document code modifications

Author: paleolimbot

data-raw/update-s2.R

@@ -81,8 +81,17 @@ print_next <- function() {
   )
   cli::cat_bullet(
     "Fix zero-length array warnings under -Wpedantic by inserting __extension__ at the beginning ",
-    "of expressions declaring them (s2region_coverer.h#251, util/gtl/compact_array.h#124)"
+    "of expressions declaring them (s2region_coverer.h#271)"
   )
+  cli::cat_bullet(
+    "Fix compact_array zero-length array warning by disabling inline elements on gcc ",
+    "(util/gtl/compact_array.h#89)"
+  )
+  cli::cat_bullet(
+    "Fix sanitizer error for compact_array when increasing the size of a zero-length array ",
+    "by wrapping util/gtl/compact_array.h#396-397 with if (old_capacity > 0) {...}"
+  )
+
   cli::cat_bullet("Remove extra semi-colon at s2boolean_operation.h#376")
   cli::cat_bullet("Remove extra semi-colons because of FROMHOST_TYPE_MAP macro (utils/endian/endian.h#565)")
   cli::cat_bullet(

inst/include/s2/util/gtl/compact_array.h

@@ -86,6 +86,9 @@ class compact_array_base {
 #endif
 
   // Opportunistically consider allowing inlined elements.
+  // dd: this has to be disabled to pass CRAN checks, since there is a
+  // (potentially) zero-length array that is not the last element of the class (so
+  // this can't be silenced using __extension__)
 #if defined(_LP64) && defined(__GNUC__) && false
   // With 64-bit pointers, our approach is to form a 16-byte struct:
   //   [5 bytes for size, capacity, is_exponent and is_inlined]
@@ -393,6 +396,9 @@ class compact_array_base {
     value_allocator_type allocator;
 
     T* new_ptr = allocator.allocate(capacity());
+    // dd: this modification fixes a ASAN/UBSAN error, because
+    // when old_capacity is 0, Array() is nullptr, which is UB
+    // for memcpy.
     if (old_capacity > 0) {
       memcpy(new_ptr, Array(), old_capacity * sizeof(T));
       allocator.deallocate(Array(), old_capacity);