Add CHANGELOG entry

Author: Malax

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+* Replace sbt-extras with direct sbt launcher installation. ([#291](https://github.com/heroku/heroku-buildpack-scala/pull/291))
 * Remove build directory symlinking. Modern sbt versions no longer require a stable build path for caching. ([#290](https://github.com/heroku/heroku-buildpack-scala/pull/290))
 
 ## [v103] - 2025-10-27

bin/compile

@@ -131,6 +131,15 @@ if has_old_preset_sbt_opts; then
 	EOF
 fi
 
+# Copy the target dir from cache to speed up compilation. This is legacy buildpack
+# behavior that other JVM buildpacks don't implement. It can cause cache bloat, stale artifacts,
+# and reduced build reproducibility. We've observed customers using SBT_CLEAN (which will remove these files)
+# much more than expected (~10% of builds), presumably to work around issues.
+# This will be removed in a future version.
+target_dir_cache_restore_start_time=$(util::nowms)
+util::cache_copy "target" "${CACHE_DIR}" "${BUILD_DIR}"
+metrics::set_duration "target_dir_cache_restore_duration" "${target_dir_cache_restore_start_time}"
+
 if [[ -n "${SBT_PROJECT}" ]]; then
 	SBT_TASKS="${SBT_PROJECT}/compile ${SBT_PROJECT}/stage"
 else
@@ -147,8 +156,6 @@ fi
 # See: https://devcenter.heroku.com/articles/scala-support#clean-builds
 [[ "${SBT_CLEAN}" = "true" ]] && SBT_TASKS="clean ${SBT_TASKS}"
 
-
-
 ivy_home_dir="${CACHE_DIR}/ivy_home"
 util::prepend_to_env "SBT_OPTS" "-Dsbt.ivy.home=${ivy_home_dir}"
 mkdir -p "${ivy_home_dir}"
@@ -161,24 +168,35 @@ sbt_boot_dir="${CACHE_DIR}/sbt_boot"
 util::prepend_to_env "SBT_OPTS" "-Dsbt.boot.directory=${sbt_boot_dir}"
 mkdir -p "${sbt_boot_dir}"
 
-# Recreate the sbt global directory on each build with the current Heroku plugins and settings.
 # See: https://www.scala-sbt.org/1.x/docs/Command-Line-Reference.html
 sbt_global_dir="${CACHE_DIR}/sbt_global"
 util::prepend_to_env "SBT_OPTS" "-Dsbt.global.base=${sbt_global_dir}"
-rm -rf "${sbt_global_dir}"
 mkdir -p "${sbt_global_dir}"
 
-# Install the Heroku sbt plugin
-mkdir -p "${sbt_global_dir}/plugins"
+# Install the Heroku sbt plugin if the exising version differs (or is missing). We do this conditionally to
+# ensure we can cache the compiled class files of the plugin between builds, speeding up the build overall.
 case "${sbt_version}" in
 1.*)
-	cp "${BUILDPACK_DIR}/opt/HerokuBuildpackPlugin_sbt1.scala" "${sbt_global_dir}/plugins/HerokuBuildpackPlugin.scala"
+	plugin_source_path="${BUILDPACK_DIR}/opt/HerokuBuildpackPlugin_sbt1.scala"
 	;;
 *)
-	cp "${BUILDPACK_DIR}/opt/HerokuBuildpackPlugin.scala" "${sbt_global_dir}/plugins/HerokuBuildpackPlugin.scala"
+	plugin_source_path="${BUILDPACK_DIR}/opt/HerokuBuildpackPlugin.scala"
 	;;
 esac
 
+plugins_dir="${sbt_global_dir}/plugins"
+plugin_destination_path="${plugins_dir}/HerokuBuildpackPlugin.scala"
+source_checksum="$(sha256sum "${plugin_source_path}" | awk '{print $1}')"
+
+if [[ ! -f "${plugin_destination_path}" ]] || [[ "${source_checksum}" != "$(sha256sum "${plugin_destination_path}" | awk '{print $1}')" ]]; then
+	# We remove the whole directory since we also want to remove the (cached) compiled files
+	# for the older version of the plugin in the ./target directory.
+	rm -rf "${plugins_dir}"
+
+	mkdir -p "${plugins_dir}"
+	cp "${plugin_source_path}" "${plugin_destination_path}"
+fi
+
 sbt::install_sbt_launcher "${sbt_version}" "${CACHE_DIR}/sbt-launcher"
 
