Improve linting of LHS expressions

src/Analysis/Ast/Impl/Linting/UndefinedVariables/ExpressionWalker.cs

@@ -17,7 +17,6 @@
 using System.Linq;
 using Microsoft.Python.Analysis.Analyzer;
 using Microsoft.Python.Analysis.Types;
-using Microsoft.Python.Core;
 using Microsoft.Python.Core.Text;
 using Microsoft.Python.Parsing.Ast;
 using Microsoft.Python.Parsing.Extensions;

src/Analysis/Ast/Impl/Linting/UndefinedVariables/UndefinedVariablesWalker.cs

@@ -26,7 +26,6 @@
 namespace Microsoft.Python.Analysis.Linting.UndefinedVariables {
     internal sealed class UndefinedVariablesWalker : LinterWalker {
         private readonly List<DiagnosticsEntry> _diagnostics = new List<DiagnosticsEntry>();
-        private bool _suppressDiagnostics;
 
         public UndefinedVariablesWalker(IDocumentAnalysis analysis, IServiceContainer services)
             : base(analysis, services) { }
@@ -53,11 +52,9 @@ public override bool Walk(SuiteStatement node) {
                         augs.Right?.Walk(new ExpressionWalker(this));
                         break;
                     case AssignmentStatement asst:
-                        _suppressDiagnostics = true;
-                        foreach (var lhs in asst.Left ?? Enumerable.Empty<Expression>()) {
+                        foreach (var lhs in asst.Left.MaybeEnumerate().Where(x => !(x is NameExpression))) {
                             lhs?.Walk(new ExpressionWalker(this));
                         }
-                        _suppressDiagnostics = false;
                         asst.Right?.Walk(new ExpressionWalker(this));
                         break;
                     default:
@@ -73,12 +70,10 @@ public void ReportUndefinedVariable(NameExpression node) {
             ReportUndefinedVariable(node.Name, eval.GetLocation(node).Span);
         }
 
-        public void ReportUndefinedVariable(string name, SourceSpan span) {
-            if (!_suppressDiagnostics) {
-                _diagnostics.Add(new DiagnosticsEntry(
-                    Resources.UndefinedVariable.FormatInvariant(name),
-                    span, ErrorCodes.UndefinedVariable, Severity.Warning, DiagnosticSource.Linter));
-            }
+        private void ReportUndefinedVariable(string name, SourceSpan span) {
+            _diagnostics.Add(new DiagnosticsEntry(
+                Resources.UndefinedVariable.FormatInvariant(name),
+                span, ErrorCodes.UndefinedVariable, Severity.Warning, DiagnosticSource.Linter));
         }
 
         private void HandleGlobal(GlobalStatement node) {

src/Analysis/Ast/Test/LintNoSelfArgumentTests.cs

@@ -19,7 +19,6 @@
 using Microsoft.Python.Analysis.Diagnostics;
 using Microsoft.Python.Analysis.Tests.FluentAssertions;
 using Microsoft.Python.Core;
-using Microsoft.Python.Parsing.Tests;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using TestUtilities;
 

src/Analysis/Ast/Test/LintReturnInInitTests.cs

@@ -18,7 +18,6 @@
 using FluentAssertions;
 using Microsoft.Python.Analysis.Tests.FluentAssertions;
 using Microsoft.Python.Parsing;
-using Microsoft.Python.Parsing.Tests;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using TestUtilities;
 

src/Analysis/Ast/Test/LintUndefinedVarsTests.cs

@@ -832,6 +832,18 @@ public async Task AugmentedAssignToUndefined() {
             d[0].SourceSpan.Should().Be(2, 1, 2, 2);
         }
 
+        [TestMethod, Priority(0)]
+        public async Task UndefinedInInit() {
+            const string code = @"
+class TestIt():
+    def __init__(self):
+        slf.y = 6
+";
+            var d = await LintAsync(code);
+            d.Should().HaveCount(1);
+            d[0].ErrorCode.Should().Be(ErrorCodes.UndefinedVariable);
+            d[0].SourceSpan.Should().Be(4, 9, 4, 12);
+        }
 
         private async Task<IReadOnlyList<DiagnosticsEntry>> LintAsync(string code, InterpreterConfiguration configuration = null) {
             var analysis = await GetAnalysisAsync(code, configuration ?? PythonVersions.LatestAvailable3X);