Revert "disable cosmetic typar overwrite in type extensions"

This reverts commit 15fbf8f.

Author: majocha

src/Compiler/Checking/CheckDeclarations.fs

@@ -4220,20 +4220,18 @@ module TcDeclarations =
                 | Result res ->
                     // Update resolved type parameters with the names from the source.
                     let _, tcref, _ = res
-
-                    // Disabled to allow deterministic parallel type checking. See https://github.com/dotnet/fsharp/issues/19033
-                    // TODO: mutating typar here can lead to a race during parallel type checking.
-                    // Some type extensions can end up with a wrong type argument name.
-                    // This will break deterministic builds.
 
-                    //if tcref.TyparsNoRange.Length = synTypars.Length then
-                    //    (tcref.TyparsNoRange, synTypars)
-                    //    ||> List.zip
-                    //    |> List.iter (fun (typar, SynTyparDecl.SynTyparDecl (typar = tp)) ->
-                    //        let (SynTypar(ident = untypedIdent; staticReq = sr)) = tp
-                    //        if typar.StaticReq = sr then
-                    //            typar.SetIdent(untypedIdent)
-                    //    )
+                    if tcref.TyparsNoRange.Length = synTypars.Length then
+                        (tcref.TyparsNoRange, synTypars)
+                        ||> List.zip
+                        |> List.iter (fun (typar, SynTyparDecl.SynTyparDecl (typar = tp)) ->
+                            let (SynTypar(ident = untypedIdent; staticReq = sr)) = tp
+                            if typar.StaticReq = sr then
+                                // TODO: mutating typar here can lead to a race during parallel type checking.
+                                // Some type extensions can end up with a wrong type argument name.
+                                // This will break deterministic builds.
+                                typar.SetIdent(untypedIdent)
+                        )
 
                     tcref
 

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

@@ -76,8 +76,7 @@ namespace Foo.Types
 
     val EndColumn: int"""
 
-// See https://github.com/dotnet/fsharp/issues/19033
-[<Fact(Skip="needs fixing")>]
+[<Fact>]
 let ``Type extension uses type parameters names from source`` () =
     FSharp """
 module Extensions
@@ -94,8 +93,7 @@ type List<'E> with
 
   member X: 'E"""
 
-// See https://github.com/dotnet/fsharp/issues/19033
-[<Fact(Skip="needs fixing")>]
+[<Fact>]
 let ``Type extension with constraints uses type parameters names from source`` () =
     FSharp """
 module Extensions
@@ -112,8 +110,7 @@ type Map<'K,'V when 'K: comparison> with
 
   member X: t: 'T -> k: 'K -> 'K option * ({| n: 'K array |} * int) when 'K: comparison"""
 
-// See https://github.com/dotnet/fsharp/issues/19033
-[<Fact(Skip="needs fixing")>]
+[<Fact>]
 let ``Type extension with lowercase type parameters names from source`` () =
     FSharp """
 module Extensions