Add double_parens regression test for tracked function without arguments

Author: MichaReiser

tests/warnings/double_parens.rs

@@ -0,0 +1,39 @@
+//! Regression test for clippy::double_parens warnings in cycle macros.
+//!
+//! This test ensures that tracked functions with no additional inputs (beyond `db`)
+//! don't trigger clippy::double_parens warnings when using cycle_initial or cycle_fn.
+//!
+//! Before the fix in components/salsa-macro-rules/src/unexpected_cycle_recovery.rs,
+//! these macros would generate `std::mem::drop(())` which triggered the warning.
+//!
+//! See: https://github.com/salsa-rs/salsa/issues/1004
+
+// This tracked function has no additional inputs beyond `db`.
+// With the old code, this would trigger clippy::double_parens warnings in the
+// generated `unexpected_cycle_initial` and `unexpected_cycle_recovery` macros.
+#[salsa::tracked]
+fn simple_tracked_query(_db: &dyn salsa::Database) -> u32 {
+    100
+}
+
+// Tracked function with cycle recovery and no additional inputs.
+// The cycle_initial and cycle_fn functions also have no additional inputs beyond `db`,
+// which would trigger the clippy warning with the old code.
+#[salsa::tracked(cycle_fn=cycle_recover, cycle_initial=initial)]
+#[allow(dead_code)]
+fn query_with_cycle_support(_db: &dyn salsa::Database) -> u32 {
+    200
+}
+
+fn initial(_db: &dyn salsa::Database) -> u32 {
+    0
+}
+
+fn cycle_recover(
+    _db: &dyn salsa::Database,
+    value: &u32,
+    _count: u32,
+) -> salsa::CycleRecoveryAction<u32> {
+    // Just return the value to avoid actual cycling in this test
+    salsa::CycleRecoveryAction::Fallback(*value)
+}

tests/warnings/main.rs

@@ -2,6 +2,7 @@
 
 #![deny(warnings)]
 
+mod double_parens;
 mod needless_borrow;
 mod needless_lifetimes;
 mod unused_variable_db;