gh-116126: Implement PEP 696 (#116129)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

5 files changed, 286 insertions, 53 deletions

diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 60b4626..cc7734e 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -203,6 +203,7 @@ void _PyAST_Fini(PyInterpreterState *interp)
     Py_CLEAR(state->conversion);
     Py_CLEAR(state->ctx);
     Py_CLEAR(state->decorator_list);
+    Py_CLEAR(state->default_value);
     Py_CLEAR(state->defaults);
     Py_CLEAR(state->elt);
     Py_CLEAR(state->elts);
@@ -311,6 +312,7 @@ static int init_identifiers(struct ast_state *state)
     if ((state->conversion = PyUnicode_InternFromString("conversion")) == NULL) return -1;
     if ((state->ctx = PyUnicode_InternFromString("ctx")) == NULL) return -1;
     if ((state->decorator_list = PyUnicode_InternFromString("decorator_list")) == NULL) return -1;
+    if ((state->default_value = PyUnicode_InternFromString("default_value")) == NULL) return -1;
     if ((state->defaults = PyUnicode_InternFromString("defaults")) == NULL) return -1;
     if ((state->elt = PyUnicode_InternFromString("elt")) == NULL) return -1;
     if ((state->elts = PyUnicode_InternFromString("elts")) == NULL) return -1;
@@ -809,12 +811,15 @@ static PyObject* ast2obj_type_param(struct ast_state *state, struct validator
 static const char * const TypeVar_fields[]={
     "name",
     "bound",
+    "default_value",
 };
 static const char * const ParamSpec_fields[]={
     "name",
+    "default_value",
 };
 static const char * const TypeVarTuple_fields[]={
     "name",
+    "default_value",
 };
 
 
@@ -4913,6 +4918,22 @@ add_ast_annotations(struct ast_state *state)
             return 0;
         }
     }
+    {
+        PyObject *type = state->expr_type;
+        type = _Py_union_type_or(type, Py_None);
+        cond = type != NULL;
+        if (!cond) {
+            Py_DECREF(TypeVar_annotations);
+            return 0;
+        }
+        cond = PyDict_SetItemString(TypeVar_annotations, "default_value", type)
+                                    == 0;
+        Py_DECREF(type);
+        if (!cond) {
+            Py_DECREF(TypeVar_annotations);
+            return 0;
+        }
+    }
     cond = PyObject_SetAttrString(state->TypeVar_type, "_field_types",
                                   TypeVar_annotations) == 0;
     if (!cond) {
@@ -4938,6 +4959,22 @@ add_ast_annotations(struct ast_state *state)
             return 0;
         }
     }
+    {
+        PyObject *type = state->expr_type;
+        type = _Py_union_type_or(type, Py_None);
+        cond = type != NULL;
+        if (!cond) {
+            Py_DECREF(ParamSpec_annotations);
+            return 0;
+        }
+        cond = PyDict_SetItemString(ParamSpec_annotations, "default_value",
+                                    type) == 0;
+        Py_DECREF(type);
+        if (!cond) {
+            Py_DECREF(ParamSpec_annotations);
+            return 0;
+        }
+    }
     cond = PyObject_SetAttrString(state->ParamSpec_type, "_field_types",
                                   ParamSpec_annotations) == 0;
     if (!cond) {
@@ -4964,6 +5001,22 @@ add_ast_annotations(struct ast_state *state)
             return 0;
         }
     }
+    {
+        PyObject *type = state->expr_type;
+        type = _Py_union_type_or(type, Py_None);
+        cond = type != NULL;
+        if (!cond) {
+            Py_DECREF(TypeVarTuple_annotations);
+            return 0;
+        }
+        cond = PyDict_SetItemString(TypeVarTuple_annotations, "default_value",
+                                    type) == 0;
+        Py_DECREF(type);
+        if (!cond) {
+            Py_DECREF(TypeVarTuple_annotations);
+            return 0;
+        }
+    }
     cond = PyObject_SetAttrString(state->TypeVarTuple_type, "_field_types",
                                   TypeVarTuple_annotations) == 0;
     if (!cond) {
@@ -6243,28 +6296,37 @@ init_types(struct ast_state *state)
     if (!state->TypeIgnore_type) return -1;
     state->type_param_type = make_type(state, "type_param", state->AST_type,
                                        NULL, 0,
-        "type_param = TypeVar(identifier name, expr? bound)\n"
-        "           | ParamSpec(identifier name)\n"
-        "           | TypeVarTuple(identifier name)");
+        "type_param = TypeVar(identifier name, expr? bound, expr? default_value)\n"
+        "           | ParamSpec(identifier name, expr? default_value)\n"
+        "           | TypeVarTuple(identifier name, expr? default_value)");
     if (!state->type_param_type) return -1;
     if (add_attributes(state, state->type_param_type, type_param_attributes, 4)
         < 0) return -1;
     state->TypeVar_type = make_type(state, "TypeVar", state->type_param_type,
-                                    TypeVar_fields, 2,
-        "TypeVar(identifier name, expr? bound)");
+                                    TypeVar_fields, 3,
+        "TypeVar(identifier name, expr? bound, expr? default_value)");
     if (!state->TypeVar_type) return -1;
     if (PyObject_SetAttr(state->TypeVar_type, state->bound, Py_None) == -1)
         return -1;
+    if (PyObject_SetAttr(state->TypeVar_type, state->default_value, Py_None) ==
+        -1)
+        return -1;
     state->ParamSpec_type = make_type(state, "ParamSpec",
                                       state->type_param_type, ParamSpec_fields,
-                                      1,
-        "ParamSpec(identifier name)");
+                                      2,
+        "ParamSpec(identifier name, expr? default_value)");
     if (!state->ParamSpec_type) return -1;
+    if (PyObject_SetAttr(state->ParamSpec_type, state->default_value, Py_None)
+        == -1)
+        return -1;
     state->TypeVarTuple_type = make_type(state, "TypeVarTuple",
                                          state->type_param_type,
-                                         TypeVarTuple_fields, 1,
-        "TypeVarTuple(identifier name)");
+                                         TypeVarTuple_fields, 2,
+        "TypeVarTuple(identifier name, expr? default_value)");
     if (!state->TypeVarTuple_type) return -1;
+    if (PyObject_SetAttr(state->TypeVarTuple_type, state->default_value,
+        Py_None) == -1)
+        return -1;
 
