Re: [PATCH] tools/libxl: Make gentypes.py compatible with older Python

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 21/10/2025 5:23 pm, Anthony PERARD wrote:
> On Thu, Oct 16, 2025 at 10:06:13PM -0400, Jason Andryuk wrote:
>> removeprefix is only added in Python 3.9.
>>
>> Instead of the prefix removal, switch to passing in a "depth" parameter,
>> and incrementing it for each level.
>>
>> There is a slight change in the generated _libxl_types.c.  instances of
>> KeyedUnion increment depth without outputing any code.  The net result
>> is some cases where jso_sub_1 is followed by jso_sub_3.  As an example:
>>
>> _libxl_types.c
>> _libxl_types.c
>> @@ -5535,12 +5535,12 @@
>>                  if (!jso_sub_1)
>>                      goto out;
>>                  if (!libxl__string_is_default(&p->u.pty.path)) {
>> -                    json_object *jso_sub_2 = NULL;
>> -                    rc = libxl__string_gen_jso(&jso_sub_2, p->u.pty.path);
>> +                    json_object *jso_sub_3 = NULL;
>> +                    rc = libxl__string_gen_jso(&jso_sub_3, p->u.pty.path);
>>                      if (rc)
>>                          goto out;
>> -                    if (json_object_object_add(jso_sub_1, "path", 
>> jso_sub_2)) {
>> -                        json_object_put(jso_sub_2);
>> +                    if (json_object_object_add(jso_sub_1, "path", 
>> jso_sub_3)) {
>> +                        json_object_put(jso_sub_3);
>>                          goto out;
>>                      }
>>                  }
>>
>> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
>> ---
>> Here's an alternative approach to workaround removeprefix.
> Yeah, this version is less obscure about what's going on. Let's go for
> it.
>
> Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Thanks.  I'll take this version, and take the liberty of assuming that
the Release Ack is transferable to whichever solution the maintainers
prefer in the end.

>
>>  tools/libs/light/gentypes.py | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/libs/light/gentypes.py b/tools/libs/light/gentypes.py
>> index 006bea170a..0e45c04f49 100644
>> --- a/tools/libs/light/gentypes.py
>> +++ b/tools/libs/light/gentypes.py
>> @@ -377,15 +377,16 @@ def get_default_expr(f, nparent, fexpr):
>>      return "%s" % fexpr
>>  
>>  # For json-c gen_json functions
>> -def libxl_C_type_gen_jso(ty, v, indent = "    ", parent = None, 
>> scope_object = "jso"):
>> +def libxl_C_type_gen_jso(ty, v, indent = "    ", parent = None, 
>> scope_object = "jso", depth = 0):
>>      s = ""
>>      if parent is None:
>>          s += "json_object *jso;\n"
>>          s += "int rc;\n"
>> -        sub_scope_object = "jso_sub_1"
>> +        depth = 1
>>      else:
>> -        sub_scope_object = "jso_sub_%d" % 
>> (1+int(scope_object.removeprefix("jso_sub_")))
>> +        depth += 1
> We could simply do `depth += 1` regardless of the value of parent, it
> would have the same effect, since depth start at 0.

That makes the code even more simple, because it takes out the else. 
The net hunk is:

@@ -377,15 +377,14 @@ def get_default_expr(f, nparent, fexpr):
     return "%s" % fexpr
 
 # For json-c gen_json functions
-def libxl_C_type_gen_jso(ty, v, indent = "    ", parent = None, scope_object = 
"jso"):
+def libxl_C_type_gen_jso(ty, v, indent = "    ", parent = None, scope_object = 
"jso", depth = 0):
     s = ""
     if parent is None:
         s += "json_object *jso;\n"
         s += "int rc;\n"
-        sub_scope_object = "jso_sub_1"
-    else:
-        sub_scope_object = "jso_sub_%d" % 
(1+int(scope_object.removeprefix("jso_sub_")))
 
+    depth += 1
+    sub_scope_object = "jso_sub_%d" % depth
     if isinstance(ty, idl.Array):
         if parent is None:
             raise Exception("Array type must have a parent")


~Andrew