diff --git a/Makefile b/Makefile
index 1911b29f700..4b54fcec247 100644
--- a/Makefile
+++ b/Makefile
@@ -53,7 +53,7 @@ pylint-hailtop:
 
 .PHONY: check-hail
 check-hail: check-hail-fast pylint-hailtop
-	cd hail && sh millw __.checkFormat + __.fix --check
+	cd hail && sh mill __.checkFormat + __.fix --check
 
 .PHONY: check-services
 check-services: $(CHECK_SERVICES_MODULES)
diff --git a/build.yaml b/build.yaml
index e2841fa1af2..cf1938b499d 100644
--- a/build.yaml
+++ b/build.yaml
@@ -724,7 +724,7 @@ steps:
       cd /io/repo/hail
 
       export MILLOPTS='--no-server' HAIL_RELEASE_MODE=1
-      time retry sh millw --no-server --version
+      time retry sh mill --no-server --version
 
       # We've encountered the following sporadic error in CI between `mill`
       # finishing assembling the jar and `Make` copying the jar:
@@ -770,7 +770,7 @@ steps:
       cd /io/repo/hail
 
       export MILLOPTS='--no-server'
-      time retry sh millw --no-server --version
+      time retry sh mill --no-server --version
 
       # See `build_hail_jar_and_wheel`
       time retry make shadowJar
@@ -803,7 +803,7 @@ steps:
       cd /io/repo/hail
 
       export MILLOPTS='--no-server'
-      time retry sh millw --no-server --version
+      time retry sh mill --no-server --version
 
       # See `build_hail_jar_and_wheel`
       time retry make shadowTestJar
@@ -863,7 +863,7 @@ steps:
       cd /io/repo/hail
 
       export SPARK_VERSION="3.0.2" SCALA_VERSION="2.12.13" HAIL_RELEASE_MODE=1 MILLOPTS='--no-server'
-      time retry sh millw --no-server --version
+      time retry sh mill --no-server --version
 
       # See `build_hail_jar_and_wheel`
       time retry make shadowJar
diff --git a/hail/.mill-version b/hail/.mill-version
index b80f98e66f1..e01e0ddd8e8 100644
--- a/hail/.mill-version
+++ b/hail/.mill-version
@@ -1 +1 @@
-0.11.7
+0.12.4
diff --git a/hail/Makefile b/hail/Makefile
index c4d4846efc8..fa06d1eec31 100644
--- a/hail/Makefile
+++ b/hail/Makefile
@@ -49,7 +49,7 @@ CLOUD_HAIL_DOCTEST_DATA_DIR = $(CLOUD_HAIL_TEST_RESOURCES_PREFIX)/doctest/data/
 
 # mill integration
 
-MILL := bash millw
+MILL := bash mill
 MILLOPTS ?=
 
 .PHONY: mill-clean
diff --git a/hail/build.sc b/hail/build.mill
similarity index 79%
rename from hail/build.sc
rename to hail/build.mill
index 96a3baf26c2..35f3e2be318 100644
--- a/hail/build.sc
+++ b/hail/build.mill
@@ -1,5 +1,7 @@
-import $ivy.`com.goyeau::mill-scalafix::0.3.2`
-import $ivy.`de.tototec::de.tobiasroeser.mill.vcs.version::0.4.0`
+package build
+
+import $ivy.`com.goyeau::mill-scalafix::0.4.2`
+import $ivy.`de.tototec::de.tobiasroeser.mill.vcs.version::0.4.1`
 import com.goyeau.mill.scalafix.ScalafixModule
 import de.tobiasroeser.mill.vcs.version.VcsVersion
 import mill._
@@ -15,56 +17,6 @@ object Settings {
   val hailPatchVersion = "133"
 }
 