     if (!add_ast_annotations(state)) {
         return -1;
@@ -8055,8 +8117,9 @@ _PyAST_TypeIgnore(int lineno, string tag, PyArena *arena)
 }
 
 type_param_ty
-_PyAST_TypeVar(identifier name, expr_ty bound, int lineno, int col_offset, int
-               end_lineno, int end_col_offset, PyArena *arena)
+_PyAST_TypeVar(identifier name, expr_ty bound, expr_ty default_value, int
+               lineno, int col_offset, int end_lineno, int end_col_offset,
+               PyArena *arena)
 {
     type_param_ty p;
     if (!name) {
@@ -8070,6 +8133,7 @@ _PyAST_TypeVar(identifier name, expr_ty bound, int lineno, int col_offset, int
     p->kind = TypeVar_kind;
     p->v.TypeVar.name = name;
     p->v.TypeVar.bound = bound;
+    p->v.TypeVar.default_value = default_value;
     p->lineno = lineno;
     p->col_offset = col_offset;
     p->end_lineno = end_lineno;
@@ -8078,8 +8142,8 @@ _PyAST_TypeVar(identifier name, expr_ty bound, int lineno, int col_offset, int
 }
 
 type_param_ty
-_PyAST_ParamSpec(identifier name, int lineno, int col_offset, int end_lineno,
-                 int end_col_offset, PyArena *arena)
+_PyAST_ParamSpec(identifier name, expr_ty default_value, int lineno, int
+                 col_offset, int end_lineno, int end_col_offset, PyArena *arena)
 {
     type_param_ty p;
     if (!name) {
@@ -8092,6 +8156,7 @@ _PyAST_ParamSpec(identifier name, int lineno, int col_offset, int end_lineno,
         return NULL;
     p->kind = ParamSpec_kind;
     p->v.ParamSpec.name = name;
+    p->v.ParamSpec.default_value = default_value;
     p->lineno = lineno;
     p->col_offset = col_offset;
     p->end_lineno = end_lineno;
@@ -8100,8 +8165,9 @@ _PyAST_ParamSpec(identifier name, int lineno, int col_offset, int end_lineno,
 }
 
