Fix signature help in CEs and use better heuristics (dotnet#10835) (dotnet#10847)

Author: cartermp

Completion/SignatureHelp.fs

@@ -226,24 +226,10 @@ type internal FSharpSignatureHelpProvider
             documentationBuilder: IDocumentationBuilder,
             sourceText: SourceText,
             caretPosition: int,
+            adjustedColumnInSource: int,
             filePath: string
         ) =
         asyncMaybe {
-            // Backtrack to find a non-whitespace character to get curried arg infos (if present) and a symbol to inspect.
-            let adjustedColumnInSource =
-                let rec loop s c =
-                    if String.IsNullOrWhiteSpace(s.ToString()) then
-                        loop (sourceText.GetSubText(c - 1)) (c - 1)
-                    else
-                        c
-                let startText =
-                    if caretPosition = sourceText.Length then
-                        sourceText.GetSubText(caretPosition)
-                    else
-                        sourceText.GetSubText(TextSpan(caretPosition, 1))
-                
-                loop startText caretPosition
-
             let textLine = sourceText.Lines.GetLineFromPosition(adjustedColumnInSource)
             let textLinePos = sourceText.Lines.GetLinePosition(adjustedColumnInSource)
             let pos = mkPos (Line.fromZ textLinePos.Line) textLinePos.Character
@@ -465,19 +451,28 @@ type internal FSharpSignatureHelpProvider
             let perfOptions = document.FSharpOptions.LanguageServicePerformance
 
             let! parseResults, _, checkFileResults = checker.ParseAndCheckDocument(filePath, textVersionHash, sourceText, options, perfOptions, userOpName = userOpName)
-            match parseResults.FindNoteworthyParamInfoLocations(Pos.fromZ caretLinePos.Line caretLineColumn) with
-            | Some paramInfoLocations ->
-                return!
-                    FSharpSignatureHelpProvider.ProvideMethodsAsyncAux(
-                        caretLinePos,
-                        caretLineColumn,
-                        paramInfoLocations,
-                        checkFileResults,
-                        documentationBuilder,
-                        sourceText,
-                        caretPosition,
-                        triggerTypedChar)
-            | None ->
+
+            let adjustedColumnInSource =
+                let rec loop s c =
+                    if String.IsNullOrWhiteSpace(s.ToString()) then
+                        loop (sourceText.GetSubText(c - 1)) (c - 1)
+                    else
+                        c
+                let startText =
+                    if caretPosition = sourceText.Length then
+                        sourceText.GetSubText(caretPosition)
+                    else
+                        sourceText.GetSubText(TextSpan(caretPosition, 1))
+                
+                loop startText caretPosition
+
+            let adjustedColumnString = sourceText.GetSubText(TextSpan(adjustedColumnInSource, 1)).ToString()
+
+            match triggerTypedChar with
+            // Generally ' ' indicates a function application, but it's also used commonly after a comma in a method call.
+            // This means that the adjusted position relative to the caret could be a ',' or a ')' or '>',
+            // which would mean we're already inside of a method call - not a function argument. So we bail if that's the case.
+            | Some ' ' when adjustedColumnString <> "," && adjustedColumnString <> ")" && adjustedColumnString <> ">" ->
                 return!
                     FSharpSignatureHelpProvider.ProvideParametersAsyncAux(
                         parseResults,
@@ -487,7 +482,20 @@ type internal FSharpSignatureHelpProvider
                         documentationBuilder,
                         sourceText,
                         caretPosition,
+                        adjustedColumnInSource,
                         filePath)
+            | _ ->
+                let! paramInfoLocations = parseResults.FindNoteworthyParamInfoLocations(Pos.fromZ caretLinePos.Line caretLineColumn)
+                return!
+                    FSharpSignatureHelpProvider.ProvideMethodsAsyncAux(
+                        caretLinePos,
+                        caretLineColumn,
+                        paramInfoLocations,
+                        checkFileResults,
+                        documentationBuilder,
+                        sourceText,
+                        caretPosition,
+                        triggerTypedChar)
         }
 
     interface IFSharpSignatureHelpProvider with