We pass the expression multi_category in to our verbose_multi macros, but because it's a macro we evaluate the expression 3 separate times. clang-analyzer reports a warning for this as the ternary passed in as multi_category could evaluate to a two-category struct the first evaluation, but a one-category struct in the second. In the following code
for (__v_idx = 0; __v_idx < multi_category.cnt; __v_idx++) { \ if (WT_VERBOSE_ISSET(session, multi_category.categories[__v_idx])) { \
 
The first multi_category could return an array with two verbose categories, so __v_idx iterates up to index 1, while the second multi_category evaluates to an array length 1 and we access past the end of the array.