Remove autoSeedVar, use Boolean to distinguish suggested or autoSeed (backport #4252)

build.sbt

@@ -390,6 +390,8 @@ lazy val unipublish =
         ProblemFilters.exclude[ReversedMissingMethodProblem]("chisel3.internal.firrtl.ir#LitArg.cloneWithValue"),
         // chisel3.Bits is sealed
         ProblemFilters.exclude[ReversedMissingMethodProblem]("chisel3.Bits._padLit"),
+        // hasAutoSeed was package private
+        ProblemFilters.exclude[DirectMissingMethodProblem]("chisel3.*.hasAutoSeed"),
         // _circuit was package private
         ProblemFilters.exclude[DirectMissingMethodProblem]("chisel3.*._circuit"),
         ProblemFilters.exclude[DirectMissingMethodProblem]("chisel3.*._circuit_=")

core/src/main/scala/chisel3/Data.scala

@@ -320,8 +320,8 @@ abstract class Data extends HasId with NamedComponent with SourceInfoDoc {
   override def autoSeed(name: String): this.type = {
     topBindingOpt match {
       // Ports are special in that the autoSeed will keep the first name, not the last name
-      case Some(PortBinding(m)) if hasAutoSeed && Builder.currentModule.contains(m) => this
-      case _                                                                        => super.autoSeed(name)
+      case Some(PortBinding(m)) if hasSeed && Builder.currentModule.contains(m) => this
+      case _                                                                    => super.autoSeed(name)
     }
   }
 

core/src/main/scala/chisel3/internal/Builder.scala

@@ -127,17 +127,16 @@ private[chisel3] trait HasId extends chisel3.InstanceId {
   override def hashCode: Int = super.hashCode()
   override def equals(that: Any): Boolean = super.equals(that)
 
-  // Contains suggested seed (user-decided seed)
+  // Did the user suggest a name? This overrides names suggested by the compiler plugin.
+  private var _nameIsSuggested: Boolean = false
+  // Contains name seed (either user suggested or generated by the plugin).
   private var suggested_seedVar: String = null // using nullable var for better memory usage
   private def suggested_seed:    Option[String] = Option(suggested_seedVar)
 
-  // Contains the seed computed automatically by the compiler plugin
-  private var auto_seedVar: String = null // using nullable var for better memory usage
-  private def auto_seed:    Option[String] = Option(auto_seedVar)
-
   // Prefix for use in naming
   // - Defaults to prefix at time when object is created
   // - Overridden when [[suggestSeed]] or [[autoSeed]] is called
+  // - Note that suggestSeed does *not* prevent autoSeed from changing this
   private var naming_prefix: Prefix = Builder.getPrefix
 
   /** Takes the last seed suggested. Multiple calls to this function will take the last given seed, unless
@@ -155,7 +154,9 @@ private[chisel3] trait HasId extends chisel3.InstanceId {
   private[chisel3] def autoSeed(seed: String): this.type = forceAutoSeed(seed)
   // Bypass the overridden behavior of autoSeed in [[Data]], apply autoSeed even to ports
   private[chisel3] def forceAutoSeed(seed: String): this.type = {
-    auto_seedVar = seed
+    if (!_nameIsSuggested) {
+      suggested_seedVar = seed
+    }
     naming_prefix = Builder.getPrefix
     this
   }
@@ -182,10 +183,11 @@ private[chisel3] trait HasId extends chisel3.InstanceId {
     * @return this object
     */
   def suggestName(seed: => String): this.type = {
-    if (suggested_seed.isEmpty) {
+    if (!_nameIsSuggested) {
       suggested_seedVar = seed
       // Only set the prefix if a seed hasn't been suggested
       naming_prefix = Builder.getPrefix
+      _nameIsSuggested = true
     }
     this
   }
@@ -204,13 +206,11 @@ private[chisel3] trait HasId extends chisel3.InstanceId {
     *
     * @return the current calculation of a name, if it exists
     */
-  private[chisel3] def seedOpt: Option[String] = suggested_seed.orElse(auto_seed)
+  private[chisel3] def seedOpt: Option[String] = suggested_seed
 
   /** @return Whether either autoName or suggestName has been called */
   def hasSeed: Boolean = seedOpt.isDefined
 
-  private[chisel3] def hasAutoSeed: Boolean = auto_seed.isDefined
-
   // Uses a namespace to convert suggestion into a true name
   // Will not do any naming if the reference already assigned.
   // (e.g. tried to suggest a name to part of a Record)