Merge branch 'master' of https://github.com/microsoft/python-language-server into stubnav

Author: Mikhail Arkhipov

CONTRIBUTING.md

@@ -4,15 +4,15 @@
 
 ### Prerequisites
 
-1. .NET Core 2.2 SDK
+1. .NET Core 3.1 SDK
    - [Windows](https://www.microsoft.com/net/learn/get-started/windows)
    - [Mac OS](https://www.microsoft.com/net/learn/get-started/macos)
    - [Linux](https://www.microsoft.com/net/learn/get-started/linux/rhel)
 2. C# Extension to [VS Code](https://code.visualstudio.com) (all platforms)
 3. Python 2.7
-4. Python 3.6
+4. Python 3.6+
 
-*Alternative:* [Visual Studio 2017 or 2019](https://www.visualstudio.com/downloads/) (Windows only) with .NET Core and C# Workloads. Community Edition is free and is fully functional.
+*Alternative:* [Visual Studio 2019](https://www.visualstudio.com/downloads/) (Windows only) with .NET Core and C# Workloads. Community Edition is free and is fully functional.
 
 ### Setup
 
@@ -54,7 +54,7 @@ On Windows you can also attach from Visual Studio (Debug | Attach To Process).
 ### Unit Tests
 To run unit tests, do one of the following:
 - Run the Unit Tests in the [VS Code Python Extension](https://github.com/Microsoft/vscode-python) project via *Launch Language Server Tests*.
-- On Windows: open the `PLS.sln` solution in Visual Studio 2017 or 2019 and run tests from the Test Explorer.
+- On Windows: open the `PLS.sln` solution in Visual Studio 2019 and run tests from the Test Explorer.
 - Run `dotnet test` from Terminal in the `src` directory, or in a specific directory like `src/Analysis/Ast/Test` to test a specific suite.
 - Install C# extension and .NET Core Test Explorer for VS Code, open src folder in VS Code and run tests.
 

src/Analysis/Ast/Impl/Analyzer/Evaluation/ExpressionEval.Scopes.cs

@@ -21,7 +21,6 @@
 using Microsoft.Python.Analysis.Values;
 using Microsoft.Python.Core;
 using Microsoft.Python.Core.Disposables;
-using Microsoft.Python.Core.Text;
 using Microsoft.Python.Parsing.Ast;
 
 namespace Microsoft.Python.Analysis.Analyzer.Evaluation {
@@ -55,12 +54,12 @@ public void DeclareVariable(string name, IMember value, VariableSource source, L
             if (member != null && !overwrite) {
                 return;
             }
-            
+
             if (source == VariableSource.Import && value is IVariable v) {
                 CurrentScope.LinkVariable(name, v, location);
                 return;
             }
-            
+
             if (member != null) {
                 if (!value.IsUnknown()) {
                     CurrentScope.DeclareVariable(name, value, source, location);
@@ -193,10 +192,17 @@ public void Dispose() {
                 // them better.
                 // TODO: figure out threading/locking for the Open/Close pairs.
                 // Debug.Assert(_eval._openScopes.Count > 0, "Attempt to close global scope");
-                if (_eval._openScopes.Count > 0) {
-                    _eval._openScopes.Pop();
+                try {
+                    if (_eval._openScopes.Count > 0) {
+                        _eval._openScopes.Pop();
+                    }
+                    _eval.CurrentScope = _eval._openScopes.Count == 0 ? _eval.GlobalScope : _eval._openScopes.Peek();
+                } catch (InvalidOperationException) {
+                    // Per comment above this can happen occasionally.
+                    // The catch is tactical fix to prevent crashes since complete handling of open/close
+                    // in threaded cases would be much larger change.
+                    _eval.Log?.Log(TraceEventType.Verbose, "Error: Mismatched open/close in scope tracker - scope stack is empty on Dispose()");
                 }
-                _eval.CurrentScope = _eval._openScopes.Count == 0 ? _eval.GlobalScope : _eval._openScopes.Peek();
             }
         }
     }