In Nightly builds both cycle_initial and recover_from_cycle generate unnecessary parentheses warnings when using #[salsa::tracked] macro and the tracked function doesn't use any additional inputs:

= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#double_parens
= note: this error originates in the macro salsa::plumbing::unexpected_cycle_recovery which comes from the expansion of the attribute macro salsa::tracked (in Nightly builds, run with -Z macro-backtrace for more info)
= note: this error originates in the macro salsa::plumbing::unexpected_cycle_initial which comes from the expansion of the attribute macro salsa::tracked (in Nightly builds, run with -Z macro-backtrace for more info)

The Problem:

In components/salsa-macro-rules/src/unexpected_cycle_recovery.rs, both macros use this pattern: std::mem::drop(($($other_inputs,)*)); that creates a tuple containing all $other_inputs and drops them.

These macros are invoked from components/salsa-macro-rules/src/setup_tracked_fn.rs:305-316:

• cycle_initial is called with: (db, $($input_id),*)
• recover_from_cycle is called with: (db, value, count, $($input_id),*)

When $other_inputs is empty (function has no additional inputs beyond db), the expression ($($other_inputs,)*) expands to () (an empty tuple), resulting in: std::mem::drop(()) and it triggers clippy warnings.

The Fix:

Instead of creating a tuple and dropping it, we should repeat dropping each input individually:

• instead of std::mem::drop(($($other_inputs,)*));
• use $(std::mem::drop($other_inputs);)*