 type_param_ty
-_PyAST_TypeVarTuple(identifier name, int lineno, int col_offset, int
-                    end_lineno, int end_col_offset, PyArena *arena)
+_PyAST_TypeVarTuple(identifier name, expr_ty default_value, int lineno, int
+                    col_offset, int end_lineno, int end_col_offset, PyArena
+                    *arena)
 {
     type_param_ty p;
     if (!name) {
@@ -8114,6 +8180,7 @@ _PyAST_TypeVarTuple(identifier name, int lineno, int col_offset, int
         return NULL;
     p->kind = TypeVarTuple_kind;
     p->v.TypeVarTuple.name = name;
+    p->v.TypeVarTuple.default_value = default_value;
     p->lineno = lineno;
     p->col_offset = col_offset;
     p->end_lineno = end_lineno;
@@ -10079,6 +10146,11 @@ ast2obj_type_param(struct ast_state *state, struct validator *vstate, void* _o)
         if (PyObject_SetAttr(result, state->bound, value) == -1)
             goto failed;
         Py_DECREF(value);
+        value = ast2obj_expr(state, vstate, o->v.TypeVar.default_value);
+        if (!value) goto failed;
+        if (PyObject_SetAttr(result, state->default_value, value) == -1)
+            goto failed;
+        Py_DECREF(value);
         break;
     case ParamSpec_kind:
         tp = (PyTypeObject *)state->ParamSpec_type;
@@ -10089,6 +10161,11 @@ ast2obj_type_param(struct ast_state *state, struct validator *vstate, void* _o)
         if (PyObject_SetAttr(result, state->name, value) == -1)
             goto failed;
         Py_DECREF(value);
+        value = ast2obj_expr(state, vstate, o->v.ParamSpec.default_value);
+        if (!value) goto failed;
+        if (PyObject_SetAttr(result, state->default_value, value) == -1)
+            goto failed;
+        Py_DECREF(value);
         break;
     case TypeVarTuple_kind:
         tp = (PyTypeObject *)state->TypeVarTuple_type;
@@ -10099,6 +10176,11 @@ ast2obj_type_param(struct ast_state *state, struct validator *vstate, void* _o)
         if (PyObject_SetAttr(result, state->name, value) == -1)
             goto failed;
         Py_DECREF(value);
+        value = ast2obj_expr(state, vstate, o->v.TypeVarTuple.default_value);
+        if (!value) goto failed;
+        if (PyObject_SetAttr(result, state->default_value, value) == -1)
+            goto failed;
+        Py_DECREF(value);
         break;
     }
     value = ast2obj_int(state, vstate, o->lineno);
@@ -16935,6 +17017,7 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
     if (isinstance) {
         identifier name;
         expr_ty bound;
+        expr_ty default_value;
 
         if (PyObject_GetOptionalAttr(obj, state->name, &tmp) < 0) {
             return -1;
@@ -16970,8 +17053,25 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
             if (res != 0) goto failed;
             Py_CLEAR(tmp);
         }
-        *out = _PyAST_TypeVar(name, bound, lineno, col_offset, end_lineno,
-                              end_col_offset, arena);
+        if (PyObject_GetOptionalAttr(obj, state->default_value, &tmp) < 0) {
+            return -1;
+        }
+        if (tmp == NULL || tmp == Py_None) {
+            Py_CLEAR(tmp);
+            default_value = NULL;
+        }
+        else {
+            int res;
+            if (_Py_EnterRecursiveCall(" while traversing 'TypeVar' node")) {
+                goto failed;
+            }
+            res = obj2ast_expr(state, tmp, &default_value, arena);
+            _Py_LeaveRecursiveCall();
+            if (res != 0) goto failed;
+            Py_CLEAR(tmp);
+        }
+        *out = _PyAST_TypeVar(name, bound, default_value, lineno, col_offset,
+                              end_lineno, end_col_offset, arena);
         if (*out == NULL) goto failed;
         return 0;
     }
@@ -16982,6 +17082,7 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
     }
     if (isinstance) {
         identifier name;
+        expr_ty default_value;
 
