Language server stops working after adding a new file

[anpaz]

Describe the bug

The language server randomly crashes while working on a Q# project in VS Code. When it does, it will not restart until VS Code re-opened and closed.

To Reproduce

Create a new Q# project. This particular one had a couple of not very big files (a couple of operations each). As I was working in VS Code I would get this Exception:

[Error - 11:11:46 PM] 
=============================
Microsoft.Quantum.QsCompiler.QsCompilerException: error while running queued task
NullReferenceException: Object reference not set to an instance of an object.
Stack trace: 
at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.PushChange(TextDocumentContentChangeEvent change, Boolean& publishDiagnostics) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 999
at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.ReplaceFileContent(String text) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 1053
at Microsoft.Quantum.QsCompiler.CompilationBuilder.CompilationUnitManager.<>c__DisplayClass18_0.<AddOrUpdateSourceFileAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\CompilationUnitManager.cs:line 275
at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56

at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
at Microsoft.Quantum.QsCompiler.CompilationBuilder.ProcessingQueue.<>c__DisplayClass4_0.<ProcessingTaskAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ProcessingQueue.cs:line 48
=============================

System information

• VS Code: 1.50.1
• Extension: 0.13.20102604
• OS: Mac OSX Catalina
• .NET Core: 3..403

[anpaz]

A little more information: looks like the server is actually not crashing, but every key entered generates the same information so everything stops working (auto-complete, code actions, hovering, etc). Saving a file doesn't fix the problem.

I am able to reproduce the same problem in Windows too. These are my steps:

• Create new Q# library project, open in VS Code.
• Open the Library.qs file to get the Q# extension started.
• Once ready, add a new .qs file, open the file.
• Add a namespace, an operation and start editing the operation, something like this:

namespace foo {
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Canon;

    // ...
    operation Bar(target : Qubit) : Unit
    is Adj + Ctl {
        // ...
        let =
    }

}

by the time I start writting let = I start seeing the exceptions in the output window.

[bamarsha]

Could you post the full log from the "Q# Language Extension" output? When I try to reproduce this, I noticed this happens:

[Info  - 14:53:14] workspace folder: c:\Users\samarsha\Desktop\Library
Discovered Q# project 'c:\Users\samarsha\Desktop\Library\Library.csproj'.
Loading project 'c:\Users\samarsha\Desktop\Library\Library.csproj'.
Done loading project 'c:\Users\samarsha\Desktop\Library\Library.csproj'
Discovered Q# project 'C:\Users\samarsha\AppData\Local\Temp\qsharp\c_x2f__x2f_Users_x2f_samarsha_x2f_Desktop_x2f_Library\generated.csproj'.
Loading project 'C:\Users\samarsha\AppData\Local\Temp\qsharp\c_x2f__x2f_Users_x2f_samarsha_x2f_Desktop_x2f_Library\generated.csproj'.
The file c:\Users\samarsha\Desktop\Library\Library.qs has been associated with the compilation unit C:\Users\samarsha\AppData\Local\Temp\qsharp\c_x2f__x2f_Users_x2f_samarsha_x2f_Desktop_x2f_Library\generated.csproj.
Done loading project 'C:\Users\samarsha\AppData\Local\Temp\qsharp\c_x2f__x2f_Users_x2f_samarsha_x2f_Desktop_x2f_Library\generated.csproj'
Discovered Q# project 'c:\Users\samarsha\Desktop\Library\Library.csproj'.
Loading project 'c:\Users\samarsha\Desktop\Library\Library.csproj'.
The file c:\Users\samarsha\Desktop\Library\Foo.qs has been associated with the compilation unit c:\Users\samarsha\Desktop\Library\Library.csproj.
Done loading project 'c:\Users\samarsha\Desktop\Library\Library.csproj'

which could be causing issues, because the language server should not be generating a temporary Q# project for a file that is already part of an existing Q# project. After this, I get some NullReferenceExceptions as well, but they're different from the one you're getting:

Microsoft.Quantum.QsCompiler.QsCompilerException: error while running queued task
QsCompilerException: error during scope tracking update
NullReferenceException: Object reference not set to an instance of an object.
Stack trace: 
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.DequeueUnprocessedChanges(Int32& lineNr, String& textToInsert) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 924
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.ScopeTracking.UpdateScopeTacking(FileContentManager file, TextDocumentContentChangeEvent change) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ScopeTracking.cs:line 733
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.<>c__DisplayClass68_0.<Update>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 944
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56

Stack trace: 
   at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.Update(TextDocumentContentChangeEvent change) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 945
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.PushChange(TextDocumentContentChangeEvent change, Boolean& publishDiagnostics) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 1035
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.CompilationUnitManager.<>c__DisplayClass20_0.<SourceFileDidChangeAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\CompilationUnitManager.cs:line 327
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56

   at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.ProcessingQueue.<>c__DisplayClass4_0.<ProcessingTaskAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ProcessingQueue.cs:line 42

[bamarsha]

Also, if you close VS Code and re-open the library you created earlier, does the problem still happen? Or does it only happen if you create a new project and file and open them in the same session?

