In the previous article we looked at the result of parsing stage of compilation - syntax graph, how it represent information available to C# compiler from analyzing a single file of code and, consequentially, reflects that text quite faithfully and how to transform it to refactor existing code. In this article we will look at symbol graph - result of the next stage of compilation - binding.
In the syntax graph you can see that core C# concepts are represented by corresponding node type, like ClassDeclaration or MethodDeclaration. Inside they often contain IdentifierTokens representing the textual name of some type, but that is as much information as you initially get. In order to get information about a particular type, like its namespace or members, you’d need to get its symbol by performing a costly binding process – check which namespaces are currently used in the file, look for type declarations through the entire solution and all imported DLLs that match, compile them if need be, etc. - compile everything.
The symbol graph allows you to answer a lot more meaningful questions than syntax graph. Want to track down all usages of a specific type? Rename something solution-wide? You can do that.
You can trigger a limited binding for a given piece of syntax graph, or you can hook into the compilation process of the IDE itself (it is continuously recompiling your solution on every change to warn you of any errors as you type away). This common way to do this is by creating a class inheriting from DiagnosticAnalyzer.
From the point of view of developer using it (we will call them 'user-dev'), Refactorings in Roslyn are additional commands that pop-up in Visual Studio when they click certain pieces of code. From our point of view, Refactorings are classes inheriting from CodeRefactoringProvider, which get a chance to examine current syntax graph every time user-dev clicks something in it and determine, if they should offer any transformations of that graph based on its state and what was clicked.
We will be building a Refactoring which allows our user-dev to regenerate a given classes public constructor by adding to it any missing assignment of members that match a certain pattern and are not yet assigned during construction. Specifically, this is the refactoring we use at work to regenerate dependency injected constructors.
.NET Compiler Platform, better known as Roslyn, has been one of the best things that happened to C#. In short, it is a compiler made with IDE integration and extensibility in mind. It provides us with hooks to add our own analysis and transformations to the process of compilation. Why is that important? If there was ever a coding rule specific to just one of your projects, that you had to inforce with lots of discipline and diligence, but would rather rely on the compiler for it, or a routine operation you could easily automate if only you could write an IDE extension – Roslyn will make this a reality. It allows you to write code, C# code in my case, that will run as a Visual Studio extension, analyze the code other devs are working on and help them modify it.
Unfortunately, despite initially releasing with Visual Studio 2015, there is still lack of tutorials teaching how to do things beyond ‘Hello world’. For serious development, the best way to learn is to read official documentation wiki and study other prjects available on github - quite a lot of overhead, even if Roslyn is worth it. This series will provide with a more streamlined roadmap - enough knowledge to do useful things and guidelines for farther research. Through the series we will build a refactoring extension for Visual Studio and a simplistic analyzer dll to include into a project. Both small enough to comprehend in an hour, yet performing useful work, solving a task the likes of which you may expect to want to automate yourself in your project. As well as techncial infromation, which can be quite overwhelming at first site, I will try to give hints on the general flow of Rolsyn development: how to decide where to start, how to deal with roadblocks, how to concentrate on important things first.