Remove deprecated @usecase

This removes uses of @usecase. This is deprecated in Scala 2.13.x.
Additionally, scala generious spurious warnings if you use @usecase in
a non-abstract class. (It thinks that this is an abstract member of
something concrete.)

The guidance from upstream Scala is to be explicit about how to use
your API via @example.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

2 files changed, 19 insertions, 27 deletions

diff --git a/chiselFrontend/src/main/scala/chisel3/core/Data.scala b/chiselFrontend/src/main/scala/chisel3/core/Data.scala
index 7ff58b54..51ad154f 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Data.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Data.scala
@@ -567,9 +567,8 @@ abstract class Data extends HasId with NamedComponent with SourceInfoDoc { // sc
 }
 
 trait WireFactory {
-  /** @usecase def apply[T <: Data](t: T): T
-    *   Construct a [[Wire]] from a type template
-    *   @param t The template from which to construct this wire
+  /** Construct a [[Wire]] from a type template
+    * @param t The template from which to construct this wire
     */
   def apply[T <: Data](t: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     if (compileOptions.declaredTypeMustBeUnbound) {
@@ -681,29 +680,25 @@ object WireDefault {
     x
   }
 
-  /** @usecase def apply[T <: Data](t: T, init: DontCare.type): T
-    *   Construct a [[Wire]] with a type template and a [[DontCare]] default
-    *   @param t The type template used to construct this [[Wire]]
-    *   @param init The default connection to this [[Wire]], can only be [[DontCare]]
-    *   @note This is really just a specialized form of `apply[T <: Data](t: T, init: T): T` with [[DontCare]]
-    *   as `init`
+  /** Construct a [[Wire]] with a type template and a [[DontCare]] default
+    * @param t The type template used to construct this [[Wire]]
+    * @param init The default connection to this [[Wire]], can only be [[DontCare]]
+    * @note This is really just a specialized form of `apply[T <: Data](t: T, init: T): T` with [[DontCare]] as `init`
     */
   def apply[T <: Data](t: T, init: DontCare.type)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = { // scalastyle:ignore line.size.limit
     applyImpl(t, init)
   }
 
-  /** @usecase def apply[T <: Data](t: T, init: T): T
-    *   Construct a [[Wire]] with a type template and a default connection
-    *   @param t The type template used to construct this [[Wire]]
-    *   @param init The hardware value that will serve as the default value
+  /** Construct a [[Wire]] with a type template and a default connection
+    * @param t The type template used to construct this [[Wire]]
+    * @param init The hardware value that will serve as the default value
     */
   def apply[T <: Data](t: T, init: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     applyImpl(t, init)
   }
 
-  /** @usecase def apply[T <: Data](init: T): T
-    *   Construct a [[Wire]] with a default connection
-    *   @param init The hardware value that will serve as a type template and default value
+  /** Construct a [[Wire]] with a default connection
+    * @param init The hardware value that will serve as a type template and default value
     */
   def apply[T <: Data](init: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     val model = (init match {
diff --git a/chiselFrontend/src/main/scala/chisel3/core/Reg.scala b/chiselFrontend/src/main/scala/chisel3/core/Reg.scala
index 27156f8b..747fad73 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Reg.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Reg.scala
@@ -30,10 +30,9 @@ import chisel3.internal.sourceinfo.{SourceInfo}
   *
   */
 object Reg {
-  /** @usecase def apply[T <: Data](t: T): T
-    *   Construct a [[Reg]] from a type template with no initialization value (reset is ignored).
-    *   Value will not change unless the [[Reg]] is given a connection.
-    *   @param t The template from which to construct this wire
+  /** Construct a [[Reg]] from a type template with no initialization value (reset is ignored).
+    * Value will not change unless the [[Reg]] is given a connection.
+    * @param t The template from which to construct this wire
     */
   def apply[T <: Data](t: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     if (compileOptions.declaredTypeMustBeUnbound) {
@@ -143,10 +142,9 @@ object RegNext {
   * }}}
   */
 object RegInit {
-  /** @usecase def apply[T <: Data](t: T, init: T): T
-    *   Construct a [[Reg]] from a type template initialized to the specified value on reset
-    *   @param t The type template used to construct this [[Reg]]
-    *   @param init The value the [[Reg]] is initialized to on reset
+  /** Construct a [[Reg]] from a type template initialized to the specified value on reset
+    * @param t The type template used to construct this [[Reg]]
+    * @param init The value the [[Reg]] is initialized to on reset
     */
   def apply[T <: Data](t: T, init: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     if (compileOptions.declaredTypeMustBeUnbound) {
@@ -162,9 +160,8 @@ object RegInit {
     reg
   }
 
-  /** @usecase def apply[T <: Data](init: T): T
-    *   Construct a [[Reg]] initialized on reset to the specified value.
-    *   @param init Initial value that serves as a type template and reset value
+  /** Construct a [[Reg]] initialized on reset to the specified value.
+    * @param init Initial value that serves as a type template and reset value
     */
   def apply[T <: Data](init: T)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): T = {
     val model = (init match {