Offer F# declarations to the Copilot chat "#" mention picker

docs/release-notes/.VisualStudio/18.vNext.md

@@ -2,6 +2,7 @@
 
 * Code-fixes for FS3888 (compiler-semantic attribute on the `.fs` but not the `.fsi`): copy the attribute into the `.fsi`, or remove it from the `.fs`. ([Issue #19560](https://github.com/dotnet/fsharp/issues/19560), [PR #19880](https://github.com/dotnet/fsharp/pull/19880))
 * Expand `<inheritdoc/>` in IDE tooltips, completion, and signature help, inheriting XML documentation from base classes, interfaces, overridden members, and constructors. ([Issue #19175](https://github.com/dotnet/fsharp/issues/19175), [PR #19188](https://github.com/dotnet/fsharp/pull/19188))
+* F# types, modules, members and values now appear in the GitHub Copilot Chat `#` mention picker, and attach their declaration source as context. ([PR #20409](https://github.com/dotnet/fsharp/pull/20409))
 
 ### Fixed
 

eng/Packages.props

@@ -64,6 +64,9 @@
          ComponentModelHost would otherwise stay at 17.x; that 17.x/18.x split makes S/IComponentModel ambiguous
          (CS0433). Pin to the SDK 18.9.496 version so those types resolve to a single assembly. -->
     <PackageVersion Include="Microsoft.VisualStudio.ComponentModelHost" Version="18.9.453" />
+    <!-- Copilot chat contracts. Kept on the 18.9.x wave so its MessagePack and editor dependencies match the pins
+         above. Compile-only: at runtime the VS-installed contract assembly wins through Copilot's binding redirect. -->
+    <PackageVersion Include="Microsoft.VisualStudio.Copilot" Version="18.9.918" />
     <PackageVersion Include="Microsoft.VisualStudio.Designer.Interfaces" Version="18.9.438" />
     <PackageVersion Include="Microsoft.VisualStudio.Editor" Version="$(VisualStudioEditorPackagesVersion)" />
     <PackageVersion Include="Microsoft.VisualStudio.Extensibility.Build" Version="17.13.39620" />

vsintegration/src/FSharp.Editor/Common/CancellableTasks.fs

@@ -1130,6 +1130,13 @@ module CancellableTasks =
                 return! allTask
             }
 
+        /// Runs the work over the items with at most maxDegreeOfParallelism of them in flight.
+        let forEachThrottled maxDegreeOfParallelism (work: 'T -> CancellableTask<unit>) (items: 'T seq) =
+            cancellableTask {
+                let! ct = getCancellationToken ()
+                return! Task.parallelDoLimit maxDegreeOfParallelism ct (items |> Seq.map work)
+            }
+
         let inline whenAllTasks (tasks: CancellableTask seq) =
             cancellableTask {
                 let! ct = getCancellationToken ()

vsintegration/src/FSharp.Editor/Common/Constants.fs

@@ -43,6 +43,11 @@ module internal FSharpConstants =
     /// "F# Language Service"
     let FSharpLanguageServiceCallbackName = "F# Language Service"
 
+    [<Literal>]
+    /// Brokered service offering F# declarations to the Copilot chat "#" mention picker.
+    let copilotSymbolProviderName =
+        "Microsoft.VisualStudio.FSharp.CopilotSymbolContextProvider"
+
     [<Literal>]
     /// "FSharp"
     let FSharpLanguageLongName = "FSharp"