Add checks for misuse or omission of Module()

Implemented by adding a Boolean to check for alternating invocations of object
Module.apply and the constructor of abstract class Module.
Fixes #192

2 files changed, 24 insertions, 1 deletions

diff --git a/chiselFrontend/src/main/scala/chisel3/core/Module.scala b/chiselFrontend/src/main/scala/chisel3/core/Module.scala
index c3353d85..ca391091 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Module.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Module.scala
@@ -25,9 +25,21 @@ object Module {
     // module de-duplication in FIRRTL emission.
     val childSourceInfo = UnlocatableSourceInfo
 
+    if (Builder.readyForModuleConstr) {
+      throwException("Error: Called Module() twice without instantiating a Module." +
+                     sourceInfo.makeMessage(" See " + _))
+    }
+    Builder.readyForModuleConstr = true
     val parent: Option[Module] = Builder.currentModule
-    val m = bc.setRefs() // This will set currentModule!
+
+    val m = bc.setRefs() // This will set currentModule and unset readyForModuleConstr!!!
     m._commands.prepend(DefInvalid(childSourceInfo, m.io.ref)) // init module outputs
+
+    if (Builder.readyForModuleConstr) {
+      throwException("Error: attempted to instantiate a Module, but nothing happened. " +
+                     "This is probably due to rewrapping a Module instance with Module()." +
+                     sourceInfo.makeMessage(" See " + _))
+    }
     Builder.currentModule = parent // Back to parent!
     val ports = m.computePorts
     val component = Component(m, m.name, ports, m._commands)
@@ -93,6 +105,10 @@ extends HasId {
   private[chisel3] val _commands = ArrayBuffer[Command]()
   private[core] val _ids = ArrayBuffer[HasId]()
   Builder.currentModule = Some(this)
+  if (!Builder.readyForModuleConstr) {
+    throwException("Error: attempted to instantiate a Module without wrapping it in Module().")
+  }
+  readyForModuleConstr = false
 
   /** Desired name of this module. */
   def desiredName = this.getClass.getName.split('.').last
diff --git a/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala b/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
index b4b0e028..028ce628 100644
--- a/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
+++ b/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
@@ -146,6 +146,9 @@ private[chisel3] class DynamicContext() {
   val globalNamespace = new Namespace(None, Set())
   val components = ArrayBuffer[Component]()
   var currentModule: Option[Module] = None
+  // Set by object Module.apply before calling class Module constructor
+  // Used to distinguish between no Module() wrapping, multiple wrappings, and rewrapping
+  var readyForModuleConstr: Boolean = false
   val errors = new ErrorLog
 }
 
@@ -170,6 +173,10 @@ private[chisel3] object Builder {
       // A bare api call is, e.g. calling Wire() from the scala console).
     )
   }
+  def readyForModuleConstr: Boolean = dynamicContext.readyForModuleConstr
+  def readyForModuleConstr_=(target: Boolean): Unit = {
+    dynamicContext.readyForModuleConstr = target
+  }
 
   // TODO(twigg): Ideally, binding checks and new bindings would all occur here
   // However, rest of frontend can't support this yet.