pub const MAX_INTERPOLATION_NESTING: usize = 32;Expand description
How deeply "…" literals may nest inside each other’s interpolation holes
(§8.1, ADR-147).
A hole holds a full expression, so "{f("{y}")}" is one literal containing
another and interp::text_end is recursive with the file’s own text. The
bound is what keeps adversarial input off the stack.
Unlike MAX_TEMPLATE_NESTING, reaching this bound does not change what a
delimiter means — it refuses to enter, and the literal is reported as
unterminated. That difference is deliberate: the lexer’s resume path only
ever runs for a literal the pre-scan proved closes, so a bound that answered
“closed, measured differently” would put the two on different rules at
exactly the depth nobody writes.