Fix preferreduilang switch leaking into fsi.CommandLineArgs

src/Compiler/Interactive/fsi.fs

@@ -1068,8 +1068,41 @@ type internal FsiCommandLineOptions(fsi: FsiEvaluationSessionHostConfig, argv: s
                             (fun args ->
                                 let scriptFile = args[0]
                                 let scriptArgs = List.tail args
+
+                                // Filter out and process preferreduilang from script args
+                                let isPreferredUiLangArg (arg: string) =
+                                    arg.StartsWith("--preferreduilang:", StringComparison.OrdinalIgnoreCase)
+                                    || arg.StartsWith("/preferreduilang:", StringComparison.OrdinalIgnoreCase)
+
+                                let rec filterScriptArgs (args: string list) =
+                                    match args with
+                                    | [] -> []
+                                    | (arg: string) :: rest when isPreferredUiLangArg arg ->
+                                        // Extract culture and set it
+                                        let colonIndex = arg.IndexOf(':')
+
+                                        if colonIndex >= 0 && colonIndex < arg.Length - 1 then
+                                            let culture = arg.Substring(colonIndex + 1)
+
+                                            try
+                                                // Validate culture first by creating CultureInfo
+                                                let cultureInfo = CultureInfo(culture)
+                                                // Only set if valid
+                                                tcConfigB.preferredUiLang <- Some culture
+                                                Thread.CurrentThread.CurrentUICulture <- cultureInfo
+                                            with
+                                            | :? CultureNotFoundException
+                                            | :? ArgumentException ->
+                                                // Ignore invalid culture, just don't set it
+                                                ()
+
+                                        filterScriptArgs rest
+                                    | arg :: rest -> arg :: filterScriptArgs rest
+
+                                let filteredScriptArgs = filterScriptArgs scriptArgs
+
                                 inputFilesAcc <- inputFilesAcc @ [ (scriptFile, true) ] (* record script.fsx for evaluation *)
-                                List.iter recordExplicitArg scriptArgs (* record rest of line as explicit arguments *)
+                                List.iter recordExplicitArg filteredScriptArgs (* record rest of line as explicit arguments *)
                                 tcConfigB.noFeedback <- true (* "quiet", no banners responses etc *)
                                 interact <- false (* --exec, exit after eval *)
                                 [] (* no arguments passed on, all consumed here *)

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

@@ -277,6 +277,7 @@
     <Compile Include="Interop\Literals.fs" />
     <Compile Include="Scripting\Interactive.fs" />
     <Compile Include="Scripting\TypeCheckOnlyTests.fs" />
+    <Compile Include="Scripting\PreferredUiLangTests.fs" />
     <Compile Include="TypeChecks\TypeRelations.fs" />
     <Compile Include="TypeChecks\SeqTypeCheckTests.fs" />
     <Compile Include="TypeChecks\CheckDeclarationsTests.fs" />

tests/FSharp.Compiler.ComponentTests/Scripting/PreferredUiLangTests.fs

@@ -0,0 +1,147 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Scripting
+
+open Xunit
+open System
+open System.IO
+open FSharp.Test
+open FSharp.Test.CompilerAssertHelpers
+open FSharp.Compiler.Interactive.Shell
+open FSharp.Compiler.Diagnostics
+
+module ``PreferredUiLang tests`` =
+
+    [<Fact>]
+    let ``preferreduilang switch before script is consumed from CommandLineArgs``() =
+        let scriptContent = """
+printfn "Args: %A" fsi.CommandLineArgs
+if fsi.CommandLineArgs.Length <> 2 then exit 1
+if fsi.CommandLineArgs.[0] <> __SOURCE_FILE__ then exit 1
+if fsi.CommandLineArgs.[1] <> "arg1" then exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| "--preferreduilang:es-ES"; tmpFile; "arg1" |] 
+                    ""
+
+            // Should succeed (exit 0)
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)
+
+    [<Fact>]
+    let ``preferreduilang switch after script is consumed from CommandLineArgs``() =
+        let scriptContent = """
+printfn "Args: %A" fsi.CommandLineArgs
+if fsi.CommandLineArgs.Length <> 2 then exit 1
+if fsi.CommandLineArgs.[0] <> __SOURCE_FILE__ then exit 1
+if fsi.CommandLineArgs.[1] <> "arg1" then exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| tmpFile; "--preferreduilang:es-ES"; "arg1" |] 
+                    ""
+
+            // Should succeed (exit 0)
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)
+
+    [<Fact>]
+    let ``preferreduilang with slash form is consumed from CommandLineArgs``() =
+        let scriptContent = """
+printfn "Args: %A" fsi.CommandLineArgs
+if fsi.CommandLineArgs.Length <> 2 then exit 1
+if fsi.CommandLineArgs.[0] <> __SOURCE_FILE__ then exit 1
+if fsi.CommandLineArgs.[1] <> "arg1" then exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| tmpFile; "/preferreduilang:de-DE"; "arg1" |] 
+                    ""
+
+            // Should succeed (exit 0)
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)
+
+    [<Fact>]
+    let ``preferreduilang sets CurrentUICulture correctly``() =
+        let scriptContent = """
+let culture = System.Threading.Thread.CurrentThread.CurrentUICulture.Name
+printfn "Culture: %s" culture
+if not (culture.StartsWith("fr-FR")) then 
+    printfn "Expected culture starting with fr-FR, got: %s" culture
+    exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| "--preferreduilang:fr-FR"; tmpFile |] 
+                    ""
+
+            // Should succeed (exit 0)
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)
+
+    [<Fact>]
+    let ``preferreduilang after script also sets culture``() =
+        let scriptContent = """
+let culture = System.Threading.Thread.CurrentThread.CurrentUICulture.Name
+printfn "Culture: %s" culture
+if not (culture.StartsWith("ja-JP")) then 
+    printfn "Expected culture starting with ja-JP, got: %s" culture
+    exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| tmpFile; "--preferreduilang:ja-JP" |] 
+                    ""
+
+            // Should succeed (exit 0)
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)
+
+    [<Fact>]
+    let ``invalid culture in preferreduilang is ignored gracefully``() =
+        let scriptContent = """
+printfn "Args: %A" fsi.CommandLineArgs
+if fsi.CommandLineArgs.Length <> 2 then exit 1
+if fsi.CommandLineArgs.[0] <> __SOURCE_FILE__ then exit 1
+if fsi.CommandLineArgs.[1] <> "arg1" then exit 1
+exit 0
+"""
+        let tmpFile = Path.GetTempFileName() + ".fsx"
+        try
+            File.WriteAllText(tmpFile, scriptContent)
+            let errors, _, _ = 
+                CompilerAssert.RunScriptWithOptionsAndReturnResult 
+                    [| tmpFile; "--preferreduilang:invalid-culture-xyz"; "arg1" |] 
+                    ""
+
+            // Should succeed - invalid culture is ignored, but switch is still consumed
+            Assert.True((errors: ResizeArray<string>).Count = 0, sprintf "Expected no errors, got: %A" errors)
+        finally
+            if File.Exists(tmpFile) then File.Delete(tmpFile)