         if (PyObject_GetOptionalAttr(obj, state->name, &tmp) < 0) {
             return -1;
@@ -17000,8 +17101,25 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
             if (res != 0) goto failed;
             Py_CLEAR(tmp);
         }
-        *out = _PyAST_ParamSpec(name, lineno, col_offset, end_lineno,
-                                end_col_offset, arena);
+        if (PyObject_GetOptionalAttr(obj, state->default_value, &tmp) < 0) {
+            return -1;
+        }
+        if (tmp == NULL || tmp == Py_None) {
+            Py_CLEAR(tmp);
+            default_value = NULL;
+        }
+        else {
+            int res;
+            if (_Py_EnterRecursiveCall(" while traversing 'ParamSpec' node")) {
+                goto failed;
+            }
+            res = obj2ast_expr(state, tmp, &default_value, arena);
+            _Py_LeaveRecursiveCall();
+            if (res != 0) goto failed;
+            Py_CLEAR(tmp);
+        }
+        *out = _PyAST_ParamSpec(name, default_value, lineno, col_offset,
+                                end_lineno, end_col_offset, arena);
         if (*out == NULL) goto failed;
         return 0;
     }
@@ -17012,6 +17130,7 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
     }
     if (isinstance) {
         identifier name;
+        expr_ty default_value;
 
         if (PyObject_GetOptionalAttr(obj, state->name, &tmp) < 0) {
             return -1;
@@ -17030,8 +17149,25 @@ obj2ast_type_param(struct ast_state *state, PyObject* obj, type_param_ty* out,
             if (res != 0) goto failed;
             Py_CLEAR(tmp);
         }
-        *out = _PyAST_TypeVarTuple(name, lineno, col_offset, end_lineno,
-                                   end_col_offset, arena);
+        if (PyObject_GetOptionalAttr(obj, state->default_value, &tmp) < 0) {
+            return -1;
+        }
+        if (tmp == NULL || tmp == Py_None) {
+            Py_CLEAR(tmp);
+            default_value = NULL;
+        }
+        else {
+            int res;
+            if (_Py_EnterRecursiveCall(" while traversing 'TypeVarTuple' node")) {
+                goto failed;
+            }
+            res = obj2ast_expr(state, tmp, &default_value, arena);
+            _Py_LeaveRecursiveCall();
+            if (res != 0) goto failed;
+            Py_CLEAR(tmp);
+        }
+        *out = _PyAST_TypeVarTuple(name, default_value, lineno, col_offset,
+                                   end_lineno, end_col_offset, arena);
         if (*out == NULL) goto failed;
         return 0;
     }
diff --git a/Python/ast.c b/Python/ast.c
index 71b09d8..1d1a48e 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -1011,13 +1011,19 @@ validate_typeparam(struct validator *state, type_param_ty tp)
         case TypeVar_kind:
             ret = validate_name(tp->v.TypeVar.name) &&
                 (!tp->v.TypeVar.bound ||
-                 validate_expr(state, tp->v.TypeVar.bound, Load));
+                 validate_expr(state, tp->v.TypeVar.bound, Load)) &&
+                (!tp->v.TypeVar.default_value ||
+                 validate_expr(state, tp->v.TypeVar.default_value, Load));
             break;
         case ParamSpec_kind:
-            ret = validate_name(tp->v.ParamSpec.name);
+            ret = validate_name(tp->v.ParamSpec.name) &&
+                (!tp->v.ParamSpec.default_value ||
+                 validate_expr(state, tp->v.ParamSpec.default_value, Load));
             break;
         case TypeVarTuple_kind:
-            ret = validate_name(tp->v.TypeVarTuple.name);
+            ret = validate_name(tp->v.TypeVarTuple.name) &&
+                (!tp->v.TypeVarTuple.default_value ||
+                 validate_expr(state, tp->v.TypeVarTuple.default_value, Load));
             break;
     }
     return ret;
diff --git a/Python/compile.c b/Python/compile.c
index feedd98..ec47af1 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2117,12 +2117,43 @@ wrap_in_stopiteration_handler(struct compiler *c)
 }
 
