provide API to use absolute path for SourceInfo

- bug fix that chisel.project.root doesn't take effect
- if CHISEL_PROJECT_ROOT_ABSOLUTE is defined, use absolute path in
  chisel SourceInfo
- if CHISEL_PROJECT_ROOT_REPLACE is defined, replace CHISEL_PROJECT_ROOT
  or user.dir with it in chisel chisel SourceInfo

Author: sequencer

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

@@ -14,12 +14,28 @@ import scala.reflect.macros.blackbox.Context
 /** Scala compile-time function for determine the String used to represent a source file path in SourceInfos */
 private[internal] object SourceInfoFileResolver {
   def resolve(source: scala.reflect.internal.util.SourceFile): String = {
-    val userDir = sys.props.get("user.dir") // Figure out what to do if not provided
-    val projectRoot = sys.props.get("chisel.project.root")
+    val userDir = sys.props.get("user.dir")
+    val projectRoot = sys.env.get("CHISEL_PROJECT_ROOT")
+    val isAbs = sys.env.contains("CHISEL_PROJECT_ROOT_ABSOLUTE")
+    val projectRootReplace = sys.env.get("CHISEL_PROJECT_ROOT_REPLACE")
     val root = projectRoot.orElse(userDir)
 
     val path = root.map(r => source.file.canonicalPath.stripPrefix(r)).getOrElse(source.file.name)
     val pathNoStartingSlash = if (path(0) == '/') path.tail else path
-    pathNoStartingSlash
+
+    (root, isAbs, projectRootReplace) match {
+      case (None, _, _) =>
+        throw new Exception(s"Neither user.dir nor chisel.project.root is not defined.")
+      case (Some(_), true, None) =>
+        source.file.canonicalPath
+      case (Some(_), true, Some(projectRootReplace)) =>
+        s"$projectRootReplace/${pathNoStartingSlash}"
+      case (Some(_), false, Some(projectRootReplace)) =>
+        throw new Exception(
+          s"chisel.project.root.replace defined ${projectRootReplace}, but chisel.project.root.absolute is not defined"
+        )
+      case (Some(_), false, None) =>
+        pathNoStartingSlash
+    }
   }
 }