-/** Update the millw script. */
-def millw(): Command[PathRef] = T.command {
-  val target =
-    mill.util.Util.download("https://raw.githubusercontent.com/lefou/millw/main/millw")
-  val millw = T.workspace / "millw"
-  os.copy.over(target.path, millw)
-  os.perms.set(millw, os.perms(millw) + java.nio.file.attribute.PosixFilePermission.OWNER_EXECUTE)
-  target
-}
-
-def scalaVersion: T[String] = T.input {
-  val v = T.ctx().env.getOrElse("SCALA_VERSION", "2.12.15")
-  if (!v.startsWith("2.12"))
-    Result.Failure("Hail currently supports only Scala 2.12")
-  else
-    v
-}
-
-def javaVersion: T[String] = T.input {
-  System.getProperty("java.version")
-}
-
-def sparkVersion: T[String] = T.input {
-  Result.Success(T.ctx().env.getOrElse("SPARK_VERSION", "3.5.0"))
-}
-
-def debugMode: T[Boolean] = T.input {
-  val isDebug = !T.ctx().env.contains("HAIL_RELEASE_MODE")
-  T.log.info(s"Building in ${if (isDebug) "debug" else "release"} mode")
-  isDebug
-}
-
-def debugOrRelease: Task[String] = T.task {
-  if (debugMode()) "debug" else "release"
-}
-
-def buildInfo: T[PathRef] = T {
-  val revision = VcsVersion.vcsState().currentRevision
-  os.write(
-    T.dest / "build-info.properties",
-    s"""[Build Metadata]
-       |revision=$revision
-       |sparkVersion=${sparkVersion()}
-       |hailPipVersion=${Settings.hailMajorMinorVersion}.${Settings.hailPatchVersion}
-       |hailBuildConfiguration=${debugOrRelease()}
-       |""".stripMargin,
-  )
-  PathRef(T.dest)
-}
-
 object Deps {
   object HTTPComponents {
     val core = ivy"org.apache.httpcomponents:httpcore:4.4.14"
@@ -94,8 +46,8 @@ object Deps {
   }
 
   object Spark {
-    def core: Task[Dep] = T.task(ivy"org.apache.spark::spark-core:${sparkVersion()}")
-    def mllib: Task[Dep] = T.task(ivy"org.apache.spark::spark-mllib:${sparkVersion()}")
+    def core: Task[Dep] = Task.Anon(ivy"org.apache.spark::spark-core:${build.env.sparkVersion()}")
+    def mllib: Task[Dep] = Task.Anon(ivy"org.apache.spark::spark-mllib:${build.env.sparkVersion()}")
   }
 
   val samtools = ivy"com.github.samtools:htsjdk:3.0.5"
@@ -121,13 +73,13 @@ object Deps {
 }
 
 trait HailScalaModule extends SbtModule with ScalafmtModule with ScalafixModule { outer =>
-  override def scalaVersion: T[String] = build.scalaVersion()
+  override def scalaVersion: T[String] = build.env.scalaVersion()
 
   override def javacOptions: T[Seq[String]] = Seq(
     "-Xlint:all",
     "-Werror",
-    if (debugMode()) "-g" else "-O",
-  ) ++ (if (!javaVersion().startsWith("1.8")) Seq("-Xlint:-processing") else Seq())
+    if (build.env.debugMode()) "-g" else "-O",
+  ) ++ (if (!build.env.javaVersion().startsWith("1.8")) Seq("-Xlint:-processing") else Seq())
 
   override def scalacOptions: T[Seq[String]] = T {
     Seq(
@@ -139,8 +91,9 @@ trait HailScalaModule extends SbtModule with ScalafmtModule with ScalafixModule
       "-Yno-adapted-args", // will be removed in 2.13
       "-Xlint",
       "-Ywarn-unused:_,-explicits,-implicits",
+      "-Wconf:msg=legacy-binding:s",
     ) ++ (
-      if (debugMode()) Seq()
+      if (build.env.debugMode()) Seq()
       else Seq(
         "-Xfatal-warnings",
         "-opt:l:method",
@@ -153,7 +106,7 @@ trait HailScalaModule extends SbtModule with ScalafmtModule with ScalafixModule
   override def bspCompileClasspath: T[Agg[UnresolvedPath]] =
     super.bspCompileClasspath() ++ resources().map(p => UnresolvedPath.ResolvedPath(p.path))
 
