F# codegen: FluentValidation + CosmosDB slice — runnable sample + compile-gate (GH-2969)

[jeremydmiller]

Part of the F# code-generation audit (#2969). A combined F# sample exercising two middleware surfaces in one handler — FluentValidation + CosmosDB persistence — plus a compile-gate proving the chain emits valid F#.

Frame F# emit

Only one frame needed new F# emit:

• CosmosDB TransactionalFrame → context.EnlistInOutbox(CosmosDbEnvelopeTransaction(container, context)) (EnlistInOutbox is synchronous; CosmosDbEnvelopeTransaction is already public).

Everything else was already F# via MethodCall/existing frames:

• FluentValidation → do! FluentValidationExecutor.ExecuteOne<T>(validator, failureAction, msg).
• ISideEffect (the returned ICosmosDbOp) → if not (isNull outgoing1) then do! outgoing1.Execute(container).
• Outbox flush → do! context.FlushOutgoingMessagesAsync().

Generated F# (from the gate):

task {
    let createThingValidator = WolverineCosmosFSharpSample.CreateThingValidator()
    let createThing = context.Envelope.Message :?> WolverineCosmosFSharpSample.CreateThing
    do! Wolverine.FluentValidation.Internals.FluentValidationExecutor.ExecuteOne<...CreateThing>(createThingValidator, _failureActionOfCreateThing, createThing)
    // Enlist in CosmosDB outbox transaction
    context.EnlistInOutbox(Wolverine.CosmosDb.Internals.CosmosDbEnvelopeTransaction(_container, context))
    let outgoing1 = WolverineCosmosFSharpSample.CreateThingHandler.Handle(createThing)
    if not (isNull outgoing1) then
        do! outgoing1.Execute(_container)
    do! context.FlushOutgoingMessagesAsync()
}

Runnable sample — src/Samples/WolverineCosmosFSharpSample

F# CreateThing command + CreateThingValidator : AbstractValidator<CreateThing> + a [<Transactional>] CreateThingHandler returning CosmosDbOps.Store(thing). UseFluentValidation() + UseCosmosDbPersistence(db). Runs via dynamic codegen (Wolverine.RuntimeCompilation + opts.UseRuntimeCompilation(), #2876) against the Cosmos emulator (the sample pre-creates the database, since Wolverine's resource setup only creates containers). Verified end-to-end: prints Stored a Thing through the F# Wolverine + CosmosDB handler (with FluentValidation).

F# + FluentValidation note

AbstractValidator<T>.RuleFor takes a LINQ Expression<Func<T,TProperty>>; F# auto-converts the property-selector lambdas (fun x -> x.Name) to expression trees, so the validator reads naturally.

Compile-gate — src/Testing/Wolverine.Cosmos.FSharp{Tests,Fixture}

Renders the sample's real CreateThing chain to F# via the no-host HandlerGraph → AssembleTypes → GenerateFSharpCode path, then dotnet builds the fixture. No live Cosmos connection (the CosmosClient is constructed lazily and never used at codegen).

Wire-up

• Sample + gate added to wolverine_fsharp.slnx.
• fsharp.yml runs the FluentValidation + CosmosDB gate as its own sequential step.

Verification

• Compile-gate green.
• dotnet build wolverine.slnx -c Release clean (per CLAUDE.md the slim build isn't sufficient).
• Sample runs end-to-end against the Cosmos emulator.

🤖 Generated with Claude Code