Mikhail Arkhipov (MikhailArkhipov) · Apr 17, 2019 · Mar 1, 2019 · Mar 1, 2019 · Mar 5, 2019 · Mar 5, 2019
diff --git a/src/Analysis/Ast/Impl/Analyzer/Evaluation/ExpressionEval.Collections.cs b/src/Analysis/Ast/Impl/Analyzer/Evaluation/ExpressionEval.Collections.cs
@@ -139,8 +139,8 @@ internal void ProcessComprehension(Comprehension node) {
                 var value = GetValueFromExpression(cfor.List);
                 if (value != null) {
                     switch (cfor.Left) {
-                        case NameExpression nex when value is IPythonCollection coll:
-                            DeclareVariable(nex.Name, coll.GetIterator().Next, VariableSource.Declaration, nex);
+                        case NameExpression nex when value is IPythonCollection c1:
+                            DeclareVariable(nex.Name, c1.GetIterator().Next, VariableSource.Declaration, nex);
                             break;
                         case NameExpression nex:
                             DeclareVariable(nex.Name, UnknownType, VariableSource.Declaration, nex);
@@ -156,6 +156,12 @@ internal void ProcessComprehension(Comprehension node) {
                                 DeclareVariable(item.Name, UnknownType, VariableSource.Declaration, item);
                             }
                             break;
+                        case TupleExpression tex when value is IPythonCollection c2 && tex.Items.Count > 0:
+                            var iter = c2.GetIterator();
+                            foreach (var item in tex.Items.OfType<NameExpression>().Where(x => !string.IsNullOrEmpty(x.Name))) {
+                                DeclareVariable(item.Name, iter.Next, VariableSource.Declaration, item);
+                            }
+                            break;
                     }
                 }
             }

diff --git a/src/Analysis/Ast/Impl/Linting/UndefinedVariables/ComprehensionWalker.cs b/src/Analysis/Ast/Impl/Linting/UndefinedVariables/ComprehensionWalker.cs
@@ -58,7 +58,7 @@ public override bool Walk(DictionaryComprehension node) {
             foreach (var iter in node.Iterators) {
                 iter?.Walk(ew);
             }
-            return true;
+            return false;
         }
 
         private NameCollectorWalker CollectNames(Comprehension c) {

diff --git a/src/Analysis/Ast/Test/LintUndefinedVarsTests.cs b/src/Analysis/Ast/Test/LintUndefinedVarsTests.cs
@@ -561,6 +561,17 @@ public async Task NoLeakFromComprehension() {
             d[0].SourceSpan.Should().Be(2, 33, 2, 34);
         }
 
+        [TestMethod, Priority(0)]
+        public async Task NestedDictComprehension() {
+            const string code = @"
+dmap = {}
+sizes = {}
+x = {srv:sum([sizes[d] for d in dbs]) for srv, dbs in dmap.items()}
+";
+            var d = await LintAsync(code);
+            d.Should().BeEmpty();
+        }
+
         private async Task<IReadOnlyList<DiagnosticsEntry>> LintAsync(string code, InterpreterConfiguration configuration = null) {
             var analysis = await GetAnalysisAsync(code, configuration ?? PythonVersions.LatestAvailable3X);
             var a = Services.GetService<IPythonAnalyzer>();