error: trailing semicolon in macro used in expression position
  --> $DIR/issue-84195-lint-anon-const.rs:8:14
   |
LL |     () => { 0; };
   |              ^
...
LL |     let val: [u8; len!()] = [];
   |                   ------ in this macro invocation
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
note: the lint level is defined here
  --> $DIR/issue-84195-lint-anon-const.rs:5:9
   |
LL | #![deny(semicolon_in_expressions_from_macros)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the macro `len` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error

Future incompatibility report: Future breakage diagnostic:
error: trailing semicolon in macro used in expression position
  --> $DIR/issue-84195-lint-anon-const.rs:8:14
   |
LL |     () => { 0; };
   |              ^
...
LL |     let val: [u8; len!()] = [];
   |                   ------ in this macro invocation
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
note: the lint level is defined here
  --> $DIR/issue-84195-lint-anon-const.rs:5:9
   |
LL | #![deny(semicolon_in_expressions_from_macros)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the macro `len` (in Nightly builds, run with -Z macro-backtrace for more info)