On a Mac without a JDK, preparing failed with "Java 25 is needed ...
/usr/bin/javac -version printed no version: Unable to locate a Java
Runtime": /usr/bin/javac is macOS's placeholder. Mojang's Java runtimes
are whole JDKs, javac included (java-runtime-epsilon is 25.0.1 on every
platform), and the official launcher has already downloaded one for
anyone who played 26.3.
- horizon-prepare: java::find also tries Minecraft's runtimes
(<game dir>/runtime/<component>/<platform>/<component>, jre.bundle on
macOS) and the launcher's pick (Options::java_home), and names the
macOS placeholder for what it is.
- launcher: when no JDK is found, downloads the runtime the version JSON
names (javaVersion.component) from Mojang into its own game folder,
every file checked against its sha1, executables and links as the
official launcher lays them out. A version's own preparer binary or
Python script gets it through JAVA_HOME and the PATH.
Checked for real on Linux: the download is 147 files, its javac 25.0.1
compiles and runs a class with --release 25.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01AxbYUJt4ShJFCdyLNCxF21
