py/obj.h: Fix mp_seq_replace_slice_no_grow to use memmove not memcpy.

Because the argument arrays may overlap, as show by the new tests in this
commit.

Also remove the debugging comments for these macros, add a new comment
about overlapping regions, and separate the macros by blank lines to make
them easier to read.

Fixes issue #6244.

Signed-off-by: Damien George <damien@micropython.org>

py/obj.h

@@ -992,17 +992,17 @@ bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, size_t len1, const mp
 mp_obj_t mp_seq_index_obj(const mp_obj_t *items, size_t len, size_t n_args, const mp_obj_t *args);
 mp_obj_t mp_seq_count_obj(const mp_obj_t *items, size_t len, mp_obj_t value);
 mp_obj_t mp_seq_extract_slice(size_t len, const mp_obj_t *seq, mp_bound_slice_t *indexes);
+
 // Helper to clear stale pointers from allocated, but unused memory, to preclude GC problems
 #define mp_seq_clear(start, len, alloc_len, item_sz) memset((byte *)(start) + (len) * (item_sz), 0, ((alloc_len) - (len)) * (item_sz))
+
+// Note: dest and slice regions may overlap
 #define mp_seq_replace_slice_no_grow(dest, dest_len, beg, end, slice, slice_len, item_sz) \
-    /*printf("memcpy(%p, %p, %d)\n", dest + beg, slice, slice_len * (item_sz));*/ \
-    memcpy(((char *)dest) + (beg) * (item_sz), slice, slice_len * (item_sz)); \
-    /*printf("memmove(%p, %p, %d)\n", dest + (beg + slice_len), dest + end, (dest_len - end) * (item_sz));*/ \
+    memmove(((char *)dest) + (beg) * (item_sz), slice, slice_len * (item_sz)); \
     memmove(((char *)dest) + (beg + slice_len) * (item_sz), ((char *)dest) + (end) * (item_sz), (dest_len - end) * (item_sz));
 
 // Note: dest and slice regions may overlap
 #define mp_seq_replace_slice_grow_inplace(dest, dest_len, beg, end, slice, slice_len, len_adj, item_sz) \
-    /*printf("memmove(%p, %p, %d)\n", dest + beg + len_adj, dest + beg, (dest_len - beg) * (item_sz));*/ \
     memmove(((char *)dest) + (beg + slice_len) * (item_sz), ((char *)dest) + (end) * (item_sz), ((dest_len) + (len_adj) - ((beg) + (slice_len))) * (item_sz)); \
     memmove(((char *)dest) + (beg) * (item_sz), slice, slice_len * (item_sz));
 

tests/basics/memoryview_slice_assign.py

@@ -61,3 +61,27 @@ try:
     memoryview(array.array('i'))[0:2] = b'1234'
 except ValueError:
     print('ValueError')
+
+# test shift left of bytearray
+b = bytearray(range(10))
+mv = memoryview(b)
+mv[1:] = mv[:-1]
+print(b)
+
+# test shift right of bytearray
+b = bytearray(range(10))
+mv = memoryview(b)
+mv[:-1] = mv[1:]
+print(b)
+
+# test shift left of array
+a = array.array('I', range(10))
+mv = memoryview(a)
+mv[1:] = mv[:-1]
+print(a)
+
+# test shift right of array
+a = array.array('I', range(10))
+mv = memoryview(a)
+mv[:-1] = mv[1:]
+print(a)