewing an existing codebase and I had a hard time to get a good understanding about what was going on. I couldn't create a good mental picture in my head. But then I asked myself, maybe GitHub Copilot can help me out here and draw this picture for me. Let's give it a try...

Note: As we were using the Azure DevOps wiki, I decided to try to generate the visualization using Mermaid as this is supported directly in Azure DevOps.

Let me first shortly explain what Mermaid is before I dive into Copilot.

Introduction to Mermaid

Mermaid is a powerful JavaScript-based diagramming and charting tool that allows you to create and modify diagrams dynamically. It uses Markdown-inspired text definitions to render detailed diagrams and charts, making it easy to visualize complex information. Whether you're working on flowcharts, sequence diagrams, or Gantt charts, Mermaid has you covered.

Mermaid uses a simple syntax to define charts. Here is an example of a basic flowchart:

And this is how the rendered flowchart looks like:

Creating a Mermaid chart through Copilot

Ok, time for some action. Let’s see if and how Copilot can help us to navigate through this complex codebase. Our best friend here is the @workspace command. With this command you can ask Copilot Chat questions about your entire codebase. Based on the question, Copilot intelligently retrieves relevant files and symbols, which it then references in its answer as links and code examples.

A simple example:

Let’s now combine the power of the @workspace command with Mermaid and try to construct a prompt that returns us a good mermaid diagram. Here is the prompt I tried:

@workspace Create a sequence diagram showing the data flow of the app. Please create this in mermaid format so that I can render this in a markdown file.

And this is the result I got back:

Nice!

Remark: I used the o1-preview model to generate the example above. I would recommend to certainly also try other models and compare the results.

More information

Markdown syntax for files, widgets, wikis - Azure DevOps | Microsoft Learn

Wiki Mermaid Diagrams - Azure DevOps.tips

Mermaid | Diagramming and charting tool

Chat using @workspace Context References

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME ...

Cache stampede: when our cache turned against us

While investigating some performance issues, we ran into an ASP.NET Core API that cached a fairly expensive aggregation query for 60 seconds. Under normal load, that was fine: one request rebuilds the cache, everyone else reads from it. Under peak load, dozens of requests would arrive in that same expiry window, all see a cache miss, and all fire the same expensive query in parallel. The database didn't like that. That was the moment when our caching layer stopped helping and started hurting. A burst of requests comes in at the same time, all miss the cache, and all go hammer the database or the downstream API at once. That's a cache stampede . The cache was supposed to protect our backend, and for a few hundred milliseconds it did the opposite. Why this happens IMemoryCache.GetOrCreate (and its async sibling) looks like it protects you, but it doesn't add any locking on its own. Look at the naive version: public async Task<Report> GetReportAsync(string key) ...

A complex system designed from scratch never works

A few years ago, I worked as an architect on a big mainframe rewrite. I still count it as one of my failures. Not because the technology was wrong, but because I couldn't convince the management team to simplify the approach. Years later, the organization is still struggling to get the new system up and running. I left the project at the time, because I couldn't put my name behind an approach that would take very long and cost a lot of money without a working system to show for it along the way. Gall’s Law That memory keeps coming back to me, because it's a textbook case of Gall's Law playing out in real life. Gall's Law , from John Gall's Systemantics , states it plainly: A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works, and it cannot be patched to make it work. You have to start over with a simple system that works. What does that mean in practice,...

The art of simplicity

Search This Blog