 # Collect metrics
@@ -196,36 +214,39 @@ fi
 
 # build app
 cd "${BUILD_DIR}"
+
 run_sbt "${SBT_TASKS}"
 
 if [[ -z "${DISABLE_DEPENDENCY_CLASSPATH_LOG:-}" ]]; then
 	write_sbt_dependency_classpath_log
 fi
 
-# drop useless directories from slug for play and sbt-native-launcher only
-if is_sbt_native_packager "${BUILD_DIR}" || is_play "${BUILD_DIR}"; then
-	if [[ "${KEEP_SBT_CACHE:-}" != "true" ]]; then
-		if [[ -d "${BUILD_DIR}/target" ]]; then
-			output::step "Dropping compilation artifacts from the slug"
-			rm -rf "${BUILD_DIR}/target/scala-"*
-			rm -rf "${BUILD_DIR}/target/streams"
-			if [[ -d "${BUILD_DIR}/target/resolution-cache" ]]; then
-				find "${BUILD_DIR}/target/resolution-cache"/* ! -name "reports" ! -name "*-compile.xml" -print0 | xargs -0 rm -rf --
-			fi
-		fi
-	fi
+# Copy the target dir back to cache for the next build (see cache restore comment above for context)
+target_dir_cache_write_start_time=$(util::nowms)
+util::cache_copy "target" "${BUILD_DIR}" "${CACHE_DIR}"
+metrics::set_duration "target_dir_cache_write_duration" "${target_dir_cache_write_start_time}"
+
+# When sbt-native-packager is used (either directly or implicitly by the Play framework), a standalone JAR file with
+# all code and dependencies is created. This makes the other JAR and class files redundant since they are not used by
+# the running application. We remove these files here to reduce the slug size. However, this is a broad assumption that
+# is often but not always correct. Users might want to use these files to run the application differently or for other
+# purposes. This is legacy behavior that we will not change at this point to avoid users running into slug size limits
+# needlessly. Ideally customers would curate their builds to not include extraneous files.
+if (is_sbt_native_packager "${BUILD_DIR}" || is_play "${BUILD_DIR}") && [[ "${KEEP_SBT_CACHE:-}" != "true" ]]; then
+	output::step "Dropping compilation artifacts from the slug"
+	rm -rf "${BUILD_DIR}/target/scala-"*
+	rm -rf "${BUILD_DIR}/target/streams"
+	find "${BUILD_DIR}/target/resolution-cache" -mindepth 1 ! -name "reports" ! -name "*-compile.xml" -exec rm -rf {} + 2>/dev/null || true
 fi
 
 # write profile.d script
 profile_script="${BUILD_DIR}/.profile.d/scala.sh"
 mkdir -p "$(dirname "${profile_script}")"
 cat <<-EOF >"${profile_script}"
-	export SBT_HOME="\$HOME/${SBT_USER_HOME}"
 	export PATH="\$SBT_HOME/bin:\$PATH"
 EOF
 
 # write export script
 cat <<-EOF >"${BASE_DIR}/export"
-	export SBT_HOME="${BUILD_DIR}/${SBT_USER_HOME}"
 	export PATH="\$SBT_HOME/bin:\$PATH"
 EOF

lib/sbt.sh

@@ -21,7 +21,7 @@ function sbt::install_sbt_launcher() {
 	cat <<-EOF >"${sbt_launcher_dir}/bin/sbt"
 		#!/usr/bin/env bash
 		script_dir="\$(cd "\$(dirname "\${BASH_SOURCE[0]}")" && pwd)"
-		java -jar "\${script_dir}/../sbt-launch-${sbt_version}.jar" "\$@"
+		java \${SBT_OPTS:-} -jar "\${script_dir}/../sbt-launch-${sbt_version}.jar" "\$@"
 	EOF
 
 	chmod +x "${sbt_launcher_dir}/bin/sbt"
@@ -99,7 +99,7 @@ function sbt::download_sbt_launcher_jar() {
 	local sha1_path
 	sha1_path=$(mktemp)
 
