Run the test after mutating

.editorconfig

@@ -0,0 +1,14 @@
+root = true
+
+[*]
+indent_style = space
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.nix]
+indent_size = 2
+
+[*.{fs,fsi,fsx}]
+indent_size = 4

Example.Tests/CalculatorTests.fs

@@ -6,17 +6,22 @@ open Xunit
 
 type CalculatorTests() =
     [<Fact>]
-    [<MutationCase("calc-add-one", "Example.Tests/Calculator.fs", 4, "value + 1", "value - 1")>]
-    member _.AddOne_increments() =
-        Assert.Equal(42, Calculator.addOne 41)
+    [<MutationCase("""
+    diff --git a/Example.Tests/Calculator.fs b/Example.Tests/Calculator.fs
+    index cfcce3b..39be7f3 100644
+    --- a/Example.Tests/Calculator.fs
+    +++ b/Example.Tests/Calculator.fs
+    @@ -1,7 +1,7 @@
+     namespace Example
 
-    [<Fact>]
-    [<MutationCase("calc-abs-diff-branch", "Example.Tests/Calculator.fs", 7, "left - right", "right - left")>]
-    member _.AbsoluteDifference_preserves_order() =
-        Assert.Equal(7, Calculator.absoluteDifference 10 3)
+     module Calculator =
+    -    let addOne value = value + 1
+    +    let addOne value = value - 1
 
-    [<Fact>]
-    [<MutationCase("calc-leap-year-century", "Example.Tests/Calculator.fs", 10, "year % 100 <> 0", "year % 100 = 0")>]
-    member _.LeapYear_handles_centuries() =
-        Assert.True(Calculator.isLeapYear 2000)
-        Assert.False(Calculator.isLeapYear 1900)
+         let absoluteDifference left right =
+             if left >= right then left - right else right - left
+
+        member _.AddOne_increments() =
+            Assert.Equal(42, Calculator.addOne 41)
+    """)>]
+    member _.AddOne_increments() = Assert.Equal(42, Calculator.addOne 41)

Example.Tests/MutationCaseAttribute.fs

@@ -3,11 +3,7 @@ namespace Mutannot
 open System
 
 [<AttributeUsage(AttributeTargets.Method, AllowMultiple = true)>]
-type MutationCaseAttribute(id: string, file: string, line: int, find: string, replace: string) =
+type MutationCaseAttribute(patch: string) =
     inherit Attribute()
 
-    member _.Id = id
-    member _.File = file
-    member _.Line = line
-    member _.Find = find
-    member _.Replace = replace
+    member _.Patch = patch

Mutannot/Program.fs

@@ -1,7 +1,12 @@
+open System
+open System.IO
+open System.Reflection
+open System.Runtime.InteropServices
 open Fli
 
-[<EntryPoint>]
-let main argv =
+type MutationCase = { TestName: string; Patch: string }
+
+let ensureCleanWorkingDirectory () =
     let gitState =
         cli {
             Exec "git"
@@ -12,6 +17,123 @@ let main argv =
 
     if gitState.Text <> None then
         eprintfn "Uncommitted changes. Refusing to run."
+        exit 2
+
+let applyPatch patch =
+    cli {
+        Exec "git"
+        Arguments [ "apply"; "-" ]
+        Input patch
+    }
+    |> Command.execute
+    |> Output.throwIfErrored
+    |> ignore
+
+let restore () =
+    cli {
+        Exec "git"
+        Arguments [ "restore"; "--staged"; "--worktree"; "." ]
+    }
+    |> Command.execute
+    |> Output.throwIfErrored
+    |> ignore
+
+let ensureBuilt projectPath =
+    cli {
+        Exec "dotnet"
+        Arguments [ "build"; projectPath ]
+        Output(new StreamWriter(Console.OpenStandardOutput()))
+    }
+    |> Command.execute
+    |> Output.throwIfErrored
+    |> ignore
+
+let runTest projectPath testName =
+    cli {
+        Exec "dotnet"
+        Arguments [ "test"; projectPath; "--filter"; $"FullyQualifiedName={testName}" ]
+        Output(new StreamWriter(Console.OpenStandardOutput()))
+    }
+    |> Command.execute
+    |> ignore
+
+let getAssemblyPath projectPath =
+    cli {
+        Exec "dotnet"
+        Arguments [ "msbuild"; projectPath; "--getProperty:TargetPath" ]
+    }
+    |> Command.execute
+    |> Output.toText
+
+let getMetadataLoadContext (assemblyPath: string) =
+    // This allows us to inspect assemblies regardless of the platform that they were built for
+    // https://learn.microsoft.com/en-us/dotnet/standard/assembly/inspect-contents-using-metadataloadcontext
+    let assemblyDir = Path.GetDirectoryName assemblyPath
+
+    let pathAssemblyResolver =
+        [ yield assemblyPath
+          yield! Directory.EnumerateFiles(assemblyDir, "*.dll")
+          yield! Directory.EnumerateFiles(assemblyDir, "*.exe")
+          yield! Directory.GetFiles(RuntimeEnvironment.GetRuntimeDirectory(), "*.dll") ]
+        |> PathAssemblyResolver
+
+    new MetadataLoadContext(pathAssemblyResolver, typeof<obj>.Assembly.GetName().Name)
+
+let unindented (s: string) =
+    let lines = s.Split([| "\r\n"; "\n" |], StringSplitOptions.None)
+
+    let indexOfFirstNonEmptyLine =
+        lines |> Array.findIndex (not << String.IsNullOrWhiteSpace)
+
+    let identantionOfFirstNonEmptyLine =
+        lines[indexOfFirstNonEmptyLine] |> Seq.takeWhile Char.IsWhiteSpace |> Seq.length
+
+    lines[indexOfFirstNonEmptyLine..]
+    |> Seq.map (fun line -> line.Substring(min identantionOfFirstNonEmptyLine line.Length))
+    |> String.concat Environment.NewLine
+
+let getMutationCases projectPath =
+    ensureBuilt projectPath
+
+    let assemblyPath = getAssemblyPath projectPath
+
+    use metadataLoadContext = getMetadataLoadContext assemblyPath
+
+    let assemblyTypes =
+        assemblyPath |> metadataLoadContext.LoadFromAssemblyPath |> _.GetTypes()
+
+    let assemblyMethods =
+        assemblyTypes
+        |> Seq.collect _.GetMethods(BindingFlags.Public ||| BindingFlags.Instance)
+
+    assemblyMethods
+    |> Seq.collect (fun m ->
+        m.GetCustomAttributesData()
+        |> Seq.choose (fun attr ->
+            match attr.AttributeType.FullName with
+            | "Mutannot.MutationCaseAttribute" ->
+                Some
+                    { TestName = $"{m.DeclaringType.FullName}.{m.Name}"
+                      Patch = attr.ConstructorArguments[0].Value :?> string |> unindented }
+            | _ -> None))
+    |> Seq.toList
+
+[<EntryPoint>]
+let main argv =
+    if argv.Length <> 1 then
+        eprintfn "Usage: mutannot <path/to/project.csproj|fsproj>"
         exit 1
 
