[Repo Assist] fix: improve delegate type tooltips using FSharpDelegateSignature API

src/FsAutoComplete.Core/DocumentationFormatter.fs

@@ -641,11 +641,25 @@ module DocumentationFormatter =
           |> String.concat ($"{nl}  | "))
 
     let delegateTip () =
-      let invoker =
-        fse.MembersFunctionsAndValues |> Seq.find (fun f -> f.DisplayName = "Invoke")
+      let delegateSig = fse.FSharpDelegateSignature
 
-      let invokerSig = getFuncSignatureWithIdent displayContext invoker 6
-      $" ={nl}   delegate of{nl}{invokerSig}"
+      let args =
+        if delegateSig.DelegateArguments.Count = 0 then
+          "unit"
+        else
+          delegateSig.DelegateArguments
+          |> Seq.map (fun (name, ty) ->
+            let typeName = ty |> format displayContext |> fst
+
+            match name with
+            | Some n when not (String.IsNullOrWhiteSpace n) ->
+              let n = FSharpKeywords.NormalizeIdentifierBackticks n
+              $"{n}: {typeName}"
+            | _ -> typeName)
+          |> String.concat " * "
+
+      let retType = delegateSig.DelegateReturnType |> format displayContext |> fst
+      $" ={nl}   delegate of {args} -> {retType}"
 
     let typeTip () =
       let constructors =

src/FsAutoComplete.Core/SignatureFormatter.fs

@@ -707,11 +707,25 @@ module SignatureFormatter =
           |> String.concat $"{nl}  | ")
 
     let delegateTip () =
-      let invoker =
-        fse.MembersFunctionsAndValues |> Seq.find (fun f -> f.DisplayName = "Invoke")
+      let delegateSig = fse.FSharpDelegateSignature
 
-      let invokerSig = getFuncSignatureWithIdent displayContext invoker 6
-      $" ={nl}   delegate of{nl}{invokerSig}"
+      let args =
+        if delegateSig.DelegateArguments.Count = 0 then
+          "unit"
+        else
+          delegateSig.DelegateArguments
+          |> Seq.map (fun (name, ty) ->
+            let typeName = formatFSharpType displayContext ty
+
+            match name with
+            | Some n when not (String.IsNullOrWhiteSpace n) ->
+              let n = FSharpKeywords.NormalizeIdentifierBackticks n
+              $"{n}: {typeName}"
+            | _ -> typeName)
+          |> String.concat " * "
+
+      let retType = formatFSharpType displayContext delegateSig.DelegateReturnType
+      $" ={nl}   delegate of {args} -> {retType}"
 
     let typeTip () =
       let constructors =

test/FsAutoComplete.Tests.Lsp/CoreTests.fs

@@ -610,10 +610,21 @@ let tooltipTests state =
           // Hover must show `string | null`, not just `string`.
           verifySignature 113u 4u "val nullableStringVal: string | null"
 
+          verifySignature 114u 4u (concatLines [ "val returnsNullable:"; "   s: string"; "   -> string | null" ])
+
+          // Delegate tooltip format — regression for issue #627.
+          // Verify that hovering on a delegate type definition shows a clean
+          // "delegate of <args> -> <retType>" signature rather than broken output.
+          verifySignature 117u 5u (concatLines [ "type NoArgDelegate ="; "   delegate of unit -> unit" ])
+
+          verifySignature 118u 5u (concatLines [ "type SingleArgDelegate ="; "   delegate of arg: string -> int" ])
+
           verifySignature
-            114u
-            4u
-            (concatLines [ "val returnsNullable:"; "   s: string"; "   -> string | null" ]) ] ]
+            119u
+            5u
+            (concatLines [ "type MultiArgDelegate ="; "   delegate of a: string * b: int -> bool" ])
+
+          verifySignature 120u 5u (concatLines [ "type UnannotatedDelegate ="; "   delegate of string -> int" ]) ] ]
 
 let closeTests state =
   // Note: clear diagnostics also implies clear caches (-> remove file & project options from State).

test/FsAutoComplete.Tests.Lsp/InfoPanelTests.fs

@@ -60,4 +60,24 @@ let docFormattingTest state =
           | Result.Ok(Some(As(model: FsAutoComplete.CommandResponse.DocumentationDescription))) ->
             Expect.stringContains model.Signature "'T1 * 'T2 * 'T3" "Formatted doc contains 3 params separated by ( * )"
           | Result.Ok _ -> failtest "couldn't parse doc as the json type we expected"
+        })
+
+      testCaseAsync
+        "Delegate type shows clean 'delegate of <args> -> <ret>' signature (issue #627)"
+        (async {
+          let! (server, path) = server
+
+          // Line 3 (0-indexed), char 5: hovering on "DelegateWithArgs" type name
+          let! doc =
+            server.FSharpDocumentation
+              { TextDocument = { Uri = path }
+                Position = { Character = 5u; Line = 3u } }
+
+          match doc with
+          | Result.Error err -> failtest $"Doc error: {err.Message}"
+          | Result.Ok(Some(As(model: FsAutoComplete.CommandResponse.DocumentationDescription))) ->
+            Expect.stringContains model.Signature "delegate of" "Delegate signature should contain 'delegate of'"
+            Expect.stringContains model.Signature "name" "Delegate signature should contain parameter name 'name'"
+            Expect.stringContains model.Signature "count" "Delegate signature should contain parameter name 'count'"
+          | Result.Ok _ -> failtest "couldn't parse doc as the json type we expected"
         }) ]

test/FsAutoComplete.Tests.Lsp/TestCases/FormattedDocumentation/Script.fsx

@@ -1,2 +1,4 @@
 Map.map
-List.unzip3
+List.unzip3
+// Delegate type for issue #627 tooltip tests
+type DelegateWithArgs = delegate of name: string * count: int -> bool

test/FsAutoComplete.Tests.Lsp/TestCases/Tooltips/Script.fsx

@@ -113,3 +113,9 @@ let functionAliasValue: FunctionAlias = fun _ -> 2
 // Nullable reference types (F# 9 | null syntax) — issue #1352
 let nullableStringVal: string | null = null
 let returnsNullable (s: string) : string | null = null
+
+// Delegate types — hover tooltip regression for issue #627
+type NoArgDelegate = delegate of unit -> unit
+type SingleArgDelegate = delegate of arg: string -> int
+type MultiArgDelegate = delegate of a: string * b: int -> bool
+type UnannotatedDelegate = delegate of string -> int