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Use symlinks instead of moving build directory #278

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Use symlinks instead of moving build directory
Malax Oct 21, 2025
9a26c75
Update CHANGELOG
Malax Oct 31, 2025
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

## [Unreleased]

* Use symlinks instead of moving the build directory. ([#278](https://github.com/heroku/heroku-buildpack-scala/pull/278))

## [v103] - 2025-10-27

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17 changes: 3 additions & 14 deletions bin/compile
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Expand Up @@ -34,22 +34,11 @@ metrics::setup

if is_app_dir "${APP_BUILD_DIR}"; then
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(for another PR) The function is called is_app_dir but it actually seems to checks for whether the directory is not the /app dir?

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@edmorley edmorley Oct 31, 2025 •
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I don't see a Heroku CI Hatchet test in this repo - and Heroku CI is one of the cases where the /app directory gets used instead of /tmp/build_* - would it be worth adding a Heroku CI test?

(The other case when the app dir varies is when the build-in-app-dir labs is enabled - I don't bother having a hatchet test for that for Python, but do make sure to test that labs manually when making any /app vs /tmp path-specific changes)

BUILD_DIR="/tmp/scala_buildpack_build_dir"
mv "${APP_BUILD_DIR}" "${BUILD_DIR}"
ln -s "${APP_BUILD_DIR}" "${BUILD_DIR}"
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(optional) I find these variable names confusing, given in most other buildpacks the BUILD_DIR really does mean the actual build dir. For example the rm "${BUILD_DIR}" later looks really bad until you know it's only the symlink!

I wonder if the symlink path should be named something else?

else
BUILD_DIR="${APP_BUILD_DIR}"
fi

# When multiple buildpacks are used, earlier buildpacks may add executables to PATH
# and GEM_PATH that reference APP_BUILD_DIR. Since we've moved the build directory to
# a temp location, we must rewrite these environment variables to replace APP_BUILD_DIR
# with the new BUILD_DIR so that executables added by earlier buildpacks remain accessible.
PATH=${PATH//"${APP_BUILD_DIR}"/"${BUILD_DIR}"}
export PATH
if [[ -n "${GEM_PATH:-}" ]]; then
GEM_PATH=${GEM_PATH//"${APP_BUILD_DIR}"/"${BUILD_DIR}"}
export GEM_PATH
fi

util::export_env_dir "${ENV_DIR}" "." "JAVA_OPTS"

# Used by openjdk::install_openjdk_via_jvm_common_buildpack to determine which JVM common buildpack to use
Expand Down Expand Up @@ -277,9 +266,9 @@ cat <<-EOF >"${profile_script}"
export PATH="\$SBT_HOME/bin:\$PATH"
EOF

# Move compiled app back to where Heroku expects it
# Remove symlink if we created one
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(background only) For Python and PHP we don't remove the symlinks after, in case later buildpacks happen to call those paths. I imagine that's less likely to happen for Scala though.

if is_app_dir "${APP_BUILD_DIR}"; then
mv "${BUILD_DIR}" "${APP_BUILD_DIR}"
rm "${BUILD_DIR}"
fi

