Fix repr() for recursive type aliases

JelleZijlstra · JelleZijlstra · commit 27a8a4cc34d2 · 2023-04-25T17:34:59.000-06:00
diff --git a/Lib/test/test_type_aliases.py b/Lib/test/test_type_aliases.py
@@ -127,3 +127,11 @@ def __repr__(self):
 
         type Generic[T, *Ts, **P] = int
         self.assertEqual(repr(Generic), "<type alias Generic[T, *Ts, **P]: int>")
+
+    def test_recursive_repr(self):
+        type Recursive = Recursive
+        self.assertEqual(repr(Recursive), "<type alias Recursive: ...>")
+
+        type X = list[Y]
+        type Y = list[X]
+        self.assertEqual(repr(X), "<type alias X: list[<type alias Y: list[...]>]>")
diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
@@ -1249,6 +1249,14 @@ typealias_evaluate(typealiasobject *ta)
 static PyObject *
 typealias_repr(PyObject *self)
 {
+    Py_ssize_t res = Py_ReprEnter(self);
+    if (res > 0) {
+        return PyUnicode_FromString("...");
+    }
+    else if (res < 0) {
+        return NULL;
+    }
+
     typealiasobject *ta = (typealiasobject *)self;
     PyObject *value_repr = NULL;
     PyObject *value = typealias_evaluate(ta);
@@ -1271,6 +1279,7 @@ typealias_repr(PyObject *self)
     }
     if (value_repr == NULL) {
         // PyUnicode_FromString failed
+        Py_ReprLeave(self);
         return NULL;
     }
     PyObject *result = NULL;
@@ -1321,6 +1330,7 @@ typealias_repr(PyObject *self)
         result = PyUnicode_FromFormat("<type alias %s: %U>", ta->name, value_repr);
     }
 error:
+    Py_ReprLeave(self);
     Py_DECREF(value_repr);
     return result;
 }

Original file line number	Diff line number	Diff line change
`@@ -1249,6 +1249,14 @@ typealias_evaluate(typealiasobject *ta)`
`1249`	`1249`	`static PyObject *`
`1250`	`1250`	`typealias_repr(PyObject *self)`
`1251`	`1251`	`{`
	`1252`	`+ Py_ssize_t res = Py_ReprEnter(self);`
	`1253`	`+ if (res > 0) {`
	`1254`	`+ return PyUnicode_FromString("...");`
	`1255`	`+ }`
	`1256`	`+ else if (res < 0) {`
	`1257`	`+ return NULL;`
	`1258`	`+ }`
	`1259`	`+`
`1252`	`1260`	`typealiasobject ta = (typealiasobject )self;`
`1253`	`1261`	`PyObject *value_repr = NULL;`
`1254`	`1262`	`PyObject *value = typealias_evaluate(ta);`
`@@ -1271,6 +1279,7 @@ typealias_repr(PyObject *self)`
`1271`	`1279`	`}`
`1272`	`1280`	`if (value_repr == NULL) {`
`1273`	`1281`	`// PyUnicode_FromString failed`
	`1282`	`+ Py_ReprLeave(self);`
`1274`	`1283`	`return NULL;`
`1275`	`1284`	`}`
`1276`	`1285`	`PyObject *result = NULL;`
`@@ -1321,6 +1330,7 @@ typealias_repr(PyObject *self)`
`1321`	`1330`	`result = PyUnicode_FromFormat("<type alias %s: %U>", ta->name, value_repr);`
`1322`	`1331`	`}`
`1323`	`1332`	`error:`
	`1333`	`+ Py_ReprLeave(self);`
`1324`	`1334`	`Py_DECREF(value_repr);`
`1325`	`1335`	`return result;`
`1326`	`1336`	`}`