Bugfix: .toDefinition should update Builder.definitions (#5197)

* Calling .toDefinition should update Builder.definitions

* Ran formatter on tests

* Add test for two .toDefinition calls

Author: azidar

core/src/main/scala/chisel3/experimental/hierarchy/core/Instance.scala

@@ -67,8 +67,15 @@ final case class Instance[+A] private[chisel3] (private[chisel3] val underlying:
   }
 
   /** Returns the definition of this Instance */
-  override def toDefinition: Definition[A] = new Definition(Proto(proto))
-  override def toInstance:   Instance[A] = this
+  override def toDefinition: Definition[A] = {
+    val result = new Definition(Proto(proto))
+    // Because we are creating a new Definition, we should update our Builder.definitions
+    if (Builder.inContext && !Builder.definitions.view.map(_.proto).contains(result.proto)) {
+      Builder.definitions += result
+    }
+    result
+  }
+  override def toInstance: Instance[A] = this
   private[chisel3] def copy[T](underlying: Underlying[T]) = new Instance(underlying)
 
 }

src/test/scala-2/chiselTests/experimental/hierarchy/DefinitionSpec.scala

@@ -945,4 +945,59 @@ class DefinitionSpec extends AnyFunSpec with Matchers with FileCheck {
         )
     }
   }
+  describe("(9): Calling .toDefinition should update Builder.definitions") {
+    it("(9.a): calling .toDefinition from another definition's child Instance should work as expected") {
+      class Bar extends RawModule {
+        val a = WireInit(false.B)
+      }
+      @instantiable
+      class Foo extends RawModule {
+        @public val bar = Module(new Bar)
+      }
+      class Baz(d: Definition[Foo]) extends RawModule {
+        val bar = Instance(d.bar.toDefinition)
+      }
+      ChiselStage
+        .emitCHIRRTL(
+          {
+            val d = Definition(new Foo)
+            new Baz(d)
+          },
+          Array("--full-stacktrace")
+        )
+        .fileCheck()(
+          """|CHECK: module Bar :
+             |CHECK: module Baz :
+             |""".stripMargin
+        )
+    }
+    it("(9.b): calling .toDefinition twice from anther definition's child Instance should work as expected") {
+      class Bar extends RawModule {
+        val a = WireInit(false.B)
+      }
+      @instantiable
+      class Foo extends RawModule {
+        @public val bar = Module(new Bar)
+      }
+      class Baz(d: Definition[Foo]) extends RawModule {
+        val bar = Instance(d.bar.toDefinition)
+        val bar2 = Instance(d.bar.toDefinition)
+      }
+      val x = ChiselStage
+        .emitCHIRRTL(
+          {
+            val d = Definition(new Foo)
+            new Baz(d)
+          },
+          Array("--full-stacktrace")
+        )
+        .fileCheck()(
+          """|CHECK: module Bar :
+             |CHECK-NOT: module Bar_
+             |CHECK: module Baz :
+             |""".stripMargin
+        )
+    }
+  }
+
 }