member functions and memory

[alexjbest]

Currently we see the following error in Sage

sage: R.<y> = QQ[]
sage: K = NumberField(y^2-y-1,'a')
sage: A = pari(K).alginit([2,[[],[]],[0,0]])
sage: K(A.algb())
1
sage: K(A.algb())
---------------------------------------------------------------------------
SystemError                               Traceback (most recent call last)
Input In [20], in <cell line: 5>()
      3 A = pari(K).alginit([Integer(2),[[],[]],[Integer(0),Integer(0)]])
      4 K(A.algb())
----> 5 K(A.algb())

File cypari2/auto_gen.pxi:718, in cypari2.gen.Gen_base.algb()

File cypari2/stack.pyx:182, in cypari2.stack.new_gen()

File cypari2/stack.pyx:212, in cypari2.stack.new_gen_noclear()

SystemError: new_gen() argument not on PARI stack, not on PARI heap and not a universal constant

We hypothesised that this is because the member functions are treated differently by pari and gp, in pari.desc the prototype is marked with m to tell gp to copy the return value to the stack. Aurel explained this to me a bit after talking with Bill and I wrote the following patch based on my understanding of the situation but running ./tests/rundoctest.py gives memory leaks, so I guess it's not quite correct, expert advice would be great!

diff --git a/autogen/ret.py b/autogen/ret.py
index 2186297..a004430 100644
--- a/autogen/ret.py
+++ b/autogen/ret.py
@@ -54,6 +54,13 @@ class PariReturnGEN(PariReturn):
         s = "        return new_gen({name})\n"
         return s.format(name=self.name)
 
+class PariReturnmGEN(PariReturn):
+    def ctype(self):
+        return "GEN"
+    def return_code(self):
+        s = "        return copy_gen({name})\n"
+        return s.format(name=self.name)
+
 class PariReturnInt(PariReturn):
     def ctype(self):
         return "int"
@@ -78,7 +85,7 @@ class PariReturnVoid(PariReturn):
 
 pari_ret_types = {
         '':  PariReturnGEN,
-        'm': PariReturnGEN,
+        'm': PariReturnmGEN,
         'i': PariReturnInt,
         'l': PariReturnLong,
         'u': PariReturnULong,
diff --git a/cypari2/gen.pyx b/cypari2/gen.pyx
index 247b1ad..d371931 100644
--- a/cypari2/gen.pyx
+++ b/cypari2/gen.pyx
@@ -72,7 +72,7 @@ from .convert cimport PyObject_AsGEN, gen_to_integer
 from .pari_instance cimport (prec_bits_to_words, prec_words_to_bits,
                              default_bitprec, get_var)
 from .stack cimport (new_gen, new_gens2, new_gen_noclear,
-                     clone_gen, clear_stack, reset_avma,
+                     clone_gen, copy_gen, clear_stack, reset_avma,
                      remove_from_pari_stack, move_gens_to_heap)
 from .closure cimport objtoclosure
 
diff --git a/cypari2/pari_instance.pyx b/cypari2/pari_instance.pyx
index 1366ab4..494bb11 100644
--- a/cypari2/pari_instance.pyx
+++ b/cypari2/pari_instance.pyx
@@ -287,7 +287,7 @@ from .string_utils cimport to_string, to_bytes
 from .paridecl cimport *
 from .paripriv cimport *
 from .gen cimport Gen, objtogen
-from .stack cimport (new_gen, new_gen_noclear, clear_stack,
+from .stack cimport (new_gen, new_gen_noclear, clear_stack, clone_gen, copy_gen,
                      set_pari_stack_size, before_resize, after_resize)
 from .handle_error cimport _pari_init_error_handling
 from .closure cimport _pari_init_closure
diff --git a/cypari2/stack.pxd b/cypari2/stack.pxd
index 00ef3a0..40388fb 100644
--- a/cypari2/stack.pxd
+++ b/cypari2/stack.pxd
@@ -5,6 +5,7 @@ from .gen cimport Gen_base, Gen
 cdef Gen new_gen(GEN x)
 cdef new_gens2(GEN x, GEN y)
 cdef Gen new_gen_noclear(GEN x)
+cdef Gen copy_gen(GEN x)
 cdef Gen clone_gen(GEN x)
 cdef Gen clone_gen_noclear(GEN x)
 
diff --git a/cypari2/stack.pyx b/cypari2/stack.pyx
index 95a7f1b..1370d95 100644
--- a/cypari2/stack.pyx
+++ b/cypari2/stack.pyx
@@ -224,6 +224,12 @@ cdef Gen new_gen_noclear(GEN x):
     return z
 
 
+cdef Gen copy_gen(GEN x):
+    t = Gen_stack_new(x)
+    #remove_from_pari_stack(y)
+    clear_stack()
+    return t
+
 cdef Gen clone_gen(GEN x):
     x = gclone(x)
     clear_stack()

Original issue from code Aurel Page and Eloi Torrents were writing at CIRM