fire event when a value is bound at the root of a script evaluation (#7919)

* fire event when a value is bound at the root of a script evaluation

* simplify event notifying bound values in interactive

src/fsharp/FSharp.Compiler.Private.Scripting/FSharpScript.fs

@@ -38,6 +38,8 @@ type FSharpScript(?captureInput: bool, ?captureOutput: bool, ?additionalArgs: st
 
     member __.AssemblyReferenceAdded = fsi.AssemblyReferenceAdded
 
+    member __.ValueBound = fsi.ValueBound
+
     member __.ProvideInput = stdin.ProvideInput
 
     member __.OutputProduced = outputProduced.Publish

src/fsharp/fsi/fsi.fs

@@ -950,6 +950,7 @@ type internal FsiDynamicCompiler
     let assemblyName = "FSI-ASSEMBLY"
 
     let assemblyReferenceAddedEvent = Control.Event<string>()
+    let valueBoundEvent = Control.Event<_>()
 
     let mutable fragmentId = 0
     let mutable prevIt : ValRef option = None
@@ -1155,6 +1156,10 @@ type internal FsiDynamicCompiler
                             if v.CompiledName = "it" then
                                 itValue <- fsiValueOpt
 
+                            match fsiValueOpt with
+                            | Some fsiValue -> valueBoundEvent.Trigger(fsiValue.ReflectionValue, fsiValue.ReflectionType, v.CompiledName)
+                            | None -> ()
+
                             let symbol = FSharpSymbol.Create(cenv, v.Item)
                             let symbolUse = FSharpSymbolUse(tcGlobals, newState.tcState.TcEnvFromImpls.DisplayEnv, symbol, ItemOccurence.Binding, v.DeclarationLocation)
                             fsi.TriggerEvaluation (fsiValueOpt, symbolUse, decl)
@@ -1331,6 +1336,8 @@ type internal FsiDynamicCompiler
 
     member __.AssemblyReferenceAdded = assemblyReferenceAddedEvent.Publish
 
+    member __.ValueBound = valueBoundEvent.Publish
+
 //----------------------------------------------------------------------------
 // ctrl-c handling
 //----------------------------------------------------------------------------
@@ -2222,7 +2229,6 @@ type internal FsiInteractionProcessor
         let fsiInteractiveChecker = FsiInteractiveChecker(legacyReferenceResolver, checker, tcConfig, istate.tcGlobals, istate.tcImports, istate.tcState)
         fsiInteractiveChecker.ParseAndCheckInteraction(ctok, SourceText.ofString text)
 
-
 //----------------------------------------------------------------------------
 // Server mode:
 //----------------------------------------------------------------------------
@@ -2630,6 +2636,9 @@ type FsiEvaluationSession (fsi: FsiEvaluationSessionHostConfig, argv:string[], i
 
     /// Event fires every time an assembly reference is added to the execution environment, e.g., via `#r`.
     member __.AssemblyReferenceAdded = fsiDynamicCompiler.AssemblyReferenceAdded
+
+    /// Event fires when a root-level value is bound to an identifier, e.g., via `let x = ...`.
+    member __.ValueBound = fsiDynamicCompiler.ValueBound
  
     /// Performs these steps:
     ///    - Load the dummy interaction, if any

src/fsharp/fsi/fsi.fsi

@@ -237,6 +237,9 @@ type FsiEvaluationSession =
     /// Event fires every time an assembly reference is added to the execution environment, e.g., via `#r`.
     member AssemblyReferenceAdded : IEvent<string>
 
+    /// Event fires when a root-level value is bound to an identifier, e.g., via `let x = ...`.
+    member ValueBound : IEvent<obj * System.Type * string>
+
     /// Load the dummy interaction, load the initial files, and,
     /// if interacting, start the background thread to read the standard input.
     ///

tests/FSharp.Compiler.Private.Scripting.UnitTests/FSharpScriptTests.fs

@@ -122,3 +122,49 @@ type InteractiveTests() =
         Assert.True(wasCancelled)
         Assert.LessOrEqual(sw.ElapsedMilliseconds, sleepTime)
         Assert.AreEqual(None, result)
+
+    [<Test>]
+    member _.``Values bound at the root trigger an event``() =
+        let mutable foundX = false
+        let mutable foundY = false
+        let mutable foundCount = 0
+        use script = new FSharpScript()
+        script.ValueBound
+        |> Event.add (fun (value, typ, name) ->
+            foundX <- foundX || (name = "x" && typ = typeof<int> && value :?> int = 1)
+            foundY <- foundY || (name = "y" && typ = typeof<int> && value :?> int = 2)
+            foundCount <- foundCount + 1)
+        let code = @"
+let x = 1
+let y = 2
+"
+        script.Eval(code) |> ignoreValue
+        Assert.True(foundX)
+        Assert.True(foundY)
+        Assert.AreEqual(2, foundCount)
+
+    [<Test>]
+    member _.``Values re-bound trigger an event``() =
+        let mutable foundXCount = 0
+        use script = new FSharpScript()
+        script.ValueBound
+        |> Event.add (fun (_value, typ, name) ->
+            if name = "x" && typ = typeof<int> then foundXCount <- foundXCount + 1)
+        script.Eval("let x = 1") |> ignoreValue
+        script.Eval("let x = 2") |> ignoreValue
+        Assert.AreEqual(2, foundXCount)
+
+    [<Test>]
+    member _.``Nested let bindings don't trigger event``() =
+        let mutable foundInner = false
+        use script = new FSharpScript()
+        script.ValueBound
+        |> Event.add (fun (_value, _typ, name) ->
+            foundInner <- foundInner || name = "inner")
+        let code = @"
+let x =
+    let inner = 1
+    ()
+"
+        script.Eval(code) |> ignoreValue
+        Assert.False(foundInner)