[anpaz]

Here is all the logs up to the first couple of errors (let me know if you need more, but there is an stack trace for every key I stroke afterwards):

[Info  - 11:06:45 AM] workspace folder: c:\Repos\Temp\ls
Discovered Q# project 'c:\Repos\Temp\ls\ls.csproj'.
Loading project 'c:\Repos\Temp\ls\ls.csproj'.
Done loading project 'c:\Repos\Temp\ls\ls.csproj'
Discovered Q# project 'C:\Users\anpaz\AppData\Local\Temp\qsharp\c_x2f__x2f_Repos_x2f_Temp_x2f_ls\generated.csproj'.
Loading project 'C:\Users\anpaz\AppData\Local\Temp\qsharp\c_x2f__x2f_Repos_x2f_Temp_x2f_ls\generated.csproj'.
The file c:\Repos\Temp\ls\Library.qs has been associated with the compilation unit C:\Users\anpaz\AppData\Local\Temp\qsharp\c_x2f__x2f_Repos_x2f_Temp_x2f_ls\generated.csproj.
Done loading project 'C:\Users\anpaz\AppData\Local\Temp\qsharp\c_x2f__x2f_Repos_x2f_Temp_x2f_ls\generated.csproj'
Discovered Q# project 'c:\Repos\Temp\ls\ls.csproj'.
Loading project 'c:\Repos\Temp\ls\ls.csproj'.
The file c:\Repos\Temp\ls\bar.qs has been associated with the compilation unit c:\Repos\Temp\ls\ls.csproj.
Done loading project 'c:\Repos\Temp\ls\ls.csproj'
[Error - 11:09:32 AM] 
=============================
Microsoft.Quantum.QsCompiler.QsCompilerException: error while running queued task
QsCompilerException: error during scope tracking update
ArgumentOutOfRangeException: Specified argument was out of the range of valid values. (Parameter 'startChar')
Stack trace: 
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.Utils.GetChangedText(String lineText, Int32 startChar, Int32 endChar, String insert) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\Utils.cs:line 118
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.DequeueUnprocessedChanges(Int32& lineNr, String& textToInsert) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 924
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.ScopeTracking.UpdateScopeTacking(FileContentManager file, TextDocumentContentChangeEvent change) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ScopeTracking.cs:line 733
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.<>c__DisplayClass68_0.<Update>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 944
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 54

Stack trace: 
   at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.Update(TextDocumentContentChangeEvent change) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 945
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.PushChange(TextDocumentContentChangeEvent change, Boolean& publishDiagnostics) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 1035
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.CompilationUnitManager.<>c__DisplayClass20_0.<SourceFileDidChangeAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\CompilationUnitManager.cs:line 327
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 54

   at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.ProcessingQueue.<>c__DisplayClass4_0.<ProcessingTaskAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ProcessingQueue.cs:line 42
=============================

[Error - 11:09:38 AM] 
=============================
Microsoft.Quantum.QsCompiler.QsCompilerException: error while running queued task
InvalidOperationException: Collection was modified after the enumerator was instantiated.
Stack trace: 
   at System.Collections.Generic.Queue`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.Any[TSource](IEnumerable`1 source)
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.FileContentManager.PushChange(TextDocumentContentChangeEvent change, Boolean& publishDiagnostics) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\FileContentManager.cs:line 1001
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.CompilationUnitManager.<>c__DisplayClass20_0.<SourceFileDidChangeAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\CompilationUnitManager.cs:line 327
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56

   at Microsoft.Quantum.QsCompiler.QsCompilerError.Raise(String message, Exception innerException) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 27
   at Microsoft.Quantum.QsCompiler.QsCompilerError.RaiseOnFailure(Action action, String header) in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\DataStructures\ErrorHandling.fs:line 56
   at Microsoft.Quantum.QsCompiler.CompilationBuilder.ProcessingQueue.<>c__DisplayClass4_0.<ProcessingTaskAsync>b__0() in D:\a\1\s\submodules\qsharp-compiler\src\QsCompiler\CompilationManager\ProcessingQueue.cs:line 48
=============================