Fixed bug that results in a false negative when solving a type variable that involves an invariant context. (#8051)

packages/pyright-internal/src/analyzer/constraintSolver.ts

@@ -516,6 +516,31 @@ export function assignTypeToTypeVar(
             }
         }
 
+        // If this is an invariant context, make sure the narrow type bound
+        // isn't too wide.
+        if (isInvariant && newNarrowTypeBound) {
+            if (
+                !evaluator.assignType(
+                    adjSrcType,
+                    newNarrowTypeBound,
+                    diag?.createAddendum(),
+                    /* destTypeVarContext */ undefined,
+                    /* srcTypeVarContext */ undefined,
+                    AssignTypeFlags.IgnoreTypeVarScope,
+                    recursionCount
+                )
+            ) {
+                if (diag && diagAddendum) {
+                    diag.addMessage(
+                        LocAddendum.typeAssignmentMismatch().format(
+                            evaluator.printSrcDestTypes(newNarrowTypeBound, adjSrcType)
+                        )
+                    );
+                }
+                return false;
+            }
+        }
+
         // Make sure we don't exceed the wide type bound.
         if (curWideTypeBound && newNarrowTypeBound) {
             if (!isTypeSame(curWideTypeBound, newNarrowTypeBound, {}, recursionCount)) {

packages/pyright-internal/src/tests/samples/namedTuple7.py

@@ -13,7 +13,6 @@ class NT1(NamedTuple, Generic[_T1]):
     c: list[_T1]
 
 
-reveal_type(NT1(3, 4, ["hi"]), expected_text="NT1[int | str]")
 reveal_type(NT1(3, 4, []), expected_text="NT1[int]")
 reveal_type(NT1(3.4, 4, [1, 2]), expected_text="NT1[float]")
 reveal_type(NT1(3.4, 4, [2j]), expected_text="NT1[complex]")

packages/pyright-internal/src/tests/samples/solver35.py

@@ -0,0 +1,20 @@
+# This sample tests the case where the constraint solver is asked to
+# solve a TypeVar that is in an invariant context.
+
+from typing import TypeVar
+
+T1 = TypeVar("T1")
+T2 = TypeVar("T2")
+
+
+def func1(v1: T1, v2: T2, v1_list: list[T1], v2_list: list[T2]): ...
+
+
+def func2(v1: int, v2: str, v1_list: list[int], v2_list: list[str]):
+    func1(v1, v2, v1_list, v2_list)
+
+    # This should generate an error because the last two arguments are swapped.
+    func1(v2, v1, v1_list, v2_list)
+
+    # This should generate an error because the last two arguments are swapped.
+    func1(v1_list=v1_list, v2_list=v2_list, v1=v2, v2=v1)

packages/pyright-internal/src/tests/typeEvaluator2.test.ts

@@ -765,6 +765,12 @@ test('Solver34', () => {
     TestUtils.validateResults(analysisResults, 1);
 });
 
+test('Solver35', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['solver35.py']);
+
+    TestUtils.validateResults(analysisResults, 4);
+});
+
 test('SolverScoring1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['solverScoring1.py']);