Deprecate Chisel._ Compatibility Mode (#2668)

Author: mwachs5

docs/src/appendix/chisel3-vs-chisel2.md

@@ -9,6 +9,8 @@ section: "chisel3"
 import chisel3._
 ```
 
+**Note** Chisel2 Compatibility Mode is entirely deprecated in 3.6, so this entire page is relevant only for 3.6 and earlier.
+
 ## Chisel2 Migration
 For those moving from Chisel2, there were some backwards incompatible changes
 and your RTL needs to be modified to work with Chisel3. The required

src/main/scala/chisel3/compatibility.scala

@@ -27,7 +27,11 @@ object log2Up {
   // https://github.com/freechipsproject/chisel3/issues/847
   //@chiselRuntimeDeprecated
   //@deprecated("Use log2Ceil instead", "chisel3")
-  def apply(in: BigInt): Int = Chisel.log2Up(in)
+  def apply(in: BigInt): Int = {
+    require(in >= 0)
+    1.max((in - 1).bitLength)
+  }
+  def apply(in: Int): Int = apply(BigInt(in))
 }
 
 /** Compute the log2 of a Scala integer, rounded up.
@@ -66,7 +70,8 @@ object log2Down {
   // https://github.com/freechipsproject/chisel3/issues/847
   //@chiselRuntimeDeprecated
   //@deprecated("Use log2Floor instead", "chisel3")
-  def apply(in: BigInt): Int = Chisel.log2Down(in)
+  def apply(in: BigInt): Int = log2Up(in) - (if (isPow2(in)) 0 else 1)
+  def apply(in: Int):    Int = apply(BigInt(in))
 }
 
 /** Compute the log2 of a Scala integer, rounded down.

src/main/scala/chisel3/util/Math.scala

@@ -5,6 +5,8 @@ import chisel3.util.Decoupled
 import chisel3.stage.ChiselStage
 import chisel3.testers.BasicTester
 
+import scala.annotation.nowarn
+
 class BulkConnectSpec extends ChiselPropSpec {
   property("Chisel connects should emit FIRRTL bulk connects when possible") {
     val chirrtl = ChiselStage.emitChirrtl(new Module {
@@ -22,6 +24,7 @@ class BulkConnectSpec extends ChiselPropSpec {
   }
 
   property("Chisel connects should not emit FIRRTL bulk connects for Stringly-typed connections") {
+    @nowarn("msg=Chisel compatibility mode is deprecated")
     object Foo {
       import Chisel._
       // Chisel._ bundle

src/test/scala/chiselTests/BulkConnectSpec.scala

@@ -5,7 +5,10 @@ package chiselTests
 import scala.collection.immutable.ListMap
 import chisel3.stage.ChiselStage.emitChirrtl
 
+import scala.annotation.nowarn
+
 // Keep Chisel._ separate from chisel3._ below
+@nowarn("msg=Chisel compatibility mode is deprecated")
 object CompatibilityComponents {
   import Chisel._
   import Chisel3Components._
@@ -75,6 +78,7 @@ object Chisel3Components {
   class Chisel3ModuleChiselRecordB extends Chisel3PassthroughModule(Flipped(new ChiselRecord))
 }
 
+@nowarn("msg=Chisel compatibility mode is deprecated")
 class CompatibilityInteroperabilitySpec extends ChiselFlatSpec {
 
   "Modules defined in the Chisel._" should "successfully bulk connect in chisel3._" in {

src/test/scala/chiselTests/CompatibilityInteroperabilitySpec.scala

@@ -9,8 +9,10 @@ import org.scalacheck.Gen
 import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
 
 import scala.collection.immutable.ListMap
+import scala.annotation.nowarn
 
 // Need separate import to override compile options from Chisel._
+@nowarn("msg=Chisel compatibility mode is deprecated")
 object CompatibilityCustomCompileOptions {
   import Chisel.{defaultCompileOptions => _, _}
   implicit val customCompileOptions =
@@ -20,6 +22,7 @@ object CompatibilityCustomCompileOptions {
   }
 }
 
+@nowarn("msg=Chisel compatibility mode is deprecated")
 class CompatibilitySpec extends ChiselFlatSpec with ScalaCheckDrivenPropertyChecks with Utils {
   import Chisel._
 

src/test/scala/chiselTests/CompatibilitySpec.scala

@@ -6,6 +6,9 @@ import chisel3._
 import chisel3.CompileOptions._
 import chisel3.stage.ChiselStage
 
+import scala.annotation.nowarn
+
+@nowarn("msg=Chisel compatibility mode is deprecated")
 class CompileOptionsSpec extends ChiselFlatSpec with Utils {
 
   abstract class StrictModule extends Module()(chisel3.ExplicitCompileOptions.Strict)

src/test/scala/chiselTests/CompileOptionsTest.scala

@@ -8,6 +8,9 @@ import chisel3.ExplicitCompileOptions
 
 import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
 
+import scala.annotation.nowarn
+
+@nowarn("msg=Chisel compatibility mode is deprecated")
 object MigrationExamples {
   object InferResets {
     import Chisel.{defaultCompileOptions => _, _}
@@ -86,6 +89,7 @@ object MigrationExamples {
   }
 }
 
+@nowarn("msg=Chisel compatibility mode is deprecated")
 class MigrateCompileOptionsSpec extends ChiselFunSpec with Utils {
   import Chisel.{defaultCompileOptions => _, _}
   import chisel3.RequireSyncReset

src/test/scala/chiselTests/MigrateCompileOptionsSpec.scala

@@ -4,6 +4,9 @@ package chiselTests
 
 import chisel3.stage.ChiselStage
 
+import scala.annotation.nowarn
+
+@nowarn("msg=Chisel compatibility mode is deprecated")
 class ModuleExplicitResetSpec extends ChiselFlatSpec {
 
   "A Module with an explicit reset in compatibility mode" should "elaborate" in {