Wrap hash postfix type in parentheses.

src/Compiler/Checking/NicePrint.fs

@@ -708,7 +708,15 @@ module PrintTypes =
         match Zmap.tryFind typar env.inplaceConstraints with
         | Some typarConstraintTy ->
             if Zset.contains typar env.singletons then
-                leftL (tagPunctuation "#") ^^ layoutTypeWithInfo denv env typarConstraintTy
+                let tyLayout =
+                    match typarConstraintTy with
+                    | TType_app (tyconRef = tc; typeInstantiation = ti)
+                        when ti.Length > 0 && not (usePrefix denv tc) ->
+                        layoutTypeWithInfo denv env typarConstraintTy
+                        |> bracketL
+                    | _ -> layoutTypeWithInfo denv env typarConstraintTy
+
+                leftL (tagPunctuation "#") ^^ tyLayout
             else
                 (varL ^^ sepL (tagPunctuation ":>") ^^ layoutTypeWithInfo denv env typarConstraintTy) |> bracketL
 

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

@@ -251,6 +251,7 @@
     <Compile Include="Signatures\SigGenerationRoundTripTests.fs" />
     <Compile Include="Signatures\NestedTypeTests.fs" />
     <Compile Include="Signatures\MissingDiagnostic.fs" />
+    <Compile Include="Signatures\HashConstraintTests.fs" />
     <Compile Include="StaticLinking\StaticLinking.fs" />
     <Compile Include="FSharpChecker\CommonWorkflows.fs" />
     <Compile Include="FSharpChecker\SymbolUse.fs" />

tests/FSharp.Compiler.ComponentTests/Signatures/ArrayTests.fs

@@ -1,4 +1,4 @@
-module Signatures.SignatureTests
+module Signatures.ArrayTests
 
 open Xunit
 open Signatures.TestHelpers

tests/FSharp.Compiler.ComponentTests/Signatures/HashConstraintTests.fs

@@ -0,0 +1,33 @@
+module Signatures.HashConstraintTests
+
+open Xunit
+open FsUnit
+open FSharp.Test.Compiler
+open Signatures.TestHelpers
+
+[<Fact>]
+let ``Optional hash constraint`` () =
+    FSharp
+        """
+module Foo
+
+[<Interface>]
+type Node =
+    abstract Children: int array
+
+let noa<'n when 'n :> Node> (n: 'n option) =
+    match n with
+    | None -> Array.empty
+    | Some n -> [| n :> Node |]
+"""
+    |> printSignatures
+    |> should
+        equal
+        """
+module Foo
+
+type Node =
+
+  abstract Children: int array
+
+val noa: n: #Node option -> Node array"""

tests/FSharp.Compiler.ComponentTests/Signatures/MissingDiagnostic.fs

@@ -1,4 +1,4 @@
-module FSharp.Compiler.ComponentTests.Signatures.MissingDiagnostic
+module Signatures.MissingDiagnostic
 
 open Xunit
 open FSharp.Test

tests/FSharp.Compiler.ComponentTests/Signatures/SigGenerationRoundTripTests.fs

@@ -28,7 +28,7 @@ let ``Generate and compile`` implFileName =
     |> withLangVersionPreview
     |> withDefines ["TESTS_AS_APP";"COMPILED"]
     |> ignoreWarnings
+    |> withOptions [ "--warnaserror:64" ]
     |> asExe
     |> compile
     |> shouldSucceed
-

tests/FSharp.Compiler.ComponentTests/Signatures/TestCasesForGenerationRoundTrip/hash_constraint_seq.fsx

@@ -0,0 +1,7 @@
+module Foo
+
+open System
+open System.Threading.Tasks
+
+let mapWithAdditionalDependenies
+    (mapping: 'a -> 'b * #seq<#IDisposable>) = 0