Fix conversion of step range to slice with negative step size

Author: mrkn

ext/pycall/pycall.c

@@ -1777,16 +1777,36 @@ pycall_pyslice_from_ruby(VALUE obj)
     rb_raise(rb_eTypeError, "unexpected argument type %s (expected Range or Enumerator generated by Range#step)", rb_class2name(CLASS_OF(obj)));
   }
 
-  if (!exclude_end) {
-    ssize_t end_i = NUM2SSIZET(end);
-    switch (end_i) {
-      case -1:
-        end = Qnil;
-        break;
-
-      default:
-        end = SSIZET2NUM(end_i + 1); /* TODO: limit check */
-        break;
+  if (!NIL_P(step) && NUM2SSIZET(step) < 0) {
+    if (!NIL_P(end)) {
+      if (!exclude_end) {
+        ssize_t end_i = NUM2SSIZET(end);
+        switch (end_i) {
+          case 0:
+            end = Qnil;
+            break;
+
+          default:
+            end = SSIZET2NUM(end_i - 1); /* TODO: limit check */
+            break;
+        }
+      }
+    }
+  }
+  else {
+    if (!NIL_P(end)) {
+      if (!exclude_end) {
+        ssize_t end_i = NUM2SSIZET(end);
+        switch (end_i) {
+          case -1:
+            end = Qnil;
+            break;
+
+          default:
+            end = SSIZET2NUM(end_i + 1); /* TODO: limit check */
+            break;
+        }
+      }
     }
   }
 

spec/pycall/pyobject_wrapper_spec.rb

@@ -149,6 +149,7 @@ module PyCall
           expect(list[0..0]).to eq(PyCall::List.new([1]))
           expect(list[0...0]).to eq(PyCall::List.new([]))
           expect(list[0..-1]).to eq(PyCall::List.new([*1..10]))
+          expect(list[nil..nil]).to eq(PyCall::List.new([*1..10]))
           expect(list[0...-1]).to eq(PyCall::List.new([*1..9]))
           expect(list[1..-2]).to eq(PyCall::List.new([*2..9]))
           expect(list[1...-2]).to eq(PyCall::List.new([*2..8]))
@@ -160,6 +161,11 @@ module PyCall
           list = PyCall::List.new([*1..10])
           expect(list[(1..-1).step(2)]).to eq(PyCall::List.new([2, 4, 6, 8, 10]))
           expect(list[(1..-2).step(2)]).to eq(PyCall::List.new([2, 4, 6, 8]))
+          expect(list[(nil..nil).step(-1)]).to eq(PyCall::List.new([*1..10].reverse))
+          expect(list[(-1..0).step(-1)]).to eq(PyCall::List.new([*1..10].reverse))
+          expect(list[(-1...0).step(-1)]).to eq(PyCall::List.new([*2..10].reverse))
+          expect(list[(-2..2).step(-2)]).to eq(PyCall::List.new([9, 7, 5, 3]))
+          expect(list[(-2...2).step(-2)]).to eq(PyCall::List.new([9, 7, 5]))
         end
       end
     end