Implemented type analysis support for comparison chaining.

server/src/analyzer/expressionEvaluator.ts

@@ -2750,7 +2750,20 @@ export class ExpressionEvaluator {
     }
 
     private _getTypeFromBinaryExpression(node: BinaryExpressionNode): TypeResult {
-        let leftType = this.getType(node.leftExpression);
+        let leftExpression = node.leftExpression;
+
+        // If this is a comparison and the left expression is also a comparison,
+        // we need to change the behavior to accommodate python's "chained
+        // comparisons" feature.
+        if (comparisonOperatorMap[node.operator]) {
+            if (node.leftExpression.nodeType === ParseNodeType.BinaryOperation &&
+                    comparisonOperatorMap[node.leftExpression.operator]) {
+
+                leftExpression = node.leftExpression.rightExpression;
+            }
+        }
+
+        let leftType = this.getType(leftExpression);
 
         // Is this an AND operator? If so, we can assume that the
         // rightExpression won't be evaluated at runtime unless the
@@ -2813,7 +2826,6 @@ export class ExpressionEvaluator {
         };
 
         let type: Type | undefined;
-
         const leftType = this.getType(node.leftExpression);
         const rightType = this.getType(node.rightExpression);
 

server/src/tests/samples/operators2.py

@@ -0,0 +1,23 @@
+# This sample tests the type checker's handling of chained
+# comparison operators.
+
+from datetime import datetime
+
+def requires_bool(val: bool):
+    pass
+
+date1 = datetime.now()
+date2 = datetime.now()
+date3 = datetime.now()
+
+foo1 = date1 < date2 <= date3
+requires_bool(foo1)
+
+int1 = 3
+foo2 = 2 < int1 < 5
+requires_bool(foo2)
+
+# This should generate an error because
+# int and datetime cannot be compared.
+foo3 = date1 < date2 < 3
+

server/src/tests/typeAnalyzer.test.ts

@@ -267,6 +267,12 @@ test('Operators1', () => {
     validateResults(analysisResults, 3);
 });
 
+test('Operators2', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['operators2.py']);
+
+    validateResults(analysisResults, 1);
+});
+
 test('Optional1', () => {
     const configOptions = new ConfigOptions('.');