Add FSI options tests and wire up CLI test infrastructure

Add runFsiProcess/runFscProcess subprocess helpers to Compiler.fs and
include the existing CLI test files (FsiCliTests.fs, FscCliTests.fs,
CliProcessTests.fs) in the project build.

Add 19 new tests covering --quiet, --exec, --use, --load, --gui,
--readline, --quotations-debug, --shadowcopyreferences, --nologo,
and error cases for unknown options and invalid --warn levels.

Contributes to #13878

Author: bbatsov

tests/FSharp.Compiler.ComponentTests/CompilerOptions/Fsc/FscCliTests.fs

@@ -34,7 +34,7 @@ module FscCliTests =
     /// Original: SOURCE="E_MissingSourceFile02.fs X:\doesnotexist.fs"
     /// Expected: //<Expects id="FS0225" status="error">Source file ['"].+['"] could not be found</Expects>
     /// CLI Test: FSC with non-existent absolute path (Windows-style)
-    [<FactForWINDOWS>]
+    [<FactForDESKTOP>]
     let ``fsc missing source file - absolute Windows path reports FS0225`` () =
         let result = runFscProcess ["X:\\doesnotexist.fs"]
         Assert.NotEqual(0, result.ExitCode)
@@ -54,7 +54,7 @@ module FscCliTests =
     /// Original: SOURCE="E_MissingSourceFile03.fs \\qwerty\y\doesnotexist.fs"
     /// Expected: //<Expects id="FS0225" status="error">Source file ['"].+['"] could not be found</Expects>
     /// CLI Test: FSC with non-existent UNC path
-    [<FactForWINDOWS>]
+    [<FactForDESKTOP>]
     let ``fsc missing source file - UNC path reports FS0225`` () =
         let result = runFscProcess ["\\\\qwerty\\y\\doesnotexist.fs"]
         Assert.NotEqual(0, result.ExitCode)