-	if ! curl --silent --show-error --location "${sbt_launcher_jar_url}.sha1" > "${sha1_path}" 2>/dev/null; then
+	if ! curl --silent --show-error --location "${sbt_launcher_jar_url}.sha1" >"${sha1_path}" 2>/dev/null; then
 		output::error <<-EOF
 			Error: Unable to download SHA-1 checksum for sbt launcher.
 		EOF

test/spec/cache_spec.rb

@@ -10,19 +10,14 @@
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
           remote: -----> Scala app detected
           remote: -----> Installing Azul Zulu OpenJDK 21.0.[0-9]+
+          remote: -----> Downloading sbt launcher 1.11.7...
+          remote: -----> Setting up sbt launcher...
           remote: -----> Running: sbt compile stage
-          remote: Downloading sbt launcher for 1.11.7:
-          remote:   From  https://repo1.maven.org/maven2/org/scala-sbt/sbt-launch/1.11.7/sbt-launch-1.11.7.jar
-          remote:     To  /tmp/[^/]+/.sbt_home/launchers/1.11.7/sbt-launch.jar
-          remote: Downloading sbt launcher 1.11.7 md5 hash:
-          remote:   From  https://repo1.maven.org/maven2/org/scala-sbt/sbt-launch/1.11.7/sbt-launch-1.11.7.jar.md5
-          remote:     To  /tmp/[^/]+/.sbt_home/launchers/1.11.7/sbt-launch.jar.md5
-          remote:        /tmp/[^/]+/.sbt_home/launchers/1.11.7/sbt-launch.jar: OK
           remote: \\[info\\] \\[launcher\\] getting org.scala-sbt sbt 1.11.7  \\(this may take some time\\)...
           remote: \\[info\\] \\[launcher\\] getting Scala 2.12.20 \\(for sbt\\)...
           remote:        \\[info\\] welcome to sbt 1.11.7 \\(Azul Systems, Inc. Java 21.0.[0-9]+\\)
-          remote:        \\[info\\] loading global plugins from /tmp/[^/]+/.sbt_home/plugins
-          remote:        \\[info\\] compiling 1 Scala source to /tmp/[^/]+/.sbt_home/plugins/target/scala-2.12/sbt-1.0/classes ...
+          remote:        \\[info\\] loading global plugins from .*/plugins
+          remote:        \\[info\\] compiling 1 Scala source to .* ...
           remote:        \\[info\\] Non-compiled module 'compiler-bridge_2.12' for Scala 2.12.20. Compiling...
           remote:        \\[info\\]   Compilation completed in .*s.
           remote:        \\[info\\] done compiling
@@ -48,9 +43,6 @@
           remote:        \\[info\\] Wrote /tmp/[^/]+/target/scala-2.13/sbt-0-11-7-play-3-x-scala-2-13-x_2.13-1.0-SNAPSHOT.pom
           remote:        \\[success\\] Total time: .*
           remote: -----> Collecting dependency information
-          remote: -----> Dropping ivy cache from the slug
-          remote: -----> Dropping sbt boot dir from the slug
-          remote: -----> Dropping sbt cache dir from the slug
           remote: -----> Dropping compilation artifacts from the slug
           remote: -----> Discovering process types
           remote:        Procfile declares types     -> \\(none\\)
@@ -66,9 +58,10 @@
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
           remote: -----> Scala app detected
           remote: -----> Installing Azul Zulu OpenJDK 21.0.[0-9]+
+          remote: -----> Setting up sbt launcher...
           remote: -----> Running: sbt compile stage
           remote:        \\[info\\] welcome to sbt 1.11.7 \\(Azul Systems, Inc. Java 21.0.[0-9]+\\)
-          remote:        \\[info\\] loading global plugins from /tmp/[^/]+/.sbt_home/plugins
+          remote:        \\[info\\] loading global plugins from .*/plugins
           remote:        \\[info\\] loading settings for project [^\\s]+-build from plugins.sbt...
           remote:        \\[info\\] loading project definition from /tmp/[^/]+/project
           remote:        \\[info\\] loading settings for project root from build.sbt...
@@ -89,9 +82,6 @@
           remote:        \\[info\\] Wrote /tmp/[^/]+/target/scala-2.13/sbt-0-11-7-play-3-x-scala-2-13-x_2.13-1.0-SNAPSHOT.pom
           remote:        \\[success\\] Total time: .*
           remote: -----> Collecting dependency information
-          remote: -----> Dropping ivy cache from the slug
-          remote: -----> Dropping sbt boot dir from the slug
-          remote: -----> Dropping sbt cache dir from the slug
           remote: -----> Dropping compilation artifacts from the slug
           remote: -----> Discovering process types
           remote:        Procfile declares types     -> \\(none\\)