# write export script
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76 changes: 38 additions & 38 deletions test/spec/cache_spec.rb
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Expand Up @@ -13,21 +13,21 @@
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/scala_buildpack_build_dir/.sbt_home/launchers/1.11.7/sbt-launch.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/scala_buildpack_build_dir/.sbt_home/launchers/1.11.7/sbt-launch.jar.md5
remote: /tmp/scala_buildpack_build_dir/.sbt_home/launchers/1.11.7/sbt-launch.jar: OK
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/scala_buildpack_build_dir/.sbt_home/plugins
remote: \\[info\\] compiling 1 Scala source to /tmp/scala_buildpack_build_dir/.sbt_home/plugins/target/scala-2.12/sbt-1.0/classes ...
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\\] Non-compiled module 'compiler-bridge_2.12' for Scala 2.12.20. Compiling...
remote: \\[info\\] Compilation completed in .*s.
remote: \\[info\\] done compiling
remote: \\[info\\] loading settings for project scala_buildpack_build_dir-build from plugins.sbt...
remote: \\[info\\] loading project definition from /tmp/scala_buildpack_build_dir/project
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...
remote: \\[info\\] __ __
remote: \\[info\\] \\\\ \\\\ ____ / /____ _ __ __
Expand All @@ -42,10 +42,10 @@
remote: \\[info\\] https://www.playframework.com/sponsors
remote: \\[info\\]
remote: \\[info\\] Executing in batch mode. For better performance use sbt's shell
remote: \\[info\\] compiling 7 Scala sources and 1 Java source to /tmp/scala_buildpack_build_dir/target/scala-2.13/classes ...
remote: \\[info\\] compiling 7 Scala sources and 1 Java source to /tmp/[^/]+/target/scala-2.13/classes ...
remote: \\[info\\] done compiling
remote: \\[success\\] Total time: .* s, completed .*
remote: \\[info\\] Wrote /tmp/scala_buildpack_build_dir/target/scala-2.13/sbt-0-11-7-play-3-x-scala-2-13-x_2.13-1.0-SNAPSHOT.pom
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
Expand All @@ -68,9 +68,9 @@
remote: -----> Installing Azul Zulu OpenJDK 21.0.[0-9]+
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/scala_buildpack_build_dir/.sbt_home/plugins
remote: \\[info\\] loading settings for project scala_buildpack_build_dir-build from plugins.sbt...
remote: \\[info\\] loading project definition from /tmp/scala_buildpack_build_dir/project
remote: \\[info\\] loading global plugins from /tmp/[^/]+/.sbt_home/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...
remote: \\[info\\] __ __
remote: \\[info\\] \\\\ \\\\ ____ / /____ _ __ __
Expand All @@ -86,7 +86,7 @@
remote: \\[info\\]
remote: \\[info\\] Executing in batch mode. For better performance use sbt's shell
remote: \\[success\\] Total time: .* s, completed .*
remote: \\[info\\] Wrote /tmp/scala_buildpack_build_dir/target/scala-2.13/sbt-0-11-7-play-3-x-scala-2-13-x_2.13-1.0-SNAPSHOT.pom
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
Expand Down Expand Up @@ -131,7 +131,7 @@
remote: -----> Running: sbt compile stage
remote: Downloading sbt launcher for 0.13.9:
remote: From https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/sbt-launch/0.13.9/sbt-launch.jar
remote: To /tmp/scala_buildpack_build_dir/.sbt_home/launchers/0.13.9/sbt-launch.jar
remote: To /tmp/[^\\s]+/.sbt_home/launchers/0.13.9/sbt-launch.jar
remote:
remote: Getting org.scala-sbt sbt 0.13.9 ...
remote: downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/sbt/0.13.9/jars/sbt.jar ...
Expand Down Expand Up @@ -253,8 +253,8 @@
remote: :: retrieving :: org.scala-sbt#boot-scala
remote: confs: \\[default\\]
remote: 5 artifacts copied, 0 already retrieved \\(24493kB/[0-9]+ms\\)
remote: \\[info\\] Loading global plugins from /tmp/scala_buildpack_build_dir/.sbt_home/plugins
