From b623cb03891caa4838a56cb68d451f6904858a12 Mon Sep 17 00:00:00 2001
From: Eric Traut <erictr@microsoft.com>
Date: Sat, 15 Feb 2020 00:59:00 -0700
Subject: [PATCH] Fixed bug in type evaluator where it not properly handling
 properties within protocol classes.

---
 server/src/analyzer/typeEvaluator.ts  | 26 +++++++++++++++++
 server/src/tests/checker.test.ts      |  6 ++++
 server/src/tests/samples/protocol3.py | 41 +++++++++++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 server/src/tests/samples/protocol3.py

diff --git a/server/src/analyzer/typeEvaluator.ts b/server/src/analyzer/typeEvaluator.ts
index 8542c05352ca..8a1d3205ad7c 100644
--- a/server/src/analyzer/typeEvaluator.ts
+++ b/server/src/analyzer/typeEvaluator.ts
@@ -9033,6 +9033,32 @@ export function createTypeEvaluator(importLookup: ImportLookup): TypeEvaluator {
             return typesAreConsistent;
         }
 
+        // Handle property classes. They are special because each property
+        // class has a different source ID, so they wouldn't otherwise match.
+        // We need to see if the return types of the properties match.
+        if (ClassType.isPropertyClass(destType) && ClassType.isPropertyClass(srcType)) {
+            let typesAreConsistent = true;
+
+            const fgetDest = destType.details.fields.get('fget');
+            const fgetSrc = srcType.details.fields.get('fget');
+            if (fgetDest && fgetSrc) {
+                const fgetDestType = getDeclaredTypeOfSymbol(fgetDest);
+                const fgetSrcType = getDeclaredTypeOfSymbol(fgetSrc);
+                if (fgetDestType && fgetSrcType &&
+                            fgetDestType.category === TypeCategory.Function &&
+                            fgetSrcType.category === TypeCategory.Function) {
+
+                    const fgetDestReturnType = getFunctionEffectiveReturnType(fgetDestType);
+                    const fgetSrcReturnType = getFunctionEffectiveReturnType(fgetSrcType);
+                    if (!canAssignType(fgetDestReturnType, fgetSrcReturnType, diag)) {
+                        typesAreConsistent = false;
+                    }
+                }
+            }
+
+            return typesAreConsistent;
+        }
+
         // Special-case conversion for the "numeric tower".
         if (ClassType.isBuiltIn(destType, 'float')) {
             if (ClassType.isBuiltIn(srcType, 'int')) {
diff --git a/server/src/tests/checker.test.ts b/server/src/tests/checker.test.ts
index e56f5183cd54..ed42cf5191d9 100644
--- a/server/src/tests/checker.test.ts
+++ b/server/src/tests/checker.test.ts
@@ -882,6 +882,12 @@ test('Protocol2', () => {
     validateResults(analysisResults, 0);
 });
 
+test('Protocol3', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['protocol3.py']);
+
+    validateResults(analysisResults, 1);
+});
+
 test('TypedDict1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['typedDict1.py']);
 
diff --git a/server/src/tests/samples/protocol3.py b/server/src/tests/samples/protocol3.py
new file mode 100644
index 000000000000..01512a590b9a
--- /dev/null
+++ b/server/src/tests/samples/protocol3.py
@@ -0,0 +1,41 @@
+# This sample tests the assignment of protocols that
+# include property declarations.
+
+from typing import Protocol
+
+class Foo1(Protocol):
+    @property
+    def batch_shape(self) -> int:
+        return 0
+
+
+class MockFoo1:
+    def __init__(self, batch_shape: int):
+        self._batch_shape = batch_shape
+
+    @property
+    def batch_shape(self) -> int:
+        return self._batch_shape
+
+# This should not generate an error.
+d: Foo1 = MockFoo1(batch_shape=1)
+
+
+class Foo2(Protocol):
+    @property
+    def batch_shape(self) -> int:
+        return 0
+
+
+class MockFoo2:
+    def __init__(self, batch_shape: int):
+        self._batch_shape = batch_shape
+
+    @property
+    def batch_shape(self) -> float:
+        return self._batch_shape
+
+# This should generate an error because the
+# type of the batch_shape property is not compatible.
+e: Foo2 = MockFoo2(batch_shape=1)
+