printf: use non-zero indexes #7855
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#7837 added support for indexing in format strings, but allowed for an index of 0, treating it as equivalent to an index of 1. GNU rejects 0 indexes, which makes sense, as all the other indexes are 1-indexed, which means a user could encounter difficult to debug off-by-one errors if printf didn't return an error (e.g., if looping indexes from
0..$n).This commit forbids 0 indexes, expressed at the type level with
std::num::NonZero. Doing so also cuts the aligned size ofArgumentLocationin half, from two pointer widths to one, which is the sort of thing that could help some optimizations (I didn't run any benchmarks, the benefit is likely pretty tiny).