Suppress hover/symbol resolution for wildcard _ patterns inside member _.…

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -1,5 +1,6 @@
 ### Fixed
 
+* Suppress hover/symbol resolution for wildcard `_` patterns inside `member _.…` bodies that incorrectly showed `val _: T` tooltip. ([PR #19760](https://github.com/dotnet/fsharp/pull/19760))
 * Honor `--nowarn` and `--warnaserror` for warnings emitted during command-line option parsing ([Issue #19576](https://github.com/dotnet/fsharp/issues/19576), [PR #19776](https://github.com/dotnet/fsharp/pull/19776))
 * Fix `[<return: X>]` prefix attributes being silently dropped on class members, and fix false-positive `AllowMultiple=false` errors when `[<X>]` and `[<return: X>]` are applied to the same binding. ([Issue #17904](https://github.com/dotnet/fsharp/issues/17904), [Issue #19020](https://github.com/dotnet/fsharp/issues/19020), [PR #19738](https://github.com/dotnet/fsharp/pull/19738))
 * Fix attributes on return type of unparenthesized tuple methods being silently dropped from IL. ([Issue #462](https://github.com/dotnet/fsharp/issues/462), [PR #19714](https://github.com/dotnet/fsharp/pull/19714))

src/Compiler/Service/FSharpCheckerResults.fs

@@ -1631,11 +1631,18 @@ type internal TypeCheckInfo
                         | None -> ValueNone
                     | _ -> ValueNone
 
+            // Wildcard _ should not resolve to the member's synthetic self-identifier via fallback.
+            let isDiscardIdentifier =
+                match residueOpt, origLongIdentOpt with
+                | None, Some [ "_" ] -> true
+                | _ -> false
+
             match nameResItems with
             | NameResResult.Cancel(denv, m) -> Some([], denv, m)
             | NameResResult.Members(FilterRelevantItems getItem exactMatchResidueOpt (items, denv, m)) ->
                 // lookup based on name resolution results successful
                 Some(items |> List.map (CompletionItem (getType ()) ValueNone), denv, m)
+            | _ when isDiscardIdentifier -> None
             | _ ->
                 match origLongIdentOpt with
                 | None -> None

tests/FSharp.Compiler.Service.Tests/TooltipTests.fs

@@ -399,6 +399,9 @@ let assertNameTagInTooltip expectedTag expectedName (tooltip: ToolTipText) =
     let desc = tags |> Array.map (fun t -> sprintf "(%A, %s)" t.Tag t.Text) |> String.concat ", "
     Assert.True(found, sprintf "Expected tag %A with text '%s' in tooltip, but found: %s" expectedTag expectedName desc)
 
+let assertToolTipIsEmpty (ToolTipText(items)) =
+    Assert.Empty items
+
 let normalize (s: string) = s.Replace("\r\n", "\n").Replace("\n\n", "\n")
 
 [<Fact>]
@@ -594,6 +597,43 @@ let y = normaliz{caret}e' 5
     |> assertAndGetSingleToolTipText
     |> Assert.shouldBeEquivalentTo "val normalize': x: int -> int"
 
+[<Fact>]
+let ``Wildcard lambda parameter inside member with underscore instance identifier has no tooltip`` () =
+    Checker.getTooltip """
+type T () =
+    member _.M () =
+        fun _{caret} -> ()
+"""
+    |> assertToolTipIsEmpty
+
+[<Fact>]
+let ``Wildcard let binding inside member with underscore instance identifier has no tooltip`` () =
+    Checker.getTooltip """
+type T () =
+    member _.N () =
+        let _{caret} = () in ()
+"""
+    |> assertToolTipIsEmpty
+
+[<Fact>]
+let ``Wildcard match pattern inside member with underscore instance identifier has no tooltip`` () =
+    Checker.getTooltip """
+type T () =
+    member _.M (x: int) =
+        match x with
+        | _{caret} -> ()
+"""
+    |> assertToolTipIsEmpty
+
+[<Fact>]
+let ``Named self-identifier is not affected by wildcard discard fix`` () =
+    Checker.getTooltip """
+type T () =
+    member thi{caret}s.M () = ()
+"""
+    |> assertAndGetSingleToolTipText
+    |> Assert.shouldContain "T"
+
 // https://github.com/dotnet/fsharp/issues/13194
 [<Fact>]
 let ``Sig file XML doc fallback works for member whose name contains a single quote`` () =