Fix #18086: suppress NuGet restore stdout under FSI --quiet

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -68,6 +68,7 @@
 * Allow `| null` nullable annotation on a `[<MeasureAnnotatedAbbreviation>]` over a reference type (e.g. the FSharp.UMX `type string<[<Measure>] 'm> = string` pattern). ([Issue #19657](https://github.com/dotnet/fsharp/issues/19657))
 * Fix `[<Struct>] ?param` optional parameters could not be passed using the explicit `?param = expr` caller-side syntax with a `ValueOption` value. ([Issue #19711](https://github.com/dotnet/fsharp/issues/19711), [PR #19742](https://github.com/dotnet/fsharp/pull/19742))
 * Fix signature conformance: overloaded member with unit parameter `M(())` now matches sig `member M: unit -> unit`. ([Issue #19596](https://github.com/dotnet/fsharp/issues/19596), [PR #19615](https://github.com/dotnet/fsharp/pull/19615))
+* Fix `--quiet` not suppressing NuGet restore output on stdout in F# Interactive ([Issue #18086](https://github.com/dotnet/fsharp/issues/18086))
 * Reference assembly MVIDs are now deterministic across compiler invocations. Previously, `--refout` / `<ProduceReferenceAssembly>true</ProduceReferenceAssembly>` produced a different MVID every build because the implied signature hash used .NET's randomized `String.GetHashCode()`. ([Issue #19751](https://github.com/dotnet/fsharp/issues/19751), [PR #19801](https://github.com/dotnet/fsharp/pull/19801))
 * Parser: recover on unfinished if and binary expressions
 ([PR #19724](https://github.com/dotnet/fsharp/pull/19724))

src/Compiler/Interactive/fsi.fs

@@ -2819,8 +2819,12 @@ type internal FsiDynamicCompiler
 
                             if result.Success then
 
+                                // Under --quiet, route NuGet restore stdout to stderr.
+                                let stdOutSink: System.IO.TextWriter =
+                                    if tcConfigB.noFeedback then Console.Error else Console.Out
+
                                 for line in result.StdOut do
-                                    Console.Out.WriteLine(line)
+                                    stdOutSink.WriteLine(line)
 
                                 for line in result.StdError do
                                     Console.Error.WriteLine(line)

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

@@ -67,3 +67,50 @@ module FsiCliTests =
         let result = runFsiProcess [option]
         Assert.NotEqual(0, result.ExitCode)
         Assert.Contains(expectedError, result.StdErr)
+
+    // ============================================================================
+    // Issue #18086: --quiet must suppress NuGet restore stdout chatter
+    // ============================================================================
+
+    let private writeTempScript (content: string) : string =
+        let path = System.IO.Path.Combine(System.IO.Path.GetTempPath(), $"fsi_quiet_{System.Guid.NewGuid():N}.fsx")
+        System.IO.File.WriteAllText(path, content)
+        path
+
+    let private runFsiScript (extraArgs: string list) (scriptBody: string) =
+        let scriptPath = writeTempScript scriptBody
+        try
+            let result = runFsiProcess (extraArgs @ [scriptPath])
+            result
+        finally
+            try System.IO.File.Delete(scriptPath) with _ -> ()
+
+    [<Fact>]
+    let ``FSI quiet mode suppresses NuGet restore output from stdout`` () =
+        let script = """
+#r "nuget: Newtonsoft.Json, 13.0.3"
+printfn "RESULT_MARKER_18086"
+"""
+        let result = runFsiScript ["--quiet"] script
+        Assert.Equal(0, result.ExitCode)
+        Assert.Contains("RESULT_MARKER_18086", result.StdOut)
+        Assert.DoesNotContain("Determining projects to restore", result.StdOut)
+        Assert.DoesNotContain("Restored ", result.StdOut)
+        Assert.DoesNotContain("NU1", result.StdOut)
+
+    [<Fact>]
+    let ``FSI default (non-quiet) mode still evaluates script and prints user output`` () =
+        let script = """
+#r "nuget: Newtonsoft.Json, 13.0.3"
+printfn "RESULT_MARKER_18086_DEFAULT"
+"""
+        let result = runFsiScript [] script
+        Assert.Equal(0, result.ExitCode)
+        Assert.Contains("RESULT_MARKER_18086_DEFAULT", result.StdOut)
+
+    [<Fact>]
+    let ``FSI quiet mode still prints user printfn output to stdout`` () =
+        let script = """printfn "hello from quiet script" """
+        let result = runFsiScript ["--quiet"] script
+        Assert.Equal(0, result.ExitCode)
+        Assert.Contains("hello from quiet script", result.StdOut)