Fold F# .fsproj ordering into msbuild-antipatterns AP-05

plugins/dotnet-msbuild/skills/msbuild-antipatterns/SKILL.md

@@ -153,6 +153,8 @@ Use this catalog when scanning project files for improvements.
 
 **Exception**: Non-SDK-style (legacy) projects require explicit file includes. If migrating, see `msbuild-modernization` skill.
 
+**Exception (F# / `.fsproj`)**: F# compilation is order-dependent — the compiler processes `<Compile Include>` items sequentially and a file can only reference types/modules declared in files listed above it. `.fsproj` files must therefore list every source file explicitly, in dependency order (utility/leaf modules at the top, the entry point such as `Program.fs` at the bottom). If a `.fsi` signature file is used, it must appear **immediately before** its companion `.fs` implementation file.
+
 ---
 
 ## AP-06: Using `<Reference>` with HintPath for NuGet Packages

tests/dotnet-msbuild/msbuild-antipatterns/eval.yaml

@@ -15,3 +15,65 @@ scenarios:
       - "Identified DefineConstants overwrites existing constants instead of appending"
       - "Identified analyzer PackageReference missing PrivateAssets, unquoted MSBuild condition, mixed Include/Update in same ItemGroup, or Exec instead of Message task"
     timeout: 160
+
+  - name: "Add a module to an F# project"
+    prompt: |
+      Add a Validation.fs module to the F# project at fsharp/OrderService/ that
+      validates orders before processing. It should check that the order has at
+      least one item and that the customer name is not empty. Return a
+      Result<Order, string> with a descriptive error message on failure. Then
+      update Program.fs to validate the order before processing it, printing the
+      error if validation fails.
+    setup:
+      copy_test_files: true
+    assertions:
+      - type: "exit_success"
+      - type: "file_contains"
+        path: "fsharp/OrderService/OrderService.fsproj"
+        value: "Validation.fs"
+    rubric:
+      - "Created Validation.fs with a validation function returning Result<Order, string>"
+      - "Inserted Compile Include=\"Validation.fs\" AFTER Domain.fs and BEFORE Program.fs in the .fsproj"
+      - "Did NOT place Validation.fs after Program.fs in the Compile item list"
+      - "Updated Program.fs to call the validation function before processing"
+      - "Ran dotnet build and it succeeded"
+    timeout: 120
+
+  - name: "Fix broken file order causing FS0039"
+    prompt: |
+      The F# project at fsharp/BrokenOrder/ fails to build. Diagnose and fix the issue.
+    setup:
+      copy_test_files: true
+    assertions:
+      - type: "exit_success"
+      - type: "file_contains"
+        path: "fsharp/BrokenOrder/BrokenOrder.fsproj"
+        value: "Domain.fs"
+    rubric:
+      - "Ran dotnet build and observed FS0039 or similar 'not defined' errors"
+      - "Identified that the failure is caused by wrong file order in the .fsproj — Services.fs is listed before Domain.fs"
+      - "Reordered Compile items so Domain.fs appears before Services.fs in the .fsproj"
+      - "Did NOT modify any .fs source files to work around the ordering issue"
+      - "Ran dotnet build after the fix and confirmed it succeeds"
+    timeout: 120
+
+  - name: "Add a signature file to define public API"
+    prompt: |
+      Add a signature file (Domain.fsi) for the Domain module in the F# project at
+      fsharp/OrderService/ to explicitly define its public API surface. The
+      signature should expose all types and keep the module's public contract
+      clear. Make sure the project still builds after adding the signature file.
+    setup:
+      copy_test_files: true
+    assertions:
+      - type: "exit_success"
+      - type: "file_contains"
+        path: "fsharp/OrderService/OrderService.fsproj"
+        value: "Domain.fsi"
+    rubric:
+      - "Created Domain.fsi with type signatures matching the types in Domain.fs"
+      - "Inserted Compile Include=\"Domain.fsi\" immediately BEFORE Domain.fs in the .fsproj"
+      - "Did NOT place Domain.fsi after Domain.fs in the Compile item list"
+      - "The .fsi file contains type declarations (not implementation code)"
+      - "The project builds successfully with the signature file present"
+    timeout: 120

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/BrokenOrder/BrokenOrder.fsproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Services.fs" />
+    <Compile Include="Domain.fs" />
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+</Project>

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/BrokenOrder/Domain.fs

@@ -0,0 +1,15 @@
+module BrokenOrder.Domain
+
+type OrderId = OrderId of int
+
+type OrderItem = {
+    Name: string
+    Quantity: int
+    Price: decimal
+}
+
+type Order = {
+    Id: OrderId
+    CustomerName: string
+    Items: OrderItem list
+}

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/BrokenOrder/Program.fs

@@ -0,0 +1,14 @@
+open BrokenOrder.Domain
+open BrokenOrder.Services
+
+let order = {
+    Id = OrderId 1
+    CustomerName = "Alice"
+    Items = [
+        { Name = "Widget"; Quantity = 2; Price = 9.99m }
+        { Name = "Gadget"; Quantity = 1; Price = 24.99m }
+    ]
+}
+
+let total = processOrder order
+printfn "Order total: $%M" total

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/BrokenOrder/Services.fs

@@ -0,0 +1,12 @@
+module BrokenOrder.Services
+
+open BrokenOrder.Domain
+
+let calculateTotal (order: Order) =
+    order.Items
+    |> List.sumBy (fun item -> item.Price * decimal item.Quantity)
+
+let processOrder (order: Order) =
+    let total = calculateTotal order
+    printfn "Processing order for %s: $%M" order.CustomerName total
+    total

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/Directory.Build.props

@@ -0,0 +1,6 @@
+<Project>
+  <!-- Empty: intentionally short-circuits the parent Directory.Build.props
+       which exists only as a C# antipattern fixture and would otherwise
+       leak C#-specific settings (analyzers, TreatWarningsAsErrors) into
+       these F# fixtures. -->
+</Project>

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/Directory.Build.targets

@@ -0,0 +1,3 @@
+<Project>
+  <!-- Empty: see Directory.Build.props in this folder for rationale. -->
+</Project>

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/OrderService/Domain.fs

@@ -0,0 +1,15 @@
+module OrderService.Domain
+
+type OrderId = OrderId of int
+
+type OrderItem = {
+    Name: string
+    Quantity: int
+    Price: decimal
+}
+
+type Order = {
+    Id: OrderId
+    CustomerName: string
+    Items: OrderItem list
+}

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/OrderService/OrderService.fsproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Domain.fs" />
+    <Compile Include="Services.fs" />
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+</Project>

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/OrderService/Program.fs

@@ -0,0 +1,14 @@
+open OrderService.Domain
+open OrderService.Services
+
+let order = {
+    Id = OrderId 1
+    CustomerName = "Alice"
+    Items = [
+        { Name = "Widget"; Quantity = 2; Price = 9.99m }
+        { Name = "Gadget"; Quantity = 1; Price = 24.99m }
+    ]
+}
+
+let total = processOrder order
+printfn "Order total: $%M" total

tests/dotnet-msbuild/msbuild-antipatterns/fsharp/OrderService/Services.fs

@@ -0,0 +1,12 @@
+module OrderService.Services
+
+open OrderService.Domain
+
+let calculateTotal (order: Order) =
+    order.Items
+    |> List.sumBy (fun item -> item.Price * decimal item.Quantity)
+
+let processOrder (order: Order) =
+    let total = calculateTotal order
+    printfn "Processing order for %s: $%M" order.CustomerName total
+    total