Changed inference logic for exception groups to more closely match the runtime. If a non-base exception is targeted, the inferred type is now ExceptionGroup rather than BaseExceptionGroup. This addresses #9466. (#9467)

Author: erictraut

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

@@ -19446,6 +19446,7 @@ export function createTypeEvaluator(
 
         const exceptionTypeResult = getTypeOfExpression(node.d.typeExpr!);
         const exceptionTypes = exceptionTypeResult.type;
+        let includesBaseException = false;
 
         function getExceptionType(exceptionType: Type, errorNode: ExpressionNode) {
             exceptionType = makeTopLevelTypeVarsConcrete(exceptionType);
@@ -19455,6 +19456,9 @@ export function createTypeEvaluator(
             }
 
             if (isInstantiableClass(exceptionType)) {
+                if (ClassType.isBuiltIn(exceptionType, 'BaseException')) {
+                    includesBaseException = true;
+                }
                 return ClassType.cloneAsInstance(exceptionType);
             }
 
@@ -19492,9 +19496,13 @@ export function createTypeEvaluator(
             return getExceptionType(subType, node.d.typeExpr!);
         });
 
-        // If this is an except group, wrap the exception type in an BaseExceptionGroup.
+        // If this is an except group, wrap the exception type in an ExceptionGroup
+        // or BaseExceptionGroup depending on whether the target exception is
+        // a BaseException.
         if (node.d.isExceptGroup) {
-            targetType = getBuiltInObject(node, 'BaseExceptionGroup', [targetType]);
+            targetType = getBuiltInObject(node, includesBaseException ? 'BaseExceptionGroup' : 'ExceptionGroup', [
+                targetType,
+            ]);
         }
 
         if (node.d.name) {

packages/pyright-internal/src/tests/samples/exceptionGroup1.py

@@ -9,7 +9,7 @@ def func1():
 
     # This should generate an error if using Python 3.10 or earlier.
     except* ValueError as e:
-        reveal_type(e, expected_text="BaseExceptionGroup[ValueError]")
+        reveal_type(e, expected_text="ExceptionGroup[ValueError]")
         pass
 
     # This should generate an error if using Python 3.10 or earlier.
@@ -105,3 +105,19 @@ def inner():
             # return is not allowed in an except* block.
             return
 
+
+
+def func8():
+
+    try:
+        pass
+
+    # This should generate an error if using Python 3.10 or earlier.
+    except* (ValueError, FloatingPointError) as e:
+        reveal_type(e, expected_text="ExceptionGroup[ValueError | FloatingPointError]")
+        pass
+
+    # This should generate an error if using Python 3.10 or earlier.
+    except* BaseException as e:
+        reveal_type(e, expected_text="BaseExceptionGroup[BaseException]")
+        pass

packages/pyright-internal/src/tests/typeEvaluator7.test.ts

@@ -971,7 +971,7 @@ test('exceptionGroup1', () => {
 
     configOptions.defaultPythonVersion = pythonVersion3_10;
     const analysisResults1 = TestUtils.typeAnalyzeSampleFiles(['exceptionGroup1.py'], configOptions);
-    TestUtils.validateResults(analysisResults1, 28);
+    TestUtils.validateResults(analysisResults1, 34);
 
     configOptions.defaultPythonVersion = pythonVersion3_11;
     const analysisResults2 = TestUtils.typeAnalyzeSampleFiles(['exceptionGroup1.py'], configOptions);