remote: \\[info\\] Updating \\{file:/tmp/scala_buildpack_build_dir/.sbt_home/plugins/\\}global-plugins...
remote: \\[info\\] Loading global plugins from /tmp/[^\\s]+/.sbt_home/plugins
remote: \\[info\\] Updating \\{file:/tmp/[^\\s]+/.sbt_home/plugins/\\}global-plugins...
remote: \\[info\\] Resolving org.scala-lang#scala-library;2.10.5 ...
remote: \\[info\\] Resolving org.scala-sbt#sbt;0.13.9 ...
remote: \\[info\\] Resolving org.scala-sbt#main;0.13.9 ...
Expand Down Expand Up @@ -311,9 +311,9 @@
remote: \\[info\\] Resolving org.scala-lang#jline;2.10.5 ...
remote: \\[info\\] Resolving org.fusesource.jansi#jansi;1.4 ...
remote: \\[info\\] Done updating.
remote: \\[info\\] Compiling 1 Scala source to /tmp/scala_buildpack_build_dir/.sbt_home/plugins/target/scala-2.10/sbt-0.13/classes...
remote: \\[info\\] Loading project definition from /tmp/scala_buildpack_build_dir/project
remote: \\[info\\] Updating \\{file:/tmp/scala_buildpack_build_dir/project/\\}scala_buildpack_build_dir-build...
remote: \\[info\\] Compiling 1 Scala source to /tmp/[^\\s]+/.sbt_home/plugins/target/scala-2.10/sbt-0.13/classes...
remote: \\[info\\] Loading project definition from /tmp/[^\\s]+/project
remote: \\[info\\] Updating \\{file:/tmp/[^\\s]+/project/\\}[^\\s]+-build...
remote: \\[info\\] Resolving org.scala-sbt#global-plugins;0.0 ...
remote: \\[info\\] Resolving com.typesafe.play#sbt-plugin;2.4.2 ...
remote: \\[info\\] Resolving com.typesafe.play#sbt-plugin;2.4.2 ...
Expand Down Expand Up @@ -833,8 +833,8 @@
remote: \\[info\\] downloading https://jcenter.bintray.com/org/webjars/npm/2.11.2/npm-2.11.2.jar ...
remote: \\[info\\] \\[SUCCESSFUL \\] org.webjars#npm;2.11.2!npm.jar \\([0-9]+ms\\)
remote: \\[info\\] Done updating.
remote: \\[info\\] Set current project to play-2.4.x-scala \\(in build file:/tmp/scala_buildpack_build_dir/\\)
remote: \\[info\\] Updating \\{file:/tmp/scala_buildpack_build_dir/\\}root...
remote: \\[info\\] Set current project to play-2.4.x-scala \\(in build file:/tmp/[^\\s]+/\\)
remote: \\[info\\] Updating \\{file:/tmp/[^\\s]+/\\}root...
remote: \\[info\\] Resolving org.scala-lang#scala-compiler;2.11.6 ...
remote: \\[info\\] Resolving org.scala-lang#scala-compiler;2.11.6 ...
remote: \\[info\\] Resolving org.scala-lang#scala-library;2.11.6 ...
Expand Down Expand Up @@ -1359,16 +1359,16 @@
remote: \\[info\\] downloading https://jcenter.bintray.com/jline/jline/2.12.1/jline-2.12.1.jar ...
remote: \\[info\\] \\[SUCCESSFUL \\] jline#jline;2.12.1!jline.jar \\([0-9]+ms\\)
remote: \\[info\\] Done updating.
remote: \\[info\\] Compiling 7 Scala sources and 1 Java source to /tmp/scala_buildpack_build_dir/target/scala-2.11/classes...
remote: \\[info\\] Compiling 7 Scala sources and 1 Java source to /tmp/[^\\s]+/target/scala-2.11/classes...
remote: \\[info\\] 'compiler-interface' not yet compiled for Scala 2.11.6. Compiling...
remote: \\[info\\] Compilation completed in .*
remote: \\[success\\] Total time: .*, completed .*
remote: \\[info\\] Wrote /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.pom
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-web-assets.jar ...
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.jar ...
remote: \\[info\\] Wrote /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.pom
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-web-assets.jar ...
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.jar ...
remote: \\[info\\] Done packaging.
remote: \\[info\\] Done packaging.
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-sans-externalized.jar ...
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-sans-externalized.jar ...
remote: \\[info\\] Done packaging.
remote: \\[success\\] Total time: .*, completed .*
remote: -----> Collecting dependency information
Expand Down Expand Up @@ -1408,8 +1408,8 @@
