Add -release:8 to scalacOptions (#4649)

This ensures published Chisel artifacts work with Java 8--both in
generated bytecode (which was previously true because default setting is
-target:8), but also in disallowing APIs added in newer JDKs.

Also unify most handling of scalacOptions into new HasCommonOptions
trait.

Author: jackkoenig

build.mill

@@ -99,6 +99,7 @@ object v extends Module {
     "-unchecked",
     "-Werror",
     "-Ymacro-annotations",
+    "-release:8",
     "-explaintypes",
     "-Xcheckinit",
     "-Xlint:infer-any",
@@ -137,6 +138,15 @@ trait HasScala2Plugin extends CrossModuleBase {
   }
 }
 
+trait HasCommonOptions extends CrossModuleBase {
+  def xsource3: Boolean = true
+  override def scalacOptions = Task {
+    if (!v.isScala3(crossScalaVersion)) {
+      super.scalacOptions() ++ v.scala2CommonOptions ++ Option.when(xsource3)("-Xsource:3")
+    } else super.scalacOptions()
+  }
+}
+
 trait HasJextractGeneratedSources extends JavaModule {
 
   def jextractBinary: T[os.Path]

core/package.mill

@@ -13,21 +13,11 @@ object `package` extends RootModule {
   object cross extends Cross[Core](v.scalaCrossVersions)
 }
 
-trait Core extends CrossSbtModule with HasScala2MacroAnno with ScalafmtModule {
+trait Core extends CrossSbtModule with HasScala2MacroAnno with HasCommonOptions with ScalafmtModule {
   def scalaVersion = crossScalaVersion
 
   def millSourcePath = super.millSourcePath / os.up
 
-  override def scalacOptions = Task {
-    if (v.isScala3(crossScalaVersion)) {
-      Seq.empty[String]
-    } else {
-      v.scala2CommonOptions ++ Seq(
-        "-Xsource:3"
-      )
-    }
-  }
-
   val crossModuleDeps = Seq(firrtl.cross(crossScalaVersion)) ++ {
     if (v.isScala3(crossScalaVersion)) Seq.empty
     else Seq(macros.cross(crossScalaVersion))

firrtl/package.mill

@@ -12,23 +12,27 @@ object `package` extends RootModule {
   object cross extends Cross[Firrtl](v.scalaCrossVersions)
 }
 
-trait Firrtl extends CrossSbtModule with Cross.Module[String] with HasScala2MacroAnno with ScalafmtModule {
+trait Firrtl
+    extends CrossSbtModule
+    with Cross.Module[String]
+    with HasScala2MacroAnno
+    with HasCommonOptions
+    with ScalafmtModule {
   def scalaVersion = crossScalaVersion
 
   def millSourcePath = super.millSourcePath / os.up
 
   override def scalacOptions = Task {
-    if (v.isScala3(crossScalaVersion)) {
-      Seq.empty[String]
-    } else {
-      v.scala2CommonOptions ++ Seq(
-        "-language:reflectiveCalls",
-        "-language:existentials",
-        "-language:implicitConversions",
-        "-Yrangepos", // required by SemanticDB compiler plugin
-        "-Xsource:3",
-        "-Xsource-features:infer-override"
-      )
+    super.scalacOptions() ++ {
+      if (v.isScala3(crossScalaVersion)) Seq.empty[String]
+      else
+        Seq(
+          "-language:reflectiveCalls",
+          "-language:existentials",
+          "-language:implicitConversions",
+          "-Yrangepos", // required by SemanticDB compiler plugin
+          "-Xsource-features:infer-override"
+        )
     }
   }
 

integration-tests/package.mill

@@ -12,10 +12,13 @@ object `package` extends RootModule {
   object cross extends Cross[IntegrationTests](v.scalaCrossVersions)
 }
 
-trait IntegrationTests extends CrossSbtModule with HasScala2Plugin with ScalafmtModule {
+trait IntegrationTests extends CrossSbtModule with HasScala2Plugin with HasCommonOptions with ScalafmtModule {
   def pluginModule = plugin.cross()
   def millSourcePath = super.millSourcePath / os.up
 
+  // TODO enable
+  override def xsource3 = false
+
   object test extends SbtTests with TestModule.ScalaTest with ScalafmtModule {
     override def moduleDeps = super.moduleDeps :+ chisel().test
     def ivyDeps = Agg(v.scalatest, v.scalacheck)

macros/package.mill

@@ -12,19 +12,9 @@ object `package` extends RootModule {
   object cross extends Cross[Macros](v.scalaCrossVersions)
 }
 
-trait Macros extends CrossSbtModule with HasScala2MacroAnno with ScalafmtModule {
+trait Macros extends CrossSbtModule with HasScala2MacroAnno with HasCommonOptions with ScalafmtModule {
   def millSourcePath = super.millSourcePath / os.up
 
-  override def scalacOptions = Task {
-    if (v.isScala3(crossScalaVersion)) {
-      Seq.empty[String]
-    } else {
-      v.scala2CommonOptions ++ Seq(
-        "-Xsource:3"
-      )
-    }
-  }
-
   override def ivyDeps =
     if (!v.isScala3(crossScalaVersion)) {
       super.ivyDeps() ++ Seq(v.scalaReflect(crossScalaVersion))

plugin/package.mill

@@ -13,14 +13,17 @@ object `package` extends RootModule {
   object cross extends Cross[Plugin](v.pluginScalaCrossVersions)
 }
 
-trait Plugin extends CrossSbtModule with ScalafmtModule with release.ChiselPublishModule {
+trait Plugin extends CrossSbtModule with ScalafmtModule with HasCommonOptions with release.ChiselPublishModule {
   override def artifactName = "chisel-plugin"
 
   def millSourcePath = super.millSourcePath / os.up
 
   // The plugin is compiled for every minor Scala version
   override def crossFullScalaVersion = true
 
+  // There is no code sharing in the plugin so no point in -Xsource:3
+  override def xsource3 = false
+
   def scalaLibraryIvy = v.scalaLibrary(crossScalaVersion)
   def scalaReflectIvy = v.scalaReflect(crossScalaVersion)
   def scalaCompilerIvy: Dep = v.scalaCompiler(crossScalaVersion)

stdlib/package.mill

@@ -12,7 +12,7 @@ object `package` extends RootModule {
   object cross extends Cross[Stdlib](v.scalaCrossVersions)
 }
 
-trait Stdlib extends CrossSbtModule with HasScala2Plugin with ScalafmtModule {
+trait Stdlib extends CrossSbtModule with HasScala2Plugin with HasCommonOptions with ScalafmtModule {
   def millSourcePath = super.millSourcePath / os.up
   def chiselModule = chisel(crossScalaVersion)
   def pluginModule = plugin.cross(crossScalaVersion)

svsim/package.mill

@@ -12,18 +12,14 @@ object `package` extends RootModule {
   object cross extends Cross[Svsim](v.scalaCrossVersions)
 }
 
-trait Svsim extends CrossSbtModule with ScalafmtModule {
+trait Svsim extends CrossSbtModule with HasCommonOptions with ScalafmtModule {
   def millSourcePath = super.millSourcePath / os.up
 
   override def scalacOptions = Task {
-    if (v.isScala3(crossScalaVersion)) {
-      Seq.empty[String]
-    } else {
-      v.scala2CommonOptions ++ Seq(
-        "-Xsource:3",
+    super.scalacOptions() ++
+      Option.when(!v.isScala3(crossScalaVersion))(
         "-Xsource-features:case-apply-copy-access"
       )
-    }
   }
 
   object test extends SbtTests with TestModule.ScalaTest with ScalafmtModule {