 static int
+compiler_type_param_bound_or_default(struct compiler *c, expr_ty e,
+                                     identifier name, void *key,
+                                     bool allow_starred)
+{
+    if (compiler_enter_scope(c, name, COMPILER_SCOPE_TYPEPARAMS,
+                             key, e->lineno) == -1) {
+        return ERROR;
+    }
+    if (allow_starred && e->kind == Starred_kind) {
+        VISIT(c, expr, e->v.Starred.value);
+        ADDOP_I(c, LOC(e), UNPACK_SEQUENCE, (Py_ssize_t)1);
+    }
+    else {
+        VISIT(c, expr, e);
+    }
+    ADDOP_IN_SCOPE(c, LOC(e), RETURN_VALUE);
+    PyCodeObject *co = optimize_and_assemble(c, 1);
+    compiler_exit_scope(c);
+    if (co == NULL) {
+        return ERROR;
+    }
+    if (compiler_make_closure(c, LOC(e), co, 0) < 0) {
+        Py_DECREF(co);
+        return ERROR;
+    }
+    Py_DECREF(co);
+    return SUCCESS;
+}
+
+static int
 compiler_type_params(struct compiler *c, asdl_type_param_seq *type_params)
 {
     if (!type_params) {
         return SUCCESS;
     }
     Py_ssize_t n = asdl_seq_LEN(type_params);
+    bool seen_default = false;
 
     for (Py_ssize_t i = 0; i < n; i++) {
         type_param_ty typeparam = asdl_seq_GET(type_params, i);
@@ -2132,22 +2163,10 @@ compiler_type_params(struct compiler *c, asdl_type_param_seq *type_params)
             ADDOP_LOAD_CONST(c, loc, typeparam->v.TypeVar.name);
             if (typeparam->v.TypeVar.bound) {
                 expr_ty bound = typeparam->v.TypeVar.bound;
-                if (compiler_enter_scope(c, typeparam->v.TypeVar.name, COMPILER_SCOPE_TYPEPARAMS,
-                                        (void *)typeparam, bound->lineno) == -1) {
+                if (compiler_type_param_bound_or_default(c, bound, typeparam->v.TypeVar.name,
+                                                         (void *)typeparam, false) < 0) {
                     return ERROR;
                 }
-                VISIT_IN_SCOPE(c, expr, bound);
-                ADDOP_IN_SCOPE(c, loc, RETURN_VALUE);
-                PyCodeObject *co = optimize_and_assemble(c, 1);
-                compiler_exit_scope(c);
-                if (co == NULL) {
-                    return ERROR;
-                }
-                if (compiler_make_closure(c, loc, co, 0) < 0) {
-                    Py_DECREF(co);
-                    return ERROR;
-                }
-                Py_DECREF(co);
 