tests/FSharp.Compiler.ComponentTests/CompilerOptions/fsi/FsiCliTests.fs

@@ -2,6 +2,8 @@
 
 namespace CompilerOptions.Fsi
 
+open System
+open System.IO
 open Xunit
 open FSharp.Test
 open FSharp.Test.Compiler
@@ -110,3 +112,197 @@ module FsiCliTests =
         // FSI should report error for unrecognized option
         Assert.NotEqual(0, result.ExitCode)
         Assert.Contains("Unrecognized option: '--subsystemversion'", result.StdErr)
+
+    // ============================================================================
+    // --quiet option tests
+    // ============================================================================
+
+    /// CLI Test: --quiet suppresses the banner
+    [<Fact>]
+    let ``fsi quiet - suppresses banner`` () =
+        let result = runFsiProcess ["--quiet"; "--exec"; "--nologo"]
+        Assert.Equal(0, result.ExitCode)
+        Assert.DoesNotContain("Microsoft (R) F# Interactive", result.StdOut)
+
+    /// In-process test: --quiet suppresses feedback output but expressions still evaluate
+    [<Fact>]
+    let ``fsi quiet - expressions evaluate correctly`` () =
+        Fsx """let x = 1 + 1"""
+        |> withOptions ["--quiet"]
+        |> runFsi
+        |> shouldSucceed
+
+    // ============================================================================
+    // --exec option tests
+    // ============================================================================
+
+    /// CLI Test: --exec causes FSI to exit after evaluating (no interactive prompt)
+    [<Fact>]
+    let ``fsi exec - exits after evaluating script`` () =
+        let tmpFile = Path.Combine(Path.GetTempPath(), $"fsi_exec_test_{Guid.NewGuid()}.fsx")
+        try
+            File.WriteAllText(tmpFile, "printfn \"hello from exec\"")
+            let result = runFsiProcess ["--exec"; "--nologo"; tmpFile]
+            Assert.Equal(0, result.ExitCode)
+            Assert.Contains("hello from exec", result.StdOut)
+        finally
+            try File.Delete(tmpFile) with _ -> ()
+
+    // ============================================================================
+    // --use option tests
+    // ============================================================================
+
+    /// CLI Test: --use:file.fsx loads and executes a script file
+    [<Fact>]
+    let ``fsi use - loads and executes script file`` () =
+        let tmpFile = Path.Combine(Path.GetTempPath(), $"fsi_use_test_{Guid.NewGuid()}.fsx")
+        try
+            File.WriteAllText(tmpFile, "printfn \"loaded via use\"")
+            let result = runFsiProcess ["--nologo"; "--exec"; $"--use:{tmpFile}"]
+            Assert.Equal(0, result.ExitCode)
+            Assert.Contains("loaded via use", result.StdOut)
+        finally
+            try File.Delete(tmpFile) with _ -> ()
+
+    /// CLI Test: --use with nonexistent file produces error
+    [<Fact>]
+    let ``fsi use - nonexistent file produces error`` () =
+        let result = runFsiProcess ["--exec"; "--use:nonexistent_file_xyz.fsx"]
+        Assert.NotEqual(0, result.ExitCode)
+
+    // ============================================================================
+    // --load option tests
+    // ============================================================================
+
+    /// CLI Test: --load:file.fsx loads a file (definitions available)
+    [<Fact>]
+    let ``fsi load - loads file definitions`` () =
+        let tmpFile = Path.Combine(Path.GetTempPath(), $"fsi_load_test_{Guid.NewGuid()}.fsx")
+        try
+            File.WriteAllText(tmpFile, "let loadedValue = 42")
+            let result = runFsiProcess ["--nologo"; "--exec"; $"--load:{tmpFile}"]
+            Assert.Equal(0, result.ExitCode)
+        finally
+            try File.Delete(tmpFile) with _ -> ()
+
+    /// CLI Test: --load with nonexistent file produces error
+    [<Fact>]
+    let ``fsi load - nonexistent file produces error`` () =
+        let result = runFsiProcess ["--exec"; "--load:nonexistent_file_xyz.fsx"]
+        Assert.NotEqual(0, result.ExitCode)
+
+    // ============================================================================
+    // --gui option tests (switch: +/-)
+    // ============================================================================
+
+    /// CLI Test: --gui- is accepted without error
+    [<Fact>]
+    let ``fsi gui - gui minus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--gui-"]
+        |> runFsi
+        |> shouldSucceed
+
+    /// CLI Test: --gui+ is accepted without error
+    [<Fact>]
+    let ``fsi gui - gui plus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--gui+"]
+        |> runFsi
+        |> shouldSucceed
+
+    // ============================================================================
+    // --readline option tests (switch: +/-)
+    // ============================================================================
+
+    /// CLI Test: --readline- is accepted without error
+    [<Fact>]
+    let ``fsi readline - readline minus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--readline-"]
+        |> runFsi
+        |> shouldSucceed
+
+    /// CLI Test: --readline+ is accepted without error
+    [<Fact>]
+    let ``fsi readline - readline plus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--readline+"]
+        |> runFsi
+        |> shouldSucceed
+
+    // ============================================================================
+    // --quotations-debug option tests (switch: +/-)
+    // ============================================================================
+
+    /// CLI Test: --quotations-debug+ is accepted without error
+    [<Fact>]
+    let ``fsi quotations-debug - plus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--quotations-debug+"]
+        |> runFsi
+        |> shouldSucceed
+
+    /// CLI Test: --quotations-debug- is accepted without error
+    [<Fact>]
+    let ``fsi quotations-debug - minus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--quotations-debug-"]
+        |> runFsi
+        |> shouldSucceed
+
+    // ============================================================================
+    // --shadowcopyreferences option tests (switch: +/-)
+    // ============================================================================
+
+    /// CLI Test: --shadowcopyreferences+ is accepted without error
+    [<Fact>]
+    let ``fsi shadowcopyreferences - plus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--shadowcopyreferences+"]
+        |> runFsi
+        |> shouldSucceed
+
+    /// CLI Test: --shadowcopyreferences- is accepted without error
+    [<Fact>]
+    let ``fsi shadowcopyreferences - minus accepted`` () =
+        Fsx """1+1"""
+        |> withOptions ["--shadowcopyreferences-"]
+        |> runFsi
+        |> shouldSucceed
+
+    // ============================================================================
+    // --nologo option tests
+    // ============================================================================
+
+    /// CLI Test: --nologo suppresses the banner
+    [<Fact>]
+    let ``fsi nologo - suppresses banner in subprocess`` () =
+        let result = runFsiProcess ["--nologo"; "--exec"]
+        Assert.Equal(0, result.ExitCode)
+        Assert.DoesNotContain("Microsoft (R) F# Interactive", result.StdOut)
+
+    /// In-process test: FSI without --nologo shows the banner
+    [<Fact>]
+    let ``fsi nologo - without nologo shows banner`` () =
+        Fsx """1+1"""
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "Microsoft"
+
+    // ============================================================================
+    // Additional error case tests
+    // ============================================================================
+
+    /// CLI Test: completely unknown option produces FS0243
+    [<Fact>]
+    let ``fsi error - unknown option produces FS0243`` () =
+        let result = runFsiProcess ["--not-a-real-option"]
+        Assert.NotEqual(0, result.ExitCode)
+        Assert.Contains("Unrecognized option: '--not-a-real-option'", result.StdErr)
+
+    /// CLI Test: --warn with invalid level produces error
+    [<Fact>]
+    let ``fsi error - invalid warn level produces error`` () =
+        let result = runFsiProcess ["--warn:invalid"; "--exec"]
+        Assert.NotEqual(0, result.ExitCode)

