feat(fsharp): m01-m06 util, model, rules, random, spawn, game, view with Expecto tests

Co-Authored-By: Claude Opus 5.5 <[email protected]>

fsharp/tests/Purity.fs

@@ -0,0 +1,54 @@
+module Snake.Tests.Purity
+
+open System.IO
+open System.Text.RegularExpressions
+open Expecto
+
+let private srcDir = Path.Combine(Directory.GetCurrentDirectory(), "src")
+
+// The one file allowed to touch the outside world (the browser glue lives in web/, outside src/).
+let private excluded (file: string) = Path.GetFileName(file) = "Runtime.fs"
+
+let private banned: (string * Regex * string) list =
+    [ "mutable", Regex(@"\bmutable\b"), "let mutable n = 0"
+      "<-", Regex(@"<-"), "n <- n + 1"
+      "System.Random", Regex(@"\bSystem\.Random\b"), "let r = System.Random()"
+      "DateTime", Regex(@"\bDateTime\b"), "let t = System.DateTime.Now"
+      "printf", Regex(@"\bprintf"), "printfn \"hi\""
+      "ref ", Regex(@"\bref "), "let cell = ref 0" ]
+
+// Block comments `(* ... *)` and line comments (`//`, `///`) are removed before scanning.
+let private stripComments (code: string) =
+    Regex.Replace(Regex.Replace(code, @"(?s)\(\*.*?\*\)", ""), @"(?m)//.*$", "")
+
+let private violations (code: string) =
+    let clean = stripComments code
+    [ for name, re, _ in banned do
+          if re.IsMatch clean then
+              yield name ]
+
+let private fsFiles () =
+    if Directory.Exists srcDir then
+        Directory.GetFiles(srcDir, "*.fs", SearchOption.AllDirectories) |> Array.sort |> List.ofArray
+    else
+        []
+
+[<Tests>]
+let tests =
+    testList "Purity" [
+        for name, _, sample in banned do
+            yield testCase $"purity scanner flags a known-bad sample using {name}" (fun () ->
+                Expect.contains (violations sample) name "flagged")
+
+        yield testCase "purity scanner ignores banned words inside comments" (fun () ->
+            let code = "// let mutable x\n(* x <- 1; printfn \"hi\" *)\nlet a = 1 // System.Random DateTime ref x\n"
+            Expect.equal (violations code) [] "no violations")
+
+        yield testCase "purity scanner accepts ordinary pure code" (fun () ->
+            Expect.equal (violations "let f xs = List.map (fun x -> x + 1) xs") [] "no violations")
+
+        for f in fsFiles () do
+            if not (excluded f) then
+                yield testCase $"purity: {Path.GetRelativePath(srcDir, f)} has no banned constructs" (fun () ->
+                    Expect.equal (violations (File.ReadAllText f)) [] "violations")
+    ]