The Roslyn project is the next generation of C# and VB compilers but paradoxically it is not interesting because of the new features that will come into the next versions of the languages. Microsoft opened the compiler APIs publicly allowing the developers to create programs and tools which takes advantage of the syntactic and semantical analysis of the code. During the session we will see how the developer can use the compiler APIs to format the sources, compile or understand the code even when it still contains errors. One of the most interesting uses of these APIs is the creation of semantic rules to enforce at compile time like, for example, guidelines or even static business rules.

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Look at your code from a
different perspective
twitter: @raffaeler
email: raffaeler@vevy.com
blog: http://www.iamraf.net
The Roslyn compiler:

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Huge thanks to our sponsors & partners!

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• .NET C# and VB compilers totally re-written
–Using C# and VB
• Open source under the Apache 2.0 license
–https://roslyn.codeplex.com/
• Will be shipped with VS.NET vNext
Roslyn aka ".NET Compiler Platform"
git repo
Usually a new
compiler is important
because of new
language features …

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1. Auto-properties initializers
2. Primary constructors
3. Using static
4. Declaration Expressions
Upcoming C#6.0 new features
public string Name { get; set; } = “Raf”;
public class Dog(string name) {
public string Name { get; } = name;
}
using System.Console;
using System.Math;
if(double.TryParse(text, out double value)) { … }
WriteLine("Hello, world {0}", Max(a, b));
ReadKey();

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5. Exception filters
6. Binary literals and digit separators
7. Indexed members and element initializers
8. Await in catch and finally blocks
Upcoming C# 6.0 new features
var bits1 = 0b00010001;
var bits2 = 0b0001_0001;
var hex = 0x00_C6;
var dec = 1_234_000;
try { … }
catch(SomeException e) if(myFilter(e)) { … }
customer["first“] = “Raf“; customer.$first = “Raf“;
catch(…) { await … }
finally { await … }

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Why Roslyn is relevant?
• Microsoft perspective
– Only one compiler engine for both VB and C#
– Future evolutions of C# and VB will be easier to
implement
– Better tooling inside Visual Studio
• Visual Studio plugin developers
– Better refactoring, coloring, helpers, static analysis, etc.
• All the other developers
– Using C# and VB as scripting languages
– Documentation and code-search via syntactical analysis
– Enforcing business rules with custom semantical
analysis

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Where to start
I want to just try the new compiler
– Nuget package: Microsoft.Net.ToolsetCompilers
– Will use the compiler inside the package itself
Tools for developers
– Nuget package:
Microsoft.CodeAnalysis.CSharp.Workspaces
Solutions using Compilers and tools
– Nuget package:
Microsoft.CodeAnalysis (contains all)
Visual Studio templates

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THE PIPELINE

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The pipeline workflow
• The source is tokenized
– Syntax analysis using the grammar rules
• Recognizing the declarations
– Symbols creation to name variables, classes, methods, …
• Binding the identifiers with symbols
– Retrieve symbolic information from nodes
• The code is generated to form the assembly
– Generation of the PE file, manifest, IL code, resources, etc.
– Note: the APIs for reading/writing these files is marked 'internal'
Parsing
sources
Creating
symbols
Semantic
model
IL Emitter

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• Transformation from text to nodes is reversible
– Full fidelity (comments and alignments as well)
• Every syntax tree is immutable and thread-safe
– Allow multiple consumers to access concurrently
a single tree
Parsing the sources
… ……

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• Syntax API is represented with these classes:
– SyntaxTree is the binary form of the source with full
fidelity
– SyntaxNode represents declarations, statements,
clauses and expressions
– SyntaxToken identifies the special language tokens like
keywords, identifiers, operators or punctuation
• They never have children
– SyntaxTrivia everything not impacting on the generated
IL code such as whitespaces, comments, etc.
From sources to syntax tree
SyntaxTree tree = CSharpSyntaxTree.ParseText(source);
SyntaxNode node = tree.GetRoot();
Debug.Assert(node.CSharpKind() == SyntaxKind.CompilationUnit);
var root = (CompilationUnitSyntax)node;

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Visual Studio Syntax Tree tool

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Applying the language rules
• The syntax tree represent only the basic info
• The compilation applies the language rules to
the syntax tree and extracts the symbols
– Symbols are declared namespaces, types,
members, variables, etc.
• Compilations are immutable too
– therefore they are thread-safe
SyntaxTree tree = CSharpSyntaxTree.ParseText(source);
var compilation = CSharpCompilation.Create("CSharpColorizer",
new SyntaxTree[] { tree },
_metadataFileReferences,
new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
var result = compilation.Emit(ms); // optional

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Semantics
• «Semantics is the study of the meaning»
– This translates in "understanding the code"
• Semantic info correlates the symbols derived
from the syntax tree and accessing:
– The exact location in the sources
– Warnings and errors
– The types returned from an expression
– Much more!
• SemanticModel is immutable and thread-safe

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Working with projects and solutions
• Symbolic dependencies may affect even an
entire VS Solution
–The compiler needs to know about solutions,
projects, files
• Workspace API entry-points
–Workspaces resemble solutions
–Projects are, well, projects
–Documents are the files subject to compilation

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Workspaces
var workspace = new CustomWorkspace();
var solution = workspace.CurrentSolution; // the only solution
var project = solution.AddProject(
"projectName", "assemblyName", LanguageNames.CSharp);
var mainDocument = project.AddDocument("fake.cs", source);
• Workspaces fire events
– On opening/closing documents
– When something change in the solution
– If an error occurs
• Flowchart:
– IDE opens & closes the documents, refactors the code, …
– Tools receive the events and reacts appropriately
• CustomWorkspace allows working on the fly (no IDE)
Workspace
(Solution)
Project
Document

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Model hierarchy
Host (IDE)
Workspace
Solution v1
Project1 Project2 Project3
Document1 Document2
Text Syntax SemanticModel
Tools
Solution v2

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• Roslyn compiler is deterministic
–Same sources  identical binary
–Super-important for debugging!
• Immutable and thread-safe APIs
–Syntax trees, Compilation, SemanticModel,
Solution, Project, Document
• http://referencesource.microsoft.com/
–Roslyn powered
Tips

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Questions?