-  trait HailTests extends SbtModuleTests with TestNg with ScalafmtModule with ScalafixModule {
+  trait HailTests extends SbtTests with TestNg with ScalafmtModule with ScalafixModule {
     override def forkArgs: T[Seq[String]] = Seq("-Xss4m", "-Xmx4096M")
 
     override def ivyDeps: T[Agg[Dep]] =
@@ -171,7 +124,50 @@ trait HailScalaModule extends SbtModule with ScalafmtModule with ScalafixModule
   }
 }
 
-object main extends RootModule with HailScalaModule { outer =>
+object `package` extends RootModule with HailScalaModule { outer =>
+
+  object env extends Module {
+    def scalaVersion: T[String] = Task.Input {
+      val v = T.ctx().env.getOrElse("SCALA_VERSION", "2.12.20")
+      if (!v.startsWith("2.12"))
+        Result.Failure("Hail currently supports only Scala 2.12")
+      else
+        v
+    }
+
+    def javaVersion: T[String] = Task.Input {
+      System.getProperty("java.version")
+    }
+
+    def sparkVersion: T[String] = Task.Input {
+      Result.Success(T.ctx().env.getOrElse("SPARK_VERSION", "3.5.0"))
+    }
+
+    def debugMode: T[Boolean] = Task.Input {
+      val isDebug = !T.ctx().env.contains("HAIL_RELEASE_MODE")
+      T.log.info(s"Building in ${if (isDebug) "debug" else "release"} mode")
+      isDebug
+    }
+
+    def debugOrRelease: Task[String] = Task.Anon {
+      if (debugMode()) "debug" else "release"
+    }
+  }
+
+  def buildInfo: T[PathRef] = T {
+    val revision = VcsVersion.vcsState().currentRevision
+    os.write(
+      T.dest / "build-info.properties",
+      s"""[Build Metadata]
+         |revision=$revision
+         |sparkVersion=${env.sparkVersion()}
+         |hailPipVersion=${Settings.hailMajorMinorVersion}.${Settings.hailPatchVersion}
+         |hailBuildConfiguration=${env.debugOrRelease()}
+         |""".stripMargin,
+    )
+    PathRef(T.dest)
+  }
+
   override def moduleDeps: Seq[JavaModule] = Seq(memory)
 
   override def resources: T[Seq[PathRef]] = Seq(
@@ -256,15 +252,15 @@ object main extends RootModule with HailScalaModule { outer =>
 
     override def javacOptions: T[Seq[String]] =
       outer.javacOptions() ++ (
-        if (javaVersion().startsWith("1.8")) Seq(
+        if (env.javaVersion().startsWith("1.8")) Seq(
           "-XDenableSunApiLintControl",
           "-Xlint:-sunapi",
         )
         else Seq()
       )
 
-    override def sources: T[Seq[PathRef]] = T.sources {
-      Seq(PathRef(this.millSourcePath / os.up / "src" / debugOrRelease() / "java"))
+    override def sources: T[Seq[PathRef]] = Task.Sources {
+      Seq(PathRef(this.millSourcePath / os.up / "src" / env.debugOrRelease() / "java"))
     }
   }
 
