Add constraints to return types inner generics (#1342)

src/FsAutoComplete.Core/SignatureFormatter.fs

@@ -249,16 +249,24 @@ module SignatureFormatter =
         "Unknown"
 
     let retTypeConstraint =
-      if func.ReturnParameter.Type.IsGenericParameter then
-        let formattedParam =
-          formatGenericParameter false displayContext func.ReturnParameter.Type.GenericParameter
+      let genericParamConstraints = ResizeArray<string>()
 
-        if String.IsNullOrWhiteSpace formattedParam then
-          formattedParam
+      let rec getGenericParameters  (f : FSharpType) =
+        if f.IsGenericParameter then
+          let formattedParam = formatGenericParameter false displayContext f.GenericParameter
+          if not <| String.IsNullOrWhiteSpace formattedParam then
+            genericParamConstraints.Add formattedParam
         else
-          "(requires " + formattedParam + " )"
+          try
+            f.GenericArguments |> Seq.iter getGenericParameters
+          with
+            | e -> () // Sometimes GenericArguments throws an exception when accessing it
+
+      getGenericParameters func.ReturnParameter.Type
+      if Seq.isEmpty genericParamConstraints then ""
       else
-        ""
+        let formattedParam = genericParamConstraints |> String.join " and " |> _.Trim()
+        "(requires " + formattedParam + ")"
 
     let safeParameterName (p: FSharpParameter) =
       match Option.defaultValue p.DisplayNameCore p.Name with

test/FsAutoComplete.Tests.Lsp/CoreTests.fs

@@ -431,6 +431,22 @@ let tooltipTests state =
                 "   input: Expr"
                 "       -> option<objnull * System.Type>" ])
 #endif
+          verifySignature
+            77u
+            5u
+             (concatLines [
+                "val testIWSAMTest:"
+                "      unit"
+                "   -> Result<string,'e> (requires :> IWSAMTest<'e>)"
+             ])
+          verifySignature
+            90u
+            25u
+             (concatLines [
+                "static member GetAwaiter:"
+                "   awaitable: 'Awaitable (requires member GetAwaiter )"
+                "           -> Awaiter<^Awaiter,'TResult> (requires :> ICriticalNotifyCompletion and member IsCompleted and member GetResult)"
+             ])
           verifySignature
             65u
             7u
@@ -442,7 +458,6 @@ let tooltipTests state =
             70u
             7u
             (concatLines
-
 #if NET8_0
               [ "active pattern ValueWithName: "
                 "   input: Expr"

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

@@ -69,4 +69,27 @@ let testActivePatternSignatureWithSubStringName (expr: Quotations.Expr) =
 
   match expr with
   | ValueWithName t -> t
-  | _ -> failwith "no value match"
+  | _ -> failwith "no value match"
+
+open System.Runtime.CompilerServices
+type IWSAMTest<'e> =
+    static abstract member Test : int -> 'e
+
+let testIWSAMTest<'e when IWSAMTest<'e>> () =
+  if 42 > 0 then Ok "Worlds Sane"
+  else Error ('e.Test 42)
+
+type Awaiter<'Awaiter, 'TResult
+    when 'Awaiter :> ICriticalNotifyCompletion
+    and 'Awaiter: (member get_IsCompleted: unit -> bool)
+    and 'Awaiter: (member GetResult: unit -> 'TResult)> = 'Awaiter
+
+type Awaitable<'Awaitable, 'Awaiter, 'TResult
+    when 'Awaitable: (member GetAwaiter: unit -> Awaiter<'Awaiter, 'TResult>)> = 'Awaitable
+
+type Awaitable =
+  static member inline GetAwaiter<'Awaitable, 'Awaiter, 'TResult
+      when Awaitable<'Awaitable, 'Awaiter, 'TResult>>
+      (awaitable: 'Awaitable)
+      =
+      awaitable.GetAwaiter()