-exec ... {} + matched too aggressively

[tavianator]

$ find -exec echo '{}' foo + \;
. foo +
...
$ ./target/debug/find -exec echo '{}' foo + \;
Error: -exec [args...] + isn't supported yet. Only -exec [args...] ;

In fact, POSIX says

The end of the primary expression shall be punctuated by a <semicolon> or by a <plus-sign>. Only a <plus-sign> that immediately follows an argument containing only the two characters "{}" shall punctuate the end of the primary expression. Other uses of the <plus-sign> shall not be treated as special.