From 3aea365b5ab0469f12f8058d1445e88e0bf6e502 Mon Sep 17 00:00:00 2001
From: Eric Traut <erictr@microsoft.com>
Date: Mon, 27 Dec 2021 17:00:18 -0700
Subject: [PATCH] Fixed regression in type alias handling.

---
 .../src/analyzer/typeEvaluator.ts                | 13 +++++++++++--
 .../src/tests/samples/typeAlias11.py             | 16 ++++++++++++++++
 .../src/tests/typeEvaluator3.test.ts             |  6 ++++++
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 packages/pyright-internal/src/tests/samples/typeAlias11.py

diff --git a/packages/pyright-internal/src/analyzer/typeEvaluator.ts b/packages/pyright-internal/src/analyzer/typeEvaluator.ts
index 790390eaa..f78c9c2dd 100644
--- a/packages/pyright-internal/src/analyzer/typeEvaluator.ts
+++ b/packages/pyright-internal/src/analyzer/typeEvaluator.ts
@@ -6099,7 +6099,7 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                 typeArgs.push(getTypeArgTypeResult(item, index));
             });
 
-            // Mark the node's type so it isn't reevaluated later.
+            // Set the node's type so it isn't reevaluated later.
             setTypeForNode(node.items[0].valueExpression);
         } else {
             node.items.forEach((arg, index) => {
@@ -6153,7 +6153,8 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                 node,
             };
 
-            writeTypeCache(node, UnknownType.create(), adjustedFlags, /* isIncomplete */ false);
+            // Set the node's type so it isn't reevaluated later.
+            setTypeForNode(node);
         } else {
             typeResult = getTypeOfExpression(node, /* expectedType */ undefined, adjustedFlags);
 
@@ -12974,12 +12975,19 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
             if (!rightHandType) {
                 // Determine whether there is a declared type.
                 const declaredType = getDeclaredTypeForExpression(node.leftExpression, { method: 'set' });
+
                 let flags: EvaluatorFlags = EvaluatorFlags.None;
                 if (fileInfo.isStubFile) {
                     // An assignment of ellipsis means "Any" within a type stub file.
                     flags |= EvaluatorFlags.ConvertEllipsisToUnknown;
                 }
 
+                if (node.rightExpression.nodeType === ParseNodeType.Name) {
+                    // Don't specialize a generic class on assignment (e.g. "x = list") because 
+                    // we may want to later specialize it (e.g. "x[int]").
+                    flags |= EvaluatorFlags.DoNotSpecialize;
+                }
+
                 let typeAliasNameNode: NameNode | undefined;
                 let isSpeculativeTypeAlias = false;
 
@@ -12989,6 +12997,7 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                         EvaluatorFlags.EvaluateStringLiteralAsType |
                         EvaluatorFlags.ParamSpecDisallowed |
                         EvaluatorFlags.TypeVarTupleDisallowed;
+                    flags &= ~EvaluatorFlags.DoNotSpecialize;
 
                     typeAliasNameNode = (node.leftExpression as TypeAnnotationNode).valueExpression as NameNode;
                 } else if (node.leftExpression.nodeType === ParseNodeType.Name) {
diff --git a/packages/pyright-internal/src/tests/samples/typeAlias11.py b/packages/pyright-internal/src/tests/samples/typeAlias11.py
new file mode 100644
index 000000000..ee6206351
--- /dev/null
+++ b/packages/pyright-internal/src/tests/samples/typeAlias11.py
@@ -0,0 +1,16 @@
+# This sample tests the simple aliasing of a generic class with no
+# type arguments.
+
+from typing import Generic, Literal, TypeVar
+
+
+_T = TypeVar("_T")
+
+
+class ClassA(Generic[_T]):
+    def __init__(self, x: _T):
+        pass
+
+
+A = ClassA
+t1: Literal["ClassA[int]"] = reveal_type(A(3))
diff --git a/packages/pyright-internal/src/tests/typeEvaluator3.test.ts b/packages/pyright-internal/src/tests/typeEvaluator3.test.ts
index 90d4e89f6..34b65a90c 100644
--- a/packages/pyright-internal/src/tests/typeEvaluator3.test.ts
+++ b/packages/pyright-internal/src/tests/typeEvaluator3.test.ts
@@ -372,6 +372,12 @@ test('TypeAlias10', () => {
     TestUtils.validateResults(analysisResults, 4);
 });
 
+test('TypeAlias11', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['typeAlias11.py']);
+
+    TestUtils.validateResults(analysisResults, 0);
+});
+
 test('RecursiveTypeAlias1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['recursiveTypeAlias1.py']);