Problem

You want to compile and/or run different test or binary targets using different JVMs.

Or, you need to specify command-line options globally for the JVM on a per-JVM version basis. For example, using --add-opens flags, but only when running on JVMs that support it.

Solution

In your global configuration (most likely pants.toml), declare JVM platforms using the jvm-platform configuration section to define the set of available platforms.

On targets, add the named argument runtime_platform set to the name of one of the platforms defined in jvm-platform. That will tell pants to use that platform when running that target in a JVM.

runtime_platform="java8",

To compile with a specific platform, set the platform on the target.

platform="java8",

To set the defaults for platform and runtime_platform, add default_platform and default_runtime_platform to your global config.

Discussion

Here are the different configurations that you can set when defining a JVM platform in your global configuration.

For compile time configuration, there are three main attributes, source, target and args. * source and target map directly to the javac arguments of the same name, though they accept more aliases than javac. Up to JDK 8, you can use either 1.X or X. For 9 and up, you can't include the 1.. * args, allows the platform to specify additional, global to that platform, compile arguments.

For runtime configuration, target and jvm_options are used. target is used to determine the version of the JVM to use. jvm_options is used by some tasks to allow platforms to specify platform specific JVM options. These can make transitions between JVM versions smoother by allowing compatibility options to be provided globally.

An example pants.toml config might look like this:

[jvm-platform]
default_platform: java8
default_runtime_platform: java10
platforms =
"""
 {
    'java8': { 'source': '8', 'target': '8', 'args': [] },
    'java10': {'source': '10', 'target': '10', 'args': [],
               'jvm_options': [
                   # --add-opens is a 9+ flag, that doesn't work with 8
                   '--add-opens=java.base/java.lang.reflect=ALL-UNNAMED'
               ] },
  }

"""

See Also

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