diff --git a/hail/mill b/hail/mill
new file mode 100755
index 00000000000..f4d81f4419f
--- /dev/null
+++ b/hail/mill
@@ -0,0 +1,67 @@
+#!/usr/bin/env sh
+
+# This is a wrapper script, that automatically download mill from GitHub release pages
+# You can give the required mill version with MILL_VERSION env variable
+# If no version is given, it falls back to the value of DEFAULT_MILL_VERSION
+
+set -e
+
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then
+  DEFAULT_MILL_VERSION=0.12.3
+fi
+
+if [ -z "$MILL_VERSION" ] ; then
+  if [ -f ".mill-version" ] ; then
+    MILL_VERSION="$(tr '\r' '\n' < .mill-version | head -n 1 2> /dev/null)"
+  elif [ -f ".config/mill-version" ] ; then
+    MILL_VERSION="$(tr '\r' '\n' < .config/mill-version | head -n 1 2> /dev/null)"
+  elif [ -f "mill" ] && [ "$0" != "mill" ] ; then
+    MILL_VERSION=$(grep -F "DEFAULT_MILL_VERSION=" "mill" | head -n 1 | cut -d= -f2)
+  else
+    MILL_VERSION=$DEFAULT_MILL_VERSION
+  fi
+fi
+
+if [ "x${XDG_CACHE_HOME}" != "x" ] ; then
+  MILL_DOWNLOAD_PATH="${XDG_CACHE_HOME}/mill/download"
+else
+  MILL_DOWNLOAD_PATH="${HOME}/.cache/mill/download"
+fi
+MILL_EXEC_PATH="${MILL_DOWNLOAD_PATH}/${MILL_VERSION}"
+
+version_remainder="$MILL_VERSION"
+MILL_MAJOR_VERSION="${version_remainder%%.*}"; version_remainder="${version_remainder#*.}"
+MILL_MINOR_VERSION="${version_remainder%%.*}"; version_remainder="${version_remainder#*.}"
+
+if [ ! -s "$MILL_EXEC_PATH" ] ; then
+  mkdir -p "$MILL_DOWNLOAD_PATH"
+  if [ "$MILL_MAJOR_VERSION" -gt 0 ] || [ "$MILL_MINOR_VERSION" -ge 5 ] ; then
+    ASSEMBLY="-assembly"
+  fi
+  DOWNLOAD_FILE=$MILL_EXEC_PATH-tmp-download
+  MILL_VERSION_TAG=$(echo $MILL_VERSION | sed -E 's/([^-]+)(-M[0-9]+)?(-.*)?/\1\2/')
+  MILL_DOWNLOAD_URL="https://repo1.maven.org/maven2/com/lihaoyi/mill-dist/$MILL_VERSION/mill-dist-$MILL_VERSION.jar"
+  curl --fail -L -o "$DOWNLOAD_FILE" "$MILL_DOWNLOAD_URL"
+  chmod +x "$DOWNLOAD_FILE"
+  mv "$DOWNLOAD_FILE" "$MILL_EXEC_PATH"
+  unset DOWNLOAD_FILE
+  unset MILL_DOWNLOAD_URL
+fi
+
+if [ -z "$MILL_MAIN_CLI" ] ; then
+  MILL_MAIN_CLI="${0}"
+fi
+
+MILL_FIRST_ARG=""
+
+ # first arg is a long flag for "--interactive" or starts with "-i"
+if [ "$1" = "--bsp" ] || [ "${1#"-i"}" != "$1" ] || [ "$1" = "--interactive" ] || [ "$1" = "--no-server" ] || [ "$1" = "--repl" ] || [ "$1" = "--help" ] ; then
+  # Need to preserve the first position of those listed options
+  MILL_FIRST_ARG=$1
+  shift
+fi
+
+unset MILL_DOWNLOAD_PATH
+unset MILL_VERSION
+
+exec $MILL_EXEC_PATH $MILL_FIRST_ARG -D "mill.main.cli=${MILL_MAIN_CLI}" "$@"
diff --git a/hail/millw b/hail/millw
deleted file mode 100755
index 54154284d10..00000000000
--- a/hail/millw
+++ /dev/null
@@ -1,241 +0,0 @@
-#!/usr/bin/env sh
-
-# This is a wrapper script, that automatically download mill from GitHub release pages
