fsharp-build-orchestration

name	fsharp-build-orchestration
description	Drive FAKE targets from the compiled front-end; golden-diff parity with DiffPlex; property/unit tests with Expecto + FsCheck.
compatibility	F# governance library (build/Governance) + build/Build.fsproj under net10.0; build-tooling scope only.
metadata	{"author":"fs-skia-ui","source":"docs/reports/2026-05-31-1714-foundations-fsharp-capabilities-and-libraries.md"}

fsharp-build-orchestration

Cookbook for the compiled build front-end, the parity gates, and the test harness. Owns C18 (build orchestration / CLI), C19 (golden-output text diffing), and C20 (property/unit testing). Verdicts come from the capability report (metadata.source) §8.

When to use

• Registering and dispatching FAKE targets from the compiled build/Build.fsproj exe (no FSX runner, no FCS).
• The Stage-4/5 golden-parity gate: prove ported output is byte-identical to the Stage-0 fixtures.
• Unit- and property-testing the ported parsers/algorithms in tests/Governance.Tests.

Library verdicts

• Orchestration / CLI (C18) → Fake.Core.Target 6.1.4 (present). The D2 spike proved it drives targets from the compiled exe with no FSX runner and no FSharp.Compiler.* transitive (FR-008). Dispatch via Target.runOrDefaultWithArguments; delegate each target body to a library function. Argu (typed CLI) and Spectre.Console (tables/colour) are optional — adopt only if the Route CLI grows.
• Golden diff (C19) → DiffPlex 1.9.0. Readable unified/side-by-side diffs for the parity gate and the Stage-2 generation-currency check. Adopt DiffPlex.
• Testing (C20) → Expecto 10.2.2 (in-tree) + FsCheck 3.3.3. Re-point moved-logic tests at the real library functions (assert typed errors, not strings). Expecto.FsCheck adds the ergonomic testProperty; until referenced, call FsCheck's Check directly inside an Expecto test.

API walkthrough + runnable examples

C18 — targets and dependency edges (Fake.Core.Target)

Target.create name body registers a target; ==> (from Fake.Core.TargetOperators) declares a dependency edge. Bodies delegate to library functions so a mistyped target/predicate fails to compile.

open Fake.Core
open Fake.Core.TargetOperators

/// C18 — register two targets and the edge Build -> Test. Dispatch (elsewhere)
/// via Target.runOrDefaultWithArguments "Test".
let defineTargets () =
    Target.create "Build" (fun _ -> ())
    Target.create "Test" (fun _ -> ())
    "Build" ==> "Test" |> ignore

C19 — golden-output parity gate (DiffPlex)

Every ported parser/algorithm/renderer must produce byte-identical output to the Stage-0 golden fixtures before the Python/Bash is deleted (Invariant 6). Return both the verdict and readable drift for the failure report.

open DiffPlex
open DiffPlex.DiffBuilder
open DiffPlex.DiffBuilder.Model

/// C19 — true when ported output equals the committed golden, with readable drift.
let goldenParity (golden: string) (ported: string) =
    let model = InlineDiffBuilder(Differ()).BuildDiffModel(golden, ported)

    let drift =
        model.Lines
        |> Seq.filter (fun line -> line.Type <> ChangeType.Unchanged)
        |> Seq.map (fun line -> sprintf "%A | %s" line.Type line.Text)
        |> Seq.toList

    List.isEmpty drift, drift

C20 — unit tests (Expecto)

open Expecto

let parserTests =
    testList "parser parity" [
        test "task id is extracted from a well-formed line" {
            let line = "- [X] T024 [skillist: []] do the thing"
            let id = line.Split(' ') |> Array.tryItem 2
            Expect.equal id (Some "T024") "the id token is the third field"
        }
    ]

C20 — property tests (FsCheck inside Expecto)

Without Expecto.FsCheck referenced, call FsCheck's Check.QuickThrowOnFailure inside a normal Expecto test — it throws on a counterexample (failing the test), exactly the gate behaviour. With Expecto.FsCheck, prefer testProperty "name" prop.

open Expecto
open FsCheck

let propertyTests =
    testList "graph properties" [
        test "reverse is an involution" {
            Check.QuickThrowOnFailure(fun (xs: int list) -> List.rev (List.rev xs) = xs)
        }
    ]

Cautions

• FAKE concurrency: never run FAKE-backed targets concurrently (shared .fake state); use the deterministic serialized order from CLAUDE.md/AGENTS.md.
• Expecto.FsCheck is a separate package — testProperty needs it; otherwise call Check directly (as above).
• Build-tooling scope. All packages are referenced by build/** or tests/Governance.Tests, never shipped in a generated product; versions go in Directory.Packages.props (Central Package Management). No FCS.
• Record warm/cold build wall-clock vs the Stage-0 baseline; the compiled library should beat the 207 KB script recompilation.

Consuming stages

Stage 5 (compiled build front-end + routing), Stage 4/5 (golden-parity exit gates), all stages (Expecto + FsCheck regression/property tests). See the plan in metadata.source.

Persistent problems

When a problem outlasts reasonable in-repo attempts, extensive external research is mandatory — consult official online docs first (the F#/.NET docs and the driven library's own documentation/API reference), then community sources (forums, Reddit, Q&A sites, issue trackers and changelogs). Record the findings and resolving links in the feature's specs/<feature>/feedback/ folder and, for durable lessons, in this skill's Sources line. Offline, the mandate degrades to recording "research blocked — " rather than hard-failing the phase.

Sources / links

• Fake.Core.Target: https://fake.build/reference/fake-core-target.html
• DiffPlex: https://github.com/mmanela/diffplex
• Expecto: https://github.com/haf/expecto · FsCheck 3: https://fscheck.github.io/FsCheck/
• Capability report: docs/reports/2026-05-31-1714-foundations-fsharp-capabilities-and-libraries.md §8.

Related

[[fsharp-parsing]], [[fsharp-graph-algorithms]] (the ported logic under test), [[fsharp-code-generation]] (DiffPlex also backs the currency check), [[fsharp-io-globbing]], [[fsharp-shell-process]] (the residual processes the front-end drives).