Java runtime needed even if not using the JVM. Error message is not very helpful

[scuellar]

I'm running

% cabal run saw -w ghc-8.10   
Up to date
saw: user error (/usr/bin/java returned non-zero exit code: ExitFailure 1
Standard output:

Standard error:
The operation couldn’t be completed. Unable to locate a Java Runtime.
Please visit http://www.java.com for information on installing Java.


)

I'm not sure why I need java runtime. A better error message could be helpful.

[RyanGlScott]

Ouch, that is unfortunate. By default, if SAW cannot find a Java installation at startup, then it doesn't perform any additional work. But you are in a strange situation where you do have Java installed /usr/bin/java, but it returns an unexpected error code due to some sort of misconfiguration.

In any case, having SAW simply error out at startup when you're not using the JVM-related functionality is a pretty poor user experience. We should at least check to see if java returns non-zero exit code, and if so, convert the error above into a warning so that SAW can still proceed.

[scuellar]

In my case, all java was installed but not linked properly. For future reference use
brew info openjdk

Which informs you that you need to symlink it with

 sudo ln -sfn /usr/local/opt/openjdk/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk.jdk

That did the trick.

[sauclovian-g]

Given that this happens by default on macos, maybe we should add logic to try to check for that case and print something helpful.

[RyanGlScott]

Note that the issue really lies in crucible-jvm. Specifically, note the type of findJavaMajorVersion, which SAW calls when processing command-line options:

findJavaMajorVersion :: FilePath -> IO Int

This returns an Int, but in the event that invoking java fails, it will simply throw an exception. While we could catch the exception on the SAW side, it would be better to change the return type of findJavaMajorVersion to something like IO (Either Text Int) (where Left indicates a java failure) so that callers are explicitly forced to reckon with the case where java fails.