-# You can give the required mill version with --mill-version parameter
-# If no version is given, it falls back to the value of DEFAULT_MILL_VERSION
-#
-# Project page: https://github.com/lefou/millw
-# Script Version: 0.4.11
-#
-# If you want to improve this script, please also contribute your changes back!
-#
-# Licensed under the Apache License, Version 2.0
-
-set -e
-
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then
-  DEFAULT_MILL_VERSION="0.11.6"
-fi
-
-
-if [ -z "${GITHUB_RELEASE_CDN}" ] ; then
-  GITHUB_RELEASE_CDN=""
-fi
-
-
-MILL_REPO_URL="https://github.com/com-lihaoyi/mill"
-
-if [ -z "${CURL_CMD}" ] ; then
-  CURL_CMD=curl
-fi
-
-# Explicit commandline argument takes precedence over all other methods
-if [ "$1" = "--mill-version" ] ; then
-  shift
-  if [ "x$1" != "x" ] ; then
-    MILL_VERSION="$1"
-    shift
-  else
-    echo "You specified --mill-version without a version." 1>&2
-    echo "Please provide a version that matches one provided on" 1>&2
-    echo "${MILL_REPO_URL}/releases" 1>&2
-    false
-  fi
-fi
-
-# Please note, that if a MILL_VERSION is already set in the environment,
-# We reuse it's value and skip searching for a value.
-
-# If not already set, read .mill-version file
-if [ -z "${MILL_VERSION}" ] ; then
-  if [ -f ".mill-version" ] ; then
-    MILL_VERSION="$(head -n 1 .mill-version 2> /dev/null)"
-  elif [ -f ".config/mill-version" ] ; then
-    MILL_VERSION="$(head -n 1 .config/mill-version 2> /dev/null)"
-  fi
-fi
-
-MILL_USER_CACHE_DIR="${XDG_CACHE_HOME:-${HOME}/.cache}/mill"
-
-if [ -z "${MILL_DOWNLOAD_PATH}" ] ; then
-  MILL_DOWNLOAD_PATH="${MILL_USER_CACHE_DIR}/download"
-fi
-
-# If not already set, try to fetch newest from Github
-if [ -z "${MILL_VERSION}" ] ; then
-  # TODO: try to load latest version from release page
-  echo "No mill version specified." 1>&2
-  echo "You should provide a version via '.mill-version' file or --mill-version option." 1>&2
-
-  mkdir -p "${MILL_DOWNLOAD_PATH}"
-  LANG=C touch -d '1 hour ago' "${MILL_DOWNLOAD_PATH}/.expire_latest" 2>/dev/null || (
-    # we might be on OSX or BSD which don't have -d option for touch
-    # but probably a -A [-][[hh]mm]SS
-    touch "${MILL_DOWNLOAD_PATH}/.expire_latest"; touch -A -010000 "${MILL_DOWNLOAD_PATH}/.expire_latest"
-  ) || (
-    # in case we still failed, we retry the first touch command with the intention
-    # to show the (previously suppressed) error message
-    LANG=C touch -d '1 hour ago' "${MILL_DOWNLOAD_PATH}/.expire_latest"
-  )
-
-  # POSIX shell variant of bash's -nt operator, see https://unix.stackexchange.com/a/449744/6993
-  # if [ "${MILL_DOWNLOAD_PATH}/.latest" -nt "${MILL_DOWNLOAD_PATH}/.expire_latest" ] ; then
-  if [ -n "$(find -L "${MILL_DOWNLOAD_PATH}/.latest" -prune -newer "${MILL_DOWNLOAD_PATH}/.expire_latest")" ]; then
