Deprecate auto-application of empty argument lists to parameterless functions (#2124)

* Migrate nullary funcs to parameterless versions
* Make deprecation message and dummy arguments clear and consistent

Co-authored-by: Megan Wachs <megan@sifive.com>

2 files changed, 10 insertions, 4 deletions

diff --git a/src/main/scala/chisel3/compatibility.scala b/src/main/scala/chisel3/compatibility.scala
index dde2321d..ffbb7e27 100644
--- a/src/main/scala/chisel3/compatibility.scala
+++ b/src/main/scala/chisel3/compatibility.scala
@@ -33,7 +33,10 @@ package object Chisel {
   implicit class AddDirectionToData[T<:Data](target: T) {
     def asInput: T = Input(target)
     def asOutput: T = Output(target)
-    def flip(): T = Flipped(target)
+    def flip: T = Flipped(target)
+
+    @deprecated("Calling this function with an empty argument list is invalid in Scala 3. Use the form without parentheses instead", "Chisel 3.5")
+    def flip(dummy: Int*): T = flip
   }
 
   implicit class AddDirMethodToData[T<:Data](target: T) {
diff --git a/src/main/scala/chisel3/util/Decoupled.scala b/src/main/scala/chisel3/util/Decoupled.scala
index 0e05d114..060a684c 100644
--- a/src/main/scala/chisel3/util/Decoupled.scala
+++ b/src/main/scala/chisel3/util/Decoupled.scala
@@ -37,7 +37,10 @@ object ReadyValidIO {
 
     /** Indicates if IO is both ready and valid
      */
-    def fire(): Bool = target.ready && target.valid
+    def fire: Bool = target.ready && target.valid
+
+    @deprecated("Calling this function with an empty argument list is invalid in Scala 3. Use the form without parentheses instead", "Chisel 3.5")
+    def fire(dummy: Int = 0): Bool = fire
 
     /** Push dat onto the output bits of this interface to let the consumer know it has happened.
       * @param dat the values to assign to bits.
@@ -222,8 +225,8 @@ class Queue[T <: Data](val gen: T,
   val ptr_match = enq_ptr.value === deq_ptr.value
   val empty = ptr_match && !maybe_full
   val full = ptr_match && maybe_full
-  val do_enq = WireDefault(io.enq.fire())
-  val do_deq = WireDefault(io.deq.fire())
+  val do_enq = WireDefault(io.enq.fire)
+  val do_deq = WireDefault(io.deq.fire)
   val flush = io.flush.getOrElse(false.B) 
 
   // when flush is high, empty the queue