Some errors are missing after type checking a file

[auduchinok]

Repro steps

I found this issue in the Paket solution and good example file to reproduce is Program.fs in Paket project. (The links point to particular commit I had checked out.)
In many cases type checking results don't return errors when I randomly change identifiers in the file and expect them to become unresolved. Also there's no "type cannot be inferred" errors for expressions with these identifiers later in the code.
For example change processCommand identifier somehow (in the Program.fs) in its let binding or in any of usages in the end of the file.

Expected behavior

Worked fine in 6.0.2 and 9.0.1, the expected errors were shown.

Actual behavior

No errors at all in some cases.

[nightroman]

I also noticed that in FCS 10.0.1 some errors/warnings are not stable. Here is an extreme example:

#I @"some\missing\folder" // warning FS0211, missing
open System.Windows.Forms

let form = Form (Text = "Test Form") // warning FS0760 IDisposable
let button1 = Button (Text = "Test Button") // ditto

button1.Click.Add(fun args -> async1 label1 "bar bar bar") // error FS0039, not defined
button2.Click.Add(fun args -> async1 label1 "") // error FS0039, not defined

let x = Choice1Of2 42
match x with // warning FS0025 incomplete pattern
| Choice1Of2 x -> ()

let x = seq { // mark all to end but virtual space // error FS0789: invalid expression
    // mark first column
    // mark first column
    } // mark all from head

let test () =
if true // warning FS0058: incorrect indentation + error FS0589: incomplete conditional
    if true then // error FS0010: unexpected keyword
    let x = 42 // warning FS0058: incorrect indentation
    printfn "%s" x // warning FS0058: incorrect indentation

In 9.0.1 and before it should get 18 issues (some of them commented). In 10.0.1 sometimes it gets 11 issues, some issues in the middle are not reported. If I start to edit the file (just adding/removing empty lines) then sometimes it shows 18 expected issues, sometimes not.

[nightroman]

With the above script I was able to reproduce the problem with Ionide-fsharp
2.23.0 which uses FCS 10.0.3. It was a bit tricky. I had to switch between
two opened scripts in order to see the problem. Namely, on opening 14 issues
are found (see the problem pane Ctrl+Shift+M). Then on switching between
scripts, at some point only 7 issues are found. The picture is similar to
what I see in my scenario, some issues in the middle are missing.
Then after adding some empty lines to the script, 14 issues are found.

[dsyme]

@auduchinok @nightroman Can I confirm that this is when using an editing tools like Ionide? Which is in turn using FsAutoComplete? And that the likely culprit is ParseAndCheckFileInProject? Thanks

[auduchinok]

@dsyme I didn't use FsAutoComplete.
I made separate calls to ParseFileInProject and CheckFileInProject and worked with the results.
The project options were taken from ProjectCracker and I added some missing references to assemblies there.

[nightroman]

@dsyme In FSharpFar I do not use FsAutoComplete as such (to be precise, I borrowed some pieces for code completion, not checking). Yes, I use ParseAndCheckFileInProject. In the above scenario I get options by GetProjectOptionsFromScript.

In other words, I noticed the problem in my application first. I mentioned Ionide-fsharp because it started to have the similar issue on switching to FCS 10.0.3. My application started to have it on switching to 10.0.1.

[dsyme]

@nightroman @auduchinok I know the cause of the bug - we need to integrate fixes - currently preparing that

[dsyme]

This should be fixed in soon-to-be-release 11.0.1. The build is on appveyor now, you can grab the nuget packages when you're done https://ci.appveyor.com/project/fsgit/fsharp-compiler-service/build/11.0.1

[dsyme]

11.0.1 pushed, will appear in the catalog soon. Please help FsAutoComplete and Ionide upgrade to this too, it's important

[nightroman]

@dsyme Thank you. The problem seems to be fixed. Unfortunately, a new issue #706 was introduced and I cannot upgrade. The application uses the console UI (Far Manager, the orthodox console based file manager) and unwanted console output makes it unusable. I probably know some workarounds but I hope that Console.WriteLine in service.fs is just a mistake to be fixed soon.

[dsyme]

Fixed in 11.0.2, now released