+    ensureCleanWorkingDirectory ()
+
+    AppDomain.CurrentDomain.ProcessExit.Add(fun _ -> restore ())
+
+    let projectPath = argv[0]
+
+    for mutationCase in getMutationCases projectPath do
+        printfn "MUTATION\n\n%s" <| mutationCase.Patch
+        applyPatch mutationCase.Patch
+        runTest projectPath mutationCase.TestName
+        restore ()
+
     0

flake.lock

@@ -1,5 +1,47 @@
 {
   "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "git-temp-commit": {
+      "inputs": {
+        "flake-utils": [
+          "flake-utils"
+        ],
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1778481212,
+        "narHash": "sha256-Vy0ufQ51CHkamX+XB8hhgohBHJesKli0jF503NuSY20=",
+        "ref": "main",
+        "rev": "622b553f46920a2f3cc92f26c1f49cabb612de5f",
+        "revCount": 2,
+        "type": "git",
+        "url": "https://codeberg.org/svenvanheugten/git-temp-commit.git"
+      },
+      "original": {
+        "ref": "main",
+        "type": "git",
+        "url": "https://codeberg.org/svenvanheugten/git-temp-commit.git"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1776877367,
@@ -18,8 +60,25 @@
     },
     "root": {
       "inputs": {
+        "flake-utils": "flake-utils",
+        "git-temp-commit": "git-temp-commit",
         "nixpkgs": "nixpkgs"
       }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -1,57 +1,50 @@
 {
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    git-temp-commit = {
+      url = "git+https://codeberg.org/svenvanheugten/git-temp-commit.git?ref=main";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "flake-utils";
+    };
   };
 
   outputs =
-    { self, nixpkgs }:
-    let
-      systems = [
-        "x86_64-linux"
-        "aarch64-linux"
-        "x86_64-darwin"
-        "aarch64-darwin"
-      ];
-      forEachSystem =
-        f: nixpkgs.lib.genAttrs systems (system: f system (import nixpkgs { inherit system; }));
-    in
     {
-      formatter = forEachSystem (_system: pkgs: pkgs.nixfmt-rfc-style);
+      self,
+      nixpkgs,
+      flake-utils,
+      git-temp-commit,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        packages.default = pkgs.buildDotnetModule {
+          pname = "mutannot";
+          version = "0.1.0";
+          src = ./Mutannot;
+          projectFile = "Mutannot.fsproj";
+          nugetDeps = ./Mutannot/deps.nix;
+          executables = [ "mutannot" ];
+          dotnet-sdk = pkgs.dotnet-sdk_10;
+          dotnet-runtime = pkgs.dotnet-sdk_10;
+          useDotnetFromEnv = true;
 
-      packages = forEachSystem (
-        _system: pkgs:
-        let
-          mutannot = pkgs.buildDotnetModule {
-            pname = "mutannot";
-            version = "0.1.0";
-            src = ./Mutannot;
-            projectFile = "Mutannot.fsproj";
-            nugetDeps = ./Mutannot/deps.nix;
-            executables = [ "mutannot" ];
-            dotnet-sdk = pkgs.dotnet-sdk_10;
-            dotnet-runtime = pkgs.dotnet-sdk_10;
-            useDotnetFromEnv = true;
-
-            meta = {
-              mainProgram = "mutannot";
-            };
+          meta = {
+            mainProgram = "mutannot";
           };
-        in
-        {
-          default = mutannot;
-          mutannot = mutannot;
-        }
-      );
+        };
 
-      devShells = forEachSystem (
-        _system: pkgs: {
-          default = pkgs.mkShell {
-            packages = [
-              pkgs.git
-              pkgs.dotnet-sdk_10
-            ];
-          };
-        }
-      );
-    };
+        devShells.default = pkgs.mkShell {
+          packages = [
+            pkgs.git
+            pkgs.dotnet-sdk_10
+            git-temp-commit.packages.${system}.default
+          ];
+        };
+      }
+    );
 }