                 int intrinsic = bound->kind == Tuple_kind
                     ? INTRINSIC_TYPEVAR_WITH_CONSTRAINTS
@@ -2157,18 +2176,60 @@ compiler_type_params(struct compiler *c, asdl_type_param_seq *type_params)
             else {
                 ADDOP_I(c, loc, CALL_INTRINSIC_1, INTRINSIC_TYPEVAR);
             }
+            if (typeparam->v.TypeVar.default_value) {
+                seen_default = true;
+                expr_ty default_ = typeparam->v.TypeVar.default_value;
+                if (compiler_type_param_bound_or_default(c, default_, typeparam->v.TypeVar.name,
+                                                         (void *)((uintptr_t)typeparam + 1), false) < 0) {
+                    return ERROR;
+                }
+                ADDOP_I(c, loc, CALL_INTRINSIC_2, INTRINSIC_SET_TYPEPARAM_DEFAULT);
+            }
+            else if (seen_default) {
+                return compiler_error(c, loc, "non-default type parameter '%U' "
+                                      "follows default type parameter",
+                                      typeparam->v.TypeVar.name);
+            }
             ADDOP_I(c, loc, COPY, 1);
             RETURN_IF_ERROR(compiler_nameop(c, loc, typeparam->v.TypeVar.name, Store));
             break;
         case TypeVarTuple_kind:
             ADDOP_LOAD_CONST(c, loc, typeparam->v.TypeVarTuple.name);
             ADDOP_I(c, loc, CALL_INTRINSIC_1, INTRINSIC_TYPEVARTUPLE);
+            if (typeparam->v.TypeVarTuple.default_value) {
+                expr_ty default_ = typeparam->v.TypeVarTuple.default_value;
+                if (compiler_type_param_bound_or_default(c, default_, typeparam->v.TypeVarTuple.name,
+                                                         (void *)typeparam, true) < 0) {
+                    return ERROR;
+                }
+                ADDOP_I(c, loc, CALL_INTRINSIC_2, INTRINSIC_SET_TYPEPARAM_DEFAULT);
+                seen_default = true;
+            }
+            else if (seen_default) {
+                return compiler_error(c, loc, "non-default type parameter '%U' "
+                                      "follows default type parameter",
+                                      typeparam->v.TypeVarTuple.name);
+            }
             ADDOP_I(c, loc, COPY, 1);
             RETURN_IF_ERROR(compiler_nameop(c, loc, typeparam->v.TypeVarTuple.name, Store));
             break;
         case ParamSpec_kind:
             ADDOP_LOAD_CONST(c, loc, typeparam->v.ParamSpec.name);
             ADDOP_I(c, loc, CALL_INTRINSIC_1, INTRINSIC_PARAMSPEC);
+            if (typeparam->v.ParamSpec.default_value) {
+                expr_ty default_ = typeparam->v.ParamSpec.default_value;
+                if (compiler_type_param_bound_or_default(c, default_, typeparam->v.ParamSpec.name,
+                                                         (void *)typeparam, false) < 0) {
+                    return ERROR;
+                }
+                ADDOP_I(c, loc, CALL_INTRINSIC_2, INTRINSIC_SET_TYPEPARAM_DEFAULT);
+                seen_default = true;
+            }
+            else if (seen_default) {
+                return compiler_error(c, loc, "non-default type parameter '%U' "
+                                      "follows default type parameter",
+                                      typeparam->v.ParamSpec.name);
+            }
             ADDOP_I(c, loc, COPY, 1);
             RETURN_IF_ERROR(compiler_nameop(c, loc, typeparam->v.ParamSpec.name, Store));
             break;
diff --git a/Python/intrinsics.c b/Python/intrinsics.c
index d314697..5b10c3c 100644
--- a/Python/intrinsics.c
+++ b/Python/intrinsics.c
@@ -265,6 +265,7 @@ _PyIntrinsics_BinaryFunctions[] = {
     INTRINSIC_FUNC_ENTRY(INTRINSIC_TYPEVAR_WITH_BOUND, make_typevar_with_bound)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_TYPEVAR_WITH_CONSTRAINTS, make_typevar_with_constraints)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_FUNCTION_TYPE_PARAMS, _Py_set_function_type_params)
+    INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_TYPEPARAM_DEFAULT, _Py_set_typeparam_default)
 };
 