-    # we know a current latest version
-    MILL_VERSION=$(head -n 1 "${MILL_DOWNLOAD_PATH}"/.latest 2> /dev/null)
-  fi
-
-  if [ -z "${MILL_VERSION}" ] ; then
-    # we don't know a current latest version
-    echo "Retrieving latest mill version ..." 1>&2
-    LANG=C ${CURL_CMD} -s -i -f -I ${MILL_REPO_URL}/releases/latest 2> /dev/null  | grep --ignore-case Location: | sed s'/^.*tag\///' | tr -d '\r\n' > "${MILL_DOWNLOAD_PATH}/.latest"
-    MILL_VERSION=$(head -n 1 "${MILL_DOWNLOAD_PATH}"/.latest 2> /dev/null)
-  fi
-
-  if [ -z "${MILL_VERSION}" ] ; then
-    # Last resort
-    MILL_VERSION="${DEFAULT_MILL_VERSION}"
-    echo "Falling back to hardcoded mill version ${MILL_VERSION}" 1>&2
-  else
-    echo "Using mill version ${MILL_VERSION}" 1>&2
-  fi
-fi
-
-MILL="${MILL_DOWNLOAD_PATH}/${MILL_VERSION}"
-
-try_to_use_system_mill() {
-  if [ "$(uname)" != "Linux" ]; then
-    return 0
-  fi
-
-  MILL_IN_PATH="$(command -v mill || true)"
-
-  if [ -z "${MILL_IN_PATH}" ]; then
-    return 0
-  fi
-
-  SYSTEM_MILL_FIRST_TWO_BYTES=$(head --bytes=2 "${MILL_IN_PATH}")
-  if [ "${SYSTEM_MILL_FIRST_TWO_BYTES}" = "#!" ]; then
-	  # MILL_IN_PATH is (very likely) a shell script and not the mill
-	  # executable, ignore it.
-	  return 0
-  fi
-
-  SYSTEM_MILL_PATH=$(readlink -e "${MILL_IN_PATH}")
-  SYSTEM_MILL_SIZE=$(stat --format=%s "${SYSTEM_MILL_PATH}")
-  SYSTEM_MILL_MTIME=$(stat --format=%y "${SYSTEM_MILL_PATH}")
-
-  if [ ! -d "${MILL_USER_CACHE_DIR}" ]; then
-    mkdir -p "${MILL_USER_CACHE_DIR}"
-  fi
-
-  SYSTEM_MILL_INFO_FILE="${MILL_USER_CACHE_DIR}/system-mill-info"
-  if [ -f "${SYSTEM_MILL_INFO_FILE}" ]; then
-    parseSystemMillInfo() {
-        LINE_NUMBER="${1}"
-        # Select the line number of the SYSTEM_MILL_INFO_FILE, cut the
-        # variable definition in that line in two halves and return
-        # the value, and finally remove the quotes.
-        sed -n "${LINE_NUMBER}p" "${SYSTEM_MILL_INFO_FILE}" |\
-            cut -d= -f2 |\
-            sed 's/"\(.*\)"/\1/'
-    }
-
-    CACHED_SYSTEM_MILL_PATH=$(parseSystemMillInfo 1)
-    CACHED_SYSTEM_MILL_VERSION=$(parseSystemMillInfo 2)
-    CACHED_SYSTEM_MILL_SIZE=$(parseSystemMillInfo 3)
-    CACHED_SYSTEM_MILL_MTIME=$(parseSystemMillInfo 4)
-
-    if [ "${SYSTEM_MILL_PATH}" = "${CACHED_SYSTEM_MILL_PATH}" ] \
-           && [ "${SYSTEM_MILL_SIZE}" = "${CACHED_SYSTEM_MILL_SIZE}" ] \
-           && [ "${SYSTEM_MILL_MTIME}" = "${CACHED_SYSTEM_MILL_MTIME}" ]; then
-      if [ "${CACHED_SYSTEM_MILL_VERSION}" = "${MILL_VERSION}" ]; then
-          MILL="${SYSTEM_MILL_PATH}"
-          return 0
-      else
-          return 0
-      fi
-    fi
-  fi
-
-  SYSTEM_MILL_VERSION=$(${SYSTEM_MILL_PATH} --version | head -n1 | sed -n 's/^Mill.*version \(.*\)/\1/p')
-
-  cat <<EOF > "${SYSTEM_MILL_INFO_FILE}"
