Bootstrapping Gradle, Kotlin, a JDK and Scala from source with Nix

Goal: build recent Gradle, Kotlin and Scala without any prebuilt JDK, Kotlin, Scala, Gradle, IntelliJ or Maven-Central binaries, starting from the (bootstrappable) Nix stdenv.

Layout

Path	What
flake.nix	pinned nixpkgs, exposes everything as legacyPackages
nix/default.nix	the scope tying the stages together (jdk8/jdk11/jdk21 come from nix/jdk; gradleFor instantiates a Gradle version)
nix/jdk/	the JDK chain: jikes → GNU Classpath/JamVM → ecj → IcedTea 7 → OpenJDK 8 … 21 (jdks.openjdkNN); Guix-derived recipes for 9, 10 and 12–20
nix/lib/mk-jar.nix	mkJar: compile a source tree with javac into a jar (like Guix' ant-build-system #:jar-name)
nix/lib/fetch-*.nix	source fetchers that strip shipped binaries (*.jar, *.class, …)
nix/java/	Ant, ANTLR (2 … tunnelvisionlabs 4.7.4), ICU data, Groovy 3.0.5, protobuf and ~30 third party Java libraries, from source
nix/intellij/	IntelliJ SDK modules (util, core, jps-model, javac2, …) for SDKs 139 … 193, 201+
nix/kotlin/	the Kotlin chain 0.6.786 → 1.1 → 1.2 → 1.3 → … → 2.4.0
nix/gradle/	Gradle 9.8.0 and 8.14.3: ~80 third party libs, Groovy 4.0.33/3.0.24, Kotlin plugins/embeddable jars, every Gradle module compiled directly by javac/kotlinc, distribution assembly
nix/scala/	the Scala chain (2004 Java scalac → 1.x → nsc → 2.13.18, and dotty → 3.10.0)
scala/	the Scala chain records (chain/), stage builders, their tools and tests, and the prototype that found the stages; see scala/README.md
patches/tarcv/	patches from TarCV/kotlin-guix (Apache-2.0)
patches/guix/	patches from Guix for the JDK, ANTLR and Groovy recipes
patches/own/	our patches: IntelliJ SDK ports, Ant runtime targets for Kotlin 1.1.x–1.4
patches/scala/	the hooks of the Scala generations and the scripts of the bridge stages
tools/	hash prefetch/fix helpers, module-graph extraction (gradle-modules, kotlin-modules, intellij-modules), the generators of the Scala chains' Nix files (scala-chain, dotty-nix)

Usage

nix build .#jdks.openjdk21                  # JDK 21, from jikes up
nix build .#kotlin."0.6.786"                # first Kotlin stage, pure Java
nix build .#kotlin."2.4.0"                  # Kotlin 2.4.0 (many stages later)
nix build .#gradleDist                      # Gradle 9.8.0 (= .#gradle."9.8.0".dist)
nix build .#gradle."8.14.3".dist            # Gradle 8.14.3
nix build .#scala.\"2.13.18\"                # Scala 2.13.18, from the 2004 Java scalac
nix build .#scala.\"3.10.0\"                 # Scala 3.10.0 (= .#scala.latest)

Smoke test of the Gradle build: JAVA_HOME=$(nix build --no-link --print-out-paths .#jdks.openjdk21) result/bin/gradle --offline --no-daemon build

Status

See NOTES.md for the detailed log.

• JDK: built entirely from source. nix/jdk provides OpenJDK 8–21, boot-strapped from jikes + GNU Classpath + JamVM → ecj → IcedTea 7 (nixpkgs' OpenJDK recipe is reused for 8, 11, 17 and 21, fed with our own boot JDK). jdk8, jdk11 and jdk21 in nix/default.nix all point into this chain; no temurin seed is used.
• Kotlin: 0.6.786 → 2.4.0, every version compiled by the previous one (Ant-based up to 1.2.x, then module-wise kotlinc/javac). Built and smoke-tested up to 2.4.0 (K2 enabled from 2.1.0). Note kotlin.latest is still 1.1.2-5; use kotlin."2.4.0".
• Gradle: 9.8.0 and 8.14.3 distributions build and run (Groovy and Kotlin DSL java/application builds, offline, --no-daemon). Not done: AWS/GCS/maven modules (resources-s3, resources-gcs, build-init), JNI libraries, and Scala compilation (the Zinc worker is stubbed).
• Scala: 2.13.18 and 3.10.0. A chain of scala/scala commits (Java scalac of 2004 → Scala 1.x → nsc → 2.x, the first stage translated from Pizza to Java by scala/tools/pizza2java.py), each stage compiled by the previous one, reaches 2.13.18; from 2.12.8 a chain of scala/scala3 commits, each built by the reference compiler it names, reaches 3.10.0. The MSIL backend is stubbed; jline, jansi, scala-asm, zinc's interfaces and the other Java inputs are built from source.
• Ant, all Java dependencies, IntelliJ SDK modules: built from source.
• ICU's data (icudata.jar, used by icu4j to generate ANTLR 4's Unicode tables) is rebuilt from the Unicode Character Database text files (nix/java/icu); the prebuilt data in ICU's sources is deleted at fetch time.

Credits

The bootstrap path for Kotlin 1.1.2-5 is the work of Emmanuel Bourg (ebourg/kotlin-bootstrapping), Julien Lepiller (guix-android) and TarCV (kotlin-guix). This repository ports it to Nix.