From 790ee8dc54b32cd53d5d5966ce5e46cd4d87e449 Mon Sep 17 00:00:00 2001
From: nojaf <florian.verdonck@outlook.com>
Date: Thu, 1 Jun 2023 11:30:29 +0200
Subject: [PATCH 1/2] Reuse synTypar names when typar is resolved.

---
 src/Compiler/Checking/CheckDeclarations.fs      | 12 +++++++++++-
 .../Signatures/TypeTests.fs                     | 17 +++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/Compiler/Checking/CheckDeclarations.fs b/src/Compiler/Checking/CheckDeclarations.fs
index 3c97ea8354e..d4c15029ff0 100644
--- a/src/Compiler/Checking/CheckDeclarations.fs
+++ b/src/Compiler/Checking/CheckDeclarations.fs
@@ -3948,7 +3948,17 @@ module TcDeclarations =
             let resInfo = TypeNameResolutionStaticArgsInfo.FromTyArgs synTypars.Length
             let _, tcref =
                 match ResolveTypeLongIdent cenv.tcSink cenv.nameResolver ItemOccurence.Binding OpenQualified envForDecls.NameEnv ad longPath resInfo PermitDirectReferenceToGeneratedType.No with
-                | Result res -> res
+                | Result res ->
+                    // Update resolved type parameters with the names from the source.
+                    let _, tcref = res
+                    if tcref.TyparsNoRange.Length = synTypars.Length then
+                        (tcref.TyparsNoRange, synTypars)
+                        ||> List.zip
+                        |> List.iter (fun (typar, SynTyparDecl.SynTyparDecl(_, SynTypar(ident = untypedIdent))) ->
+                            typar.SetIdent(untypedIdent)
+                        )
+
+                    res
                 | res when inSig && List.isSingleton longPath ->
                     errorR(Deprecated(FSComp.SR.tcReservedSyntaxForAugmentation(), m))
                     ForceRaise res
diff --git a/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs b/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
index d7f81a04f50..1014a4249c2 100644
--- a/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
+++ b/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
@@ -75,3 +75,20 @@ namespace Foo.Types
     val EndLine: int
 
     val EndColumn: int"""
+
+[<Fact>]
+let ``Type extension uses type parameters names from source`` () =
+    FSharp """
+module Extensions
+
+type List<'E> with
+
+    member this.X = this.Head
+"""
+    |> printSignatures
+    |> should equal
+        """
+module Extensions
+type List<'E> with
+
+  member X: 'E"""

From 7f4feaa472977ba1dc6b5910ff1c948cf982b3a9 Mon Sep 17 00:00:00 2001
From: nojaf <florian.verdonck@outlook.com>
Date: Thu, 1 Jun 2023 11:37:58 +0200
Subject: [PATCH 2/2] Add additional tests.

---
 .../Signatures/TypeTests.fs                   | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs b/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
index 1014a4249c2..0bf215a0dfd 100644
--- a/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
+++ b/tests/FSharp.Compiler.ComponentTests/Signatures/TypeTests.fs
@@ -92,3 +92,43 @@ module Extensions
 type List<'E> with
 
   member X: 'E"""
+
+[<Fact>]
+let ``Type extension with constraints uses type parameters names from source`` () =
+    FSharp """
+module Extensions
+
+type Map<'K, 'V when 'K: comparison> with
+
+    member m.X (t: 'T) (k: 'K) = Some k, ({| n = [|k|] |}, 0)
+"""
+    |> printSignatures
+    |> should equal
+        """
+module Extensions
+type Map<'K,'V when 'K: comparison> with
+
+  member X: t: 'T -> k: 'K -> 'K option * ({| n: 'K array |} * int) when 'K: comparison"""
+ 
+[<Fact>]
+let ``Type extension with lowercase type parameters names from source`` () =
+    FSharp """
+module Extensions
+
+open System.Collections.Concurrent
+
+type ConcurrentDictionary<'key, 'value> with
+
+  member x.TryFind key =
+    match x.TryGetValue key with
+    | true, value -> Some value
+    | _ -> None
+"""
+    |> printSignatures
+    |> should equal
+        """
+module Extensions
+type System.Collections.Concurrent.ConcurrentDictionary<'key,'value> with
+
+  member TryFind: key: 'key -> 'value option"""
+  
\ No newline at end of file