fix: evaluate target lazily in Path (#4543)

At the moment `toTarget` does not work properly with the D/I system,
seeing that we cannot get the instanceName of a module when evaluating
it, and even if we call `toTarget` in `atModuleBodyEnd` we will get the
wrong circuit name since the definition of the module's parent is still
in construction.

In order to construct `Path` properly, we need to defer the evaluation
of `target` to the IR generation time in the `isMember` constructor,
just as the other constructors already do.

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

Author: unlsycn

core/src/main/scala/chisel3/properties/Path.scala

@@ -106,8 +106,8 @@ object Path {
 
   /** Construct a Path from a target
     */
-  def apply(target: IsMember): Path = apply(target, false)
-  def apply(target: IsMember, isMemberPath: Boolean): Path = {
+  def apply(target: => IsMember): Path = apply(target, false)
+  def apply(target: => IsMember, isMemberPath: Boolean): Path = {
     val _isMemberPath = isMemberPath // avoid name shadowing below
     new TargetPath {
       def toTarget():   IsMember = target

src/test/scala/chiselTests/ToTargetSpec.scala

@@ -5,7 +5,7 @@ package chiselTests
 import chisel3._
 import chisel3.properties.{Path, Property}
 import circt.stage.ChiselStage
-import chisel3.experimental.hierarchy.{instantiable, public, Definition, Instance}
+import chisel3.experimental.hierarchy.{instantiable, public, Definition, Instance, Instantiate}
 
 @instantiable
 class RelativeInnerModule extends RawModule {
@@ -144,6 +144,20 @@ class RelativeSiblingsInstancesParent extends RawModule {
   }
 }
 
+class PathFromInstanceToTarget extends RawModule {
+  @instantiable
+  class Hierarchy1 extends RawModule {
+    @instantiable
+    class Hierarchy2 extends RawModule {
+      val target = Instantiate(new RelativeInnerModule)
+      @public val path = IO(Output(Property[Path]()))
+      path := Property(Path(target.toTarget))
+    }
+    val instance2 = Instantiate(new Hierarchy2)
+  }
+  val instance1 = Instantiate(new Hierarchy1)
+}
+
 class ToTargetSpec extends ChiselFlatSpec with Utils {
 
   var m: InstanceNameModule = _
@@ -290,4 +304,9 @@ class ToTargetSpec extends ChiselFlatSpec with Utils {
     e.getMessage should include("No common ancestor between")
   }
 
+  it should ("get correct Path from an Instance") in {
+    val chirrtl = ChiselStage.emitCHIRRTL(new PathFromInstanceToTarget)
+    chirrtl should include("OMInstanceTarget:~PathFromInstanceToTarget|Hierarchy2/target:RelativeInnerModule")
+  }
+
 }