 #undef INTRINSIC_FUNC_ENTRY
diff --git a/Python/symtable.c b/Python/symtable.c
index eecd159..2ec21a2 100644
--- a/Python/symtable.c
+++ b/Python/symtable.c
@@ -2276,6 +2276,24 @@ symtable_visit_expr(struct symtable *st, expr_ty e)
 }
 
 static int
+symtable_visit_type_param_bound_or_default(struct symtable *st, expr_ty e, identifier name, void *key)
+{
+    if (e) {
+        int is_in_class = st->st_cur->ste_can_see_class_scope;
+        if (!symtable_enter_block(st, name, TypeVarBoundBlock, key, LOCATION(e)))
+            return 0;
+        st->st_cur->ste_can_see_class_scope = is_in_class;
+        if (is_in_class && !symtable_add_def(st, &_Py_ID(__classdict__), USE, LOCATION(e))) {
+            VISIT_QUIT(st, 0);
+        }
+        VISIT(st, expr, e);
+        if (!symtable_exit_block(st))
+            return 0;
+    }
+    return 1;
+}
+
+static int
 symtable_visit_type_param(struct symtable *st, type_param_ty tp)
 {
     if (++st->recursion_depth > st->recursion_limit) {
@@ -2287,28 +2305,39 @@ symtable_visit_type_param(struct symtable *st, type_param_ty tp)
     case TypeVar_kind:
         if (!symtable_add_def(st, tp->v.TypeVar.name, DEF_TYPE_PARAM | DEF_LOCAL, LOCATION(tp)))
             VISIT_QUIT(st, 0);
-        if (tp->v.TypeVar.bound) {
-            int is_in_class = st->st_cur->ste_can_see_class_scope;
-            if (!symtable_enter_block(st, tp->v.TypeVar.name,
-                                      TypeVarBoundBlock, (void *)tp,
-                                      LOCATION(tp)))
-                VISIT_QUIT(st, 0);
-            st->st_cur->ste_can_see_class_scope = is_in_class;
-            if (is_in_class && !symtable_add_def(st, &_Py_ID(__classdict__), USE, LOCATION(tp->v.TypeVar.bound))) {
-                VISIT_QUIT(st, 0);
-            }
-            VISIT(st, expr, tp->v.TypeVar.bound);
-            if (!symtable_exit_block(st))
-                VISIT_QUIT(st, 0);
+
+        // We must use a different key for the bound and default. The obvious choice would be to
+        // use the .bound and .default_value pointers, but that fails when the expression immediately
+        // inside the bound or default is a comprehension: we would reuse the same key for
+        // the comprehension scope. Therefore, use the address + 1 as the second key.
+        // The only requirement for the key is that it is unique and it matches the logic in
+        // compile.c where the scope is retrieved.
+        if (!symtable_visit_type_param_bound_or_default(st, tp->v.TypeVar.bound, tp->v.TypeVar.name,
+                                                        (void *)tp)) {
+            VISIT_QUIT(st, 0);
+        }
+        if (!symtable_visit_type_param_bound_or_default(st, tp->v.TypeVar.default_value, tp->v.TypeVar.name,
+                                                        (void *)((uintptr_t)tp + 1))) {
+            VISIT_QUIT(st, 0);
         }
         break;
     case TypeVarTuple_kind:
-        if (!symtable_add_def(st, tp->v.TypeVarTuple.name, DEF_TYPE_PARAM | DEF_LOCAL, LOCATION(tp)))
+        if (!symtable_add_def(st, tp->v.TypeVarTuple.name, DEF_TYPE_PARAM | DEF_LOCAL, LOCATION(tp))) {
             VISIT_QUIT(st, 0);
+        }
+        if (!symtable_visit_type_param_bound_or_default(st, tp->v.TypeVarTuple.default_value, tp->v.TypeVarTuple.name,
+                                                        (void *)tp)) {
+            VISIT_QUIT(st, 0);
+        }
         break;
     case ParamSpec_kind:
-        if (!symtable_add_def(st, tp->v.ParamSpec.name, DEF_TYPE_PARAM | DEF_LOCAL, LOCATION(tp)))
+        if (!symtable_add_def(st, tp->v.ParamSpec.name, DEF_TYPE_PARAM | DEF_LOCAL, LOCATION(tp))) {
             VISIT_QUIT(st, 0);
+        }
+        if (!symtable_visit_type_param_bound_or_default(st, tp->v.ParamSpec.default_value, tp->v.ParamSpec.name,
+                                                        (void *)tp)) {
+            VISIT_QUIT(st, 0);
+        }
         break;
     }
     VISIT_QUIT(st, 1);