-CACHED_SYSTEM_MILL_PATH="${SYSTEM_MILL_PATH}"
-CACHED_SYSTEM_MILL_VERSION="${SYSTEM_MILL_VERSION}"
-CACHED_SYSTEM_MILL_SIZE="${SYSTEM_MILL_SIZE}"
-CACHED_SYSTEM_MILL_MTIME="${SYSTEM_MILL_MTIME}"
-EOF
-
-  if [ "${SYSTEM_MILL_VERSION}" = "${MILL_VERSION}" ]; then
-    MILL="${SYSTEM_MILL_PATH}"
-  fi
-}
-try_to_use_system_mill
-
-# If not already downloaded, download it
-if [ ! -s "${MILL}" ] ; then
-
-  # support old non-XDG download dir
-  MILL_OLD_DOWNLOAD_PATH="${HOME}/.mill/download"
-  OLD_MILL="${MILL_OLD_DOWNLOAD_PATH}/${MILL_VERSION}"
-  if [ -x "${OLD_MILL}" ] ; then
-    MILL="${OLD_MILL}"
-  else
-    case $MILL_VERSION in
-      0.0.* | 0.1.* | 0.2.* | 0.3.* | 0.4.* )
-        DOWNLOAD_SUFFIX=""
-        DOWNLOAD_FROM_MAVEN=0
-        ;;
-      0.5.* | 0.6.* | 0.7.* | 0.8.* | 0.9.* | 0.10.* | 0.11.0-M* )
-        DOWNLOAD_SUFFIX="-assembly"
-        DOWNLOAD_FROM_MAVEN=0
-        ;;
-      *)
-        DOWNLOAD_SUFFIX="-assembly"
-        DOWNLOAD_FROM_MAVEN=1
-        ;;
-    esac
-
-    DOWNLOAD_FILE=$(mktemp mill.XXXXXX)
-
-    if [ "$DOWNLOAD_FROM_MAVEN" = "1" ] ; then
-      DOWNLOAD_URL="https://repo1.maven.org/maven2/com/lihaoyi/mill-dist/${MILL_VERSION}/mill-dist-${MILL_VERSION}.jar"
-    else
-      MILL_VERSION_TAG=$(echo "$MILL_VERSION" | sed -E 's/([^-]+)(-M[0-9]+)?(-.*)?/\1\2/')
-      DOWNLOAD_URL="${GITHUB_RELEASE_CDN}${MILL_REPO_URL}/releases/download/${MILL_VERSION_TAG}/${MILL_VERSION}${DOWNLOAD_SUFFIX}"
-      unset MILL_VERSION_TAG
-    fi
-
-    # TODO: handle command not found
-    echo "Downloading mill ${MILL_VERSION} from ${DOWNLOAD_URL} ..." 1>&2
-    ${CURL_CMD} -f -L -o "${DOWNLOAD_FILE}" "${DOWNLOAD_URL}"
-    chmod +x "${DOWNLOAD_FILE}"
-    mkdir -p "${MILL_DOWNLOAD_PATH}"
-    mv "${DOWNLOAD_FILE}" "${MILL}"
-
-    unset DOWNLOAD_FILE
-    unset DOWNLOAD_SUFFIX
-  fi
-fi
-
-if [ -z "$MILL_MAIN_CLI" ] ; then
-  MILL_MAIN_CLI="${0}"
-fi
-
-MILL_FIRST_ARG=""
-if [ "$1" = "--bsp" ] || [ "$1" = "-i" ] || [ "$1" = "--interactive" ] || [ "$1" = "--no-server" ] || [ "$1" = "--repl" ] || [ "$1" = "--help" ] ; then
-  # Need to preserve the first position of those listed options
-  MILL_FIRST_ARG=$1
-  shift
-fi
-
-unset MILL_DOWNLOAD_PATH
-unset MILL_OLD_DOWNLOAD_PATH
-unset OLD_MILL
-unset MILL_VERSION
-unset MILL_REPO_URL
-
-# We don't quote MILL_FIRST_ARG on purpose, so we can expand the empty value without quotes
-# shellcheck disable=SC2086
-exec "${MILL}" $MILL_FIRST_ARG -D "mill.main.cli=${MILL_MAIN_CLI}" "$@"
diff --git a/hail/src/main/scala/is/hail/expr/ir/Env.scala b/hail/src/main/scala/is/hail/expr/ir/Env.scala
index 8280bac16d5..adf9845376c 100644
--- a/hail/src/main/scala/is/hail/expr/ir/Env.scala
+++ b/hail/src/main/scala/is/hail/expr/ir/Env.scala
@@ -244,7 +244,7 @@ final class Env[V] private (val m: Map[Env.K, V]) {
     this(Map())
 
