bpo-36961: Handle positional-only arguments in uparse.c (GH-13412)

Lib/test/test_future.py

@@ -183,6 +183,18 @@ class AnnotationsFutureTestCase(unittest.TestCase):
         eq('lambda a, b, c=True: a')
         eq("lambda a, b, c=True, *, d=1 << v2, e='str': a")
         eq("lambda a, b, c=True, *vararg, d, e='str', **kwargs: a + b")
+        eq("lambda a, /, b, c=True, *vararg, d, e='str', **kwargs: a + b")
+        eq('lambda x, /: x')
+        eq('lambda x=1, /: x')
+        eq('lambda x, /, y: x + y')
+        eq('lambda x=1, /, y=2: x + y')
+        eq('lambda x, /, y=1: x + y')
+        eq('lambda x, /, y=1, *, z=3: x + y + z')
+        eq('lambda x=1, /, y=2, *, z=3: x + y + z')
+        eq('lambda x=1, /, y=2, *, z: x + y + z')
+        eq('lambda x=1, y=2, z=3, /, w=4, *, l, l2: x + y + z + w + l + l2')
+        eq('lambda x=1, y=2, z=3, /, w=4, *, l, l2, **kwargs: x + y + z + w + l + l2')
+        eq('lambda x, /, y=1, *, z: x + y + z')
         eq('lambda x: lambda y: x + y')
         eq('1 if True else 2')
         eq('str or None if int or True else str or bytes or None')

Python/ast_unparse.c

@@ -193,22 +193,30 @@ static int
 append_ast_args(_PyUnicodeWriter *writer, arguments_ty args)
 {
     bool first;
-    Py_ssize_t i, di, arg_count, default_count;
+    Py_ssize_t i, di, arg_count, posonlyarg_count, default_count;
 
     first = true;
 
-    /* positional arguments with defaults */
+    /* positional-only and positional arguments with defaults */
+    posonlyarg_count = asdl_seq_LEN(args->posonlyargs);
     arg_count = asdl_seq_LEN(args->args);
     default_count = asdl_seq_LEN(args->defaults);
-    for (i = 0; i < arg_count; i++) {
+    for (i = 0; i < posonlyarg_count + arg_count; i++) {
         APPEND_STR_IF_NOT_FIRST(", ");
-        APPEND(arg, (arg_ty)asdl_seq_GET(args->args, i));
+        if (i < posonlyarg_count){
+            APPEND(arg, (arg_ty)asdl_seq_GET(args->posonlyargs, i));
+        } else {
+            APPEND(arg, (arg_ty)asdl_seq_GET(args->args, i-posonlyarg_count));
+        }
 
-        di = i - arg_count + default_count;
+        di = i - posonlyarg_count - arg_count + default_count;
         if (di >= 0) {
             APPEND_STR("=");
             APPEND_EXPR((expr_ty)asdl_seq_GET(args->defaults, di), PR_TEST);
         }
+        if (posonlyarg_count && i + 1 == posonlyarg_count) {
+            APPEND_STR(", /");
+        }
     }
 
     /* vararg, or bare '*' if no varargs but keyword-only arguments present */
@@ -251,7 +259,9 @@ static int
 append_ast_lambda(_PyUnicodeWriter *writer, expr_ty e, int level)
 {
     APPEND_STR_IF(level > PR_TEST, "(");
-    APPEND_STR(asdl_seq_LEN(e->v.Lambda.args->args) ? "lambda " : "lambda");
+    Py_ssize_t n_positional = (asdl_seq_LEN(e->v.Lambda.args->args) +
+                               asdl_seq_LEN(e->v.Lambda.args->posonlyargs));
+    APPEND_STR(n_positional ? "lambda " : "lambda");
     APPEND(args, e->v.Lambda.args);
     APPEND_STR(": ");
     APPEND_EXPR(e->v.Lambda.body, PR_TEST);