Trax

IDE Extensions

Inlay hint extensions for VSCode and Rider/ReSharper. Both show TIn -> TOut types inline for each chain call.

What They Show

Given a train chain:

protected override async Task<Either<Exception, OrderReceipt>> RunInternal(OrderRequest input)
    => Activate(input)
        .Chain<CheckInventoryJunction>()
        .Chain<ChargePaymentJunction>()
        .Chain<CreateShipmentJunction>()
        .Resolve();

The extensions annotate each junction with its resolved types:

.Chain<CheckInventoryJunction>()      // OrderRequest -> InventoryResult
.Chain<ChargePaymentJunction>()       // InventoryResult -> PaymentConfirmation
.Chain<CreateShipmentJunction>()      // PaymentConfirmation -> OrderReceipt

Supported Methods

  • .Chain<TJunction>()
  • .ShortCircuit<TJunction>()

Type Resolution

Types are resolved by walking the junction's type hierarchy to find IJunction<TIn, TOut>. This handles:

  • Direct inheritance: class MyJunction : Junction<string, int>
  • Primary constructors: class MyJunction(ILogger logger) : EffectJunction<string, int>
  • Nested generics: EffectJunction<Unit, List<Manifest>>
  • Tuple types: EffectJunction<(List<A>, List<B>), List<C>>

VSCode

Source: plugins/vscode/trax-hints/

Installation

Install from the VSCode Marketplace

Internals

Activates on C# files. Uses regex to find chain calls, then calls VSCode's definition provider to jump to each junction's source file and extract the generic arguments from the class definition.

Resolved types are cached per junction class. The cache clears when any .cs file is modified.

Rider / ReSharper

Source: plugins/rider-resharper/

Installation

Search for Trax.Core Chain Hints in JetBrains Marketplace.

Or build from source:

cd plugins/rider-resharper
./gradlew buildPlugin

Output is in build/distributions/.

Internals

Uses JetBrains' PSI (Program Structure Interface) for type resolution. A daemon analyzer (ElementProblemAnalyzer<IInvocationExpression>) fires on each invocation expression and:

  1. Checks if the method name is Chain or ShortCircuit
  2. Extracts the type argument from the generic call
  3. Walks the junction's super-type hierarchy to find IJunction<TIn, TOut>
  4. Places a TIn -> TOut hint after the closing parenthesis

PSI resolution is fully semantic — generics, inheritance chains, and type substitution are handled correctly without regex.

Architecture

Dual-targeting project:

  • ReSharper (.NET 4.7.2): Standalone extension
  • Rider (Kotlin + .NET): .NET analysis runs in Rider's backend; Kotlin handles IDE integration

Both targets share the C# analysis code in src/dotnet/ReSharperPlugin.Trax.Core/.