   override def equals(other: Any): Boolean = other match {
-    case env: Env[V] => this.m == env.m
+    case env: Env[_] => this.m == env.m
     case _ => false
   }
 
diff --git a/hail/src/main/scala/is/hail/expr/ir/RefEquality.scala b/hail/src/main/scala/is/hail/expr/ir/RefEquality.scala
index 0551e0b2191..bc6077ec480 100644
--- a/hail/src/main/scala/is/hail/expr/ir/RefEquality.scala
+++ b/hail/src/main/scala/is/hail/expr/ir/RefEquality.scala
@@ -10,7 +10,7 @@ object RefEquality {
 
 class RefEquality[+T <: AnyRef](val t: T) {
   override def equals(obj: scala.Any): Boolean = obj match {
-    case r: RefEquality[T] => t.eq(r.t)
+    case r: RefEquality[_] => t.eq(r.t)
     case _ => false
   }
 
diff --git a/hail/src/main/scala/is/hail/linalg/BlockMatrix.scala b/hail/src/main/scala/is/hail/linalg/BlockMatrix.scala
index 25328be4c11..7cda148db27 100644
--- a/hail/src/main/scala/is/hail/linalg/BlockMatrix.scala
+++ b/hail/src/main/scala/is/hail/linalg/BlockMatrix.scala
@@ -27,7 +27,7 @@ import breeze.stats.distributions.RandBasis
 import org.apache.commons.lang3.StringUtils
 import org.apache.spark._
 import org.apache.spark.executor.InputMetrics
-import org.apache.spark.mllib.linalg.distributed._
+import org.apache.spark.mllib.linalg.distributed.{GridPartitioner => _, _}
 import org.apache.spark.rdd.RDD
 import org.apache.spark.storage.StorageLevel
 import org.json4s._
diff --git a/hail/src/main/scala/is/hail/lir/SplitMethod.scala b/hail/src/main/scala/is/hail/lir/SplitMethod.scala
index 533f094bf7c..d19ad900f1a 100644
--- a/hail/src/main/scala/is/hail/lir/SplitMethod.scala
+++ b/hail/src/main/scala/is/hail/lir/SplitMethod.scala
@@ -1,6 +1,6 @@
 package is.hail.lir
 
-import is.hail.asm4s._
+import is.hail.asm4s.{classInfo, BooleanInfo, IntInfo, UnitInfo}
 import is.hail.utils._
 
 import scala.collection.mutable
diff --git a/hail/src/main/scala/is/hail/lir/X.scala b/hail/src/main/scala/is/hail/lir/X.scala
index 8b1f8739860..12406b367f2 100644
--- a/hail/src/main/scala/is/hail/lir/X.scala
+++ b/hail/src/main/scala/is/hail/lir/X.scala
@@ -1,6 +1,8 @@
 package is.hail.lir
 
-import is.hail.asm4s._
+import is.hail.asm4s.{
+  arrayInfo, ByteInfo, ClassInfo, DoubleInfo, FloatInfo, IntInfo, LongInfo, TypeInfo,
+}
 import is.hail.utils._
 
 import scala.collection.mutable
diff --git a/hail/src/test/scala/is/hail/asm4s/ASM4SSuite.scala b/hail/src/test/scala/is/hail/asm4s/ASM4SSuite.scala
index ceb3bee5bf4..3e4602f05e8 100644
--- a/hail/src/test/scala/is/hail/asm4s/ASM4SSuite.scala
+++ b/hail/src/test/scala/is/hail/asm4s/ASM4SSuite.scala
@@ -14,7 +14,7 @@ import org.testng.annotations.Test
 trait Z2Z { def apply(z: Boolean): Boolean }
 
 class ASM4SSuite extends HailSuite {
-  private[this] val theHailClassLoader = new HailClassLoader(getClass().getClassLoader())
+  override val theHailClassLoader = new HailClassLoader(getClass().getClassLoader())
 
   @Test def not(): Unit = {
     val notb = FunctionBuilder[Z2Z](