Better breakpoint support when clicking (#2815)

* Better breakpoint support when clicking - fixes #2814

* Do not break on empty lines

* No need to parse if we are standing on empty lines

src/fsharp/vs/ServiceUntypedParse.fs

@@ -351,12 +351,24 @@ type FSharpParseFileResults(errors : FSharpErrorInfo[], input : Ast.ParsedInput
             (fun () -> 
                 let locations = findBreakPoints()
                 
-                match locations |> List.filter (fun m -> rangeContainsPos m pos) with
-                | [] ->
-                    match locations |> List.filter (fun m -> rangeBeforePos m pos |> not) with
-                    | [] -> Seq.tryHead locations
-                    | locationsAfterPos -> Seq.tryHead locationsAfterPos
-                | coveringLocations -> Seq.tryLast coveringLocations)
+                if pos.Column = 0 then
+                    // we have a breakpoint that was set with mouse at line start
+                    match locations |> List.filter (fun m -> m.StartLine = m.EndLine && pos.Line = m.StartLine) with
+                    | [] ->
+                        match locations |> List.filter (fun m -> rangeContainsPos m pos) with
+                        | [] ->
+                            match locations |> List.filter (fun m -> rangeBeforePos m pos |> not) with
+                            | [] -> Seq.tryHead locations
+                            | locationsAfterPos -> Seq.tryHead locationsAfterPos
+                        | coveringLocations -> Seq.tryLast coveringLocations
+                    | locationsOnSameLine -> Seq.tryHead locationsOnSameLine
+                else
+                    match locations |> List.filter (fun m -> rangeContainsPos m pos) with
+                    | [] ->
+                        match locations |> List.filter (fun m -> rangeBeforePos m pos |> not) with
+                        | [] -> Seq.tryHead locations
+                        | locationsAfterPos -> Seq.tryHead locationsAfterPos
+                    | coveringLocations -> Seq.tryLast coveringLocations)
             (fun _msg -> None)
             
     /// When these files appear or disappear the configuration for the current project is invalidated.

vsintegration/src/FSharp.Editor/Debugging/BreakpointResolutionService.fs

@@ -2,6 +2,7 @@
 
 namespace Microsoft.VisualStudio.FSharp.Editor
 
+open System
 open System.Composition
 open System.Collections.Generic
 open System.Threading
@@ -32,11 +33,16 @@ type internal FSharpBreakpointResolutionService
             // cross-project checking in multi-project solutions). FCS will not respond to other 
             // requests unless this task is cancelled. We need to check that this task is cancelled in a timely way by the
             // Roslyn UI machinery.
-            let! parseResults = checker.ParseFileInProject(fileName, sourceText.ToString(), options)
             let textLinePos = sourceText.Lines.GetLinePosition(textSpan.Start)
-            let textLineColumn = textLinePos.Character
-            let fcsTextLineNumber = Line.fromZ textLinePos.Line // Roslyn line numbers are zero-based, FSharp.Compiler.Service line numbers are 1-based
-            return parseResults.ValidateBreakpointLocation(mkPos fcsTextLineNumber textLineColumn)
+            let textInLine = sourceText.GetSubText(sourceText.Lines.[textLinePos.Line].Span).ToString()
+
+            if String.IsNullOrWhiteSpace textInLine then
+                return None
+            else
+                let textLineColumn = textLinePos.Character
+                let fcsTextLineNumber = Line.fromZ textLinePos.Line // Roslyn line numbers are zero-based, FSharp.Compiler.Service line numbers are 1-based
+                let! parseResults = checker.ParseFileInProject(fileName, sourceText.ToString(), options)
+                return parseResults.ValidateBreakpointLocation(mkPos fcsTextLineNumber textLineColumn)
         }
 
     interface IBreakpointResolutionService with
@@ -50,6 +56,6 @@ type internal FSharpBreakpointResolutionService
             |> Async.map Option.toObj 
             |> RoslynHelpers.StartAsyncAsTask cancellationToken
             
-        // FSROSLYNTODO: enable placing breakpoints by when user suplies fully-qualified function names
+        // FSROSLYNTODO: enable placing breakpoints by when user supplies fully-qualified function names
         member this.ResolveBreakpointsAsync(_, _, _): Task<IEnumerable<BreakpointResolutionResult>> =
             Task.FromResult(Enumerable.Empty<BreakpointResolutionResult>())
\ No newline at end of file