[PATCH v2 0/2] rust: add unsafe precondition assertions to Vec length helpers

[JX <1239989762@qq.com>]

The safety requirements of `Vec::inc_len` and `Vec::dec_len` are
currently checked with `debug_assert!`. Convert them to
`unsafe_precondition_assert!` so violations are reported consistently
with other unsafe precondition failures.

The first patch makes the no-message form of
`unsafe_precondition_assert!` usable from const functions. This is
needed by `Vec::inc_len`, which is const, and avoids runtime formatting.

The second patch converts both Vec length helpers.

The series has been checked with:

  make rustfmtcheck
  make CLIPPY=1 rust/kernel.o
  make rusttest
  make rustdoc

Changes in v2:
- Use a fixed diagnostic literal instead of concatenating the stringified
  condition into a format string, since conditions may contain braces.
- Add a const-context documentation example with a block expression.

Link: https://lore.kernel.org/r/20260908080604.34070-1-1239989762@qq.com

JX (2):
  rust: make unsafe_precondition_assert! const compatible
  rust: alloc: use unsafe_precondition_assert! in Vec length helpers

 rust/kernel/alloc/kvec.rs |  7 ++++---
 rust/kernel/safety.rs     | 11 ++++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)


base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.54.0