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -320,6 +320,9 @@
     <Compile Include="CompilerOptions\fsc\reflectionfree.fs" />
     <Compile Include="CompilerOptions\fsc\refonlyrefout.fs" />
     <Compile Include="CompilerOptions\fsc\sourceFiles.fs" />
+    <Compile Include="CompilerOptions\fsc\FscCliTests.fs" />
+    <Compile Include="CompilerOptions\fsi\FsiCliTests.fs" />
+    <Compile Include="CompilerOptions\CliProcessTests.fs" />
     <Compile Include="CompilerService\RangeModule.fs" />
     <Compile Include="CompilerService\Caches.fs" />
     <Compile Include="CompilerService\LruCache.fs" />

tests/FSharp.Test.Utilities/Compiler.fs

@@ -2074,3 +2074,36 @@ Actual:
         match hash with
         | Some h -> h
         | None -> failwith "Implied signature hash returned 'None' which should not happen"
+
+    // ========================================================================
+    // CLI subprocess helpers for testing options that cause FSI/FSC to exit
+    // (e.g. --help, unrecognized options, missing files).
+    // These cannot be tested in-process because the process exits before
+    // a session is created.
+    // ========================================================================
+
+    type CliProcessResult =
+        { ExitCode: int
+          StdOut: string
+          StdErr: string }
+
+    let private runCliProcess (toolDll: string) (args: string list) : CliProcessResult =
+        let envVars = Map.ofList [ "DOTNET_ROLL_FORWARD", "LatestMajor"
+                                   "DOTNET_ROLL_FORWARD_TO_PRERELEASE", "1" ]
+        let cfg = config "Debug" envVars
+        let dotnet = cfg.DotNetExe
+        let allArgs = toolDll :: args |> String.concat " "
+        let exitCode, stdout, stderr = Commands.executeProcess dotnet allArgs (Directory.GetCurrentDirectory())
+        { ExitCode = exitCode; StdOut = stdout; StdErr = stderr }
+
+    let runFsiProcess (args: string list) : CliProcessResult =
+        let envVars = Map.ofList [ "DOTNET_ROLL_FORWARD", "LatestMajor"
+                                   "DOTNET_ROLL_FORWARD_TO_PRERELEASE", "1" ]
+        let cfg = config "Debug" envVars
+        runCliProcess cfg.FSI args
+
+    let runFscProcess (args: string list) : CliProcessResult =
+        let envVars = Map.ofList [ "DOTNET_ROLL_FORWARD", "LatestMajor"
+                                   "DOTNET_ROLL_FORWARD_TO_PRERELEASE", "1" ]
+        let cfg = config "Debug" envVars
+        runCliProcess cfg.FSC args