jvms switch clobbers JAVA_HOME and fails with cryptic "symlink ... : The system cannot find the path specified" when java_home is unset

[sebyku]

Summary

When java_home is empty in the config (e.g. jvms init was never run), jvms switch <ver> produces a misleading error and destructively overwrites the machine JAVA_HOME to an empty string before failing.

Steps to reproduce

1. Fresh setup, place jvms.exe, run jvms install 25 (do not run jvms init).
2. In an elevated shell: jvms switch 25.

Actual result

Switch jdk failed, symlink C:\Program Files\jvms\store\25 : The system cannot find the path specified.

The version is correctly installed (jvms list shows it; store\25 contains a valid JDK). The empty gap between store\25 and : is the missing link target. Before this error, setx JAVA_HOME "" /M has already run, wiping any previously-set machine JAVA_HOME.

Root cause (internal/cmdCli/switch.go)

config.JavaHome is "". switchFunc then:

• runs setx JAVA_HOME "" /M (treated as success), then
• calls os.Symlink(filepath.Join(config.Store, v), config.JavaHome) with an empty newname, which Windows rejects.

There is no guard that config.JavaHome is non-empty. Confirmed via %APPDATA%\jvms\jvms.json: "java_home": "".

Suggested fix

• Early in switchFunc (and init), if config.JavaHome == "", return a clear error: "JAVA_HOME location not configured — run jvms init [--java_home <path>] first."
• Do not run setx JAVA_HOME ... /M until the target is validated, so a failed switch can't clear an existing JAVA_HOME.

Environment

• jvms v2.1.14, default new branch index
• Windows 11 Pro (10.0.26200), x64