remote: ! - https://www.scala-sbt.org/1.x/docs/Migrating-from-sbt-013x.html
remote:
remote: -----> Running: sbt compile stage
remote: \\[info\\] Loading global plugins from /tmp/scala_buildpack_build_dir/.sbt_home/plugins
remote: \\[info\\] Updating \\{file:/tmp/scala_buildpack_build_dir/.sbt_home/plugins/\\}global-plugins...
remote: \\[info\\] Loading global plugins from /tmp/[^\\s]+/.sbt_home/plugins
remote: \\[info\\] Updating \\{file:/tmp/[^\\s]+/.sbt_home/plugins/\\}global-plugins...
remote: \\[info\\] Resolving org.scala-lang#scala-library;2.10.5 ...
remote: \\[info\\] Resolving org.scala-sbt#sbt;0.13.9 ...
remote: \\[info\\] Resolving org.scala-sbt#main;0.13.9 ...
Expand Down Expand Up @@ -1466,9 +1466,9 @@
remote: \\[info\\] Resolving org.scala-lang#jline;2.10.5 ...
remote: \\[info\\] Resolving org.fusesource.jansi#jansi;1.4 ...
remote: \\[info\\] Done updating.
remote: \\[info\\] Compiling 1 Scala source to /tmp/scala_buildpack_build_dir/.sbt_home/plugins/target/scala-2.10/sbt-0.13/classes...
remote: \\[info\\] Loading project definition from /tmp/scala_buildpack_build_dir/project
remote: \\[info\\] Updating \\{file:/tmp/scala_buildpack_build_dir/project/\\}scala_buildpack_build_dir-build...
remote: \\[info\\] Compiling 1 Scala source to /tmp/[^\\s]+/.sbt_home/plugins/target/scala-2.10/sbt-0.13/classes...
remote: \\[info\\] Loading project definition from /tmp/[^\\s]+/project
remote: \\[info\\] Updating \\{file:/tmp/[^\\s]+/project/\\}[^\\s]+-build...
remote: \\[info\\] Resolving org.scala-sbt#global-plugins;0.0 ...
remote: \\[info\\] Resolving com.typesafe.play#sbt-plugin;2.4.2 ...
remote: \\[info\\] Resolving com.typesafe.play#routes-compiler_2.10;2.4.2 ...
Expand Down Expand Up @@ -1615,8 +1615,8 @@
remote: \\[info\\] Resolving org.scala-lang#jline;2.10.5 ...
remote: \\[info\\] Resolving org.fusesource.jansi#jansi;1.4 ...
remote: \\[info\\] Done updating.
remote: \\[info\\] Set current project to play-2.4.x-scala \\(in build file:/tmp/scala_buildpack_build_dir/\\)
remote: \\[info\\] Updating {file:/tmp/scala_buildpack_build_dir/}root...
remote: \\[info\\] Set current project to play-2.4.x-scala \\(in build file:/tmp/[^\\s]+/\\)
remote: \\[info\\] Updating {file:/tmp/[^\\s]+/}root...
remote: \\[info\\] Resolving org.scala-lang#scala-compiler;2.11.6 ...
remote: \\[info\\] Resolving org.scala-lang#scala-library;2.11.6 ...
remote: \\[info\\] Resolving org.scala-lang#scala-reflect;2.11.6 ...
Expand Down Expand Up @@ -1731,14 +1731,14 @@
remote: \\[info\\] Resolving org.ow2.asm#asm-util;4.1 ...
remote: \\[info\\] Resolving jline#jline;2.12.1 ...
remote: \\[info\\] Done updating.
remote: \\[info\\] Compiling 7 Scala sources and 1 Java source to /tmp/scala_buildpack_build_dir/target/scala-2.11/classes...
remote: \\[info\\] Compiling 7 Scala sources and 1 Java source to /tmp/[^\\s]+/target/scala-2.11/classes...
remote: \\[success\\] Total time: .*, completed .*
remote: \\[info\\] Wrote /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.pom
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-web-assets.jar ...
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.jar ...
remote: \\[info\\] Wrote /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.pom
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-web-assets.jar ...
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT.jar ...
remote: \\[info\\] Done packaging.
remote: \\[info\\] Done packaging.
remote: \\[info\\] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-sans-externalized.jar ...
remote: \\[info\\] Packaging /tmp/[^\\s]+/target/scala-2.11/play-2-4-x-scala_2.11-1.0-SNAPSHOT-sans-externalized.jar ...
remote: \\[info\\] Done packaging.
remote: \\[success\\] Total time: .*, completed .*
remote: -----> Collecting dependency information
Expand Down