Support for MAVEN_OPTS

[gnodet]

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It would make sense to support the MAVEN_OPTS environment variable. See https://github.com/apache/maven-mvnd/issues/567

[ppalaga]

Two caveats come to my mind:

• I use both mvn and mvnd and I might want to have less Xmx for mvn than for mvnd will I be able to reach that?
• Precendence between MAVEN_OPTS and mvnd.jvmArgs: would one replace the other? Or would we try to merge both before passing the args to java?

[Stephan202]

Two-cents drive-by comment: generally more specific settings should override more general settings. System properties are more specific than environment variables, since the former are per-JVM, while an environment can contain multiple JVMs. Similarly, between on-disk properties and environment properties I would say that the latter should take precedence, since the latter can be specificed per-process, while the former apply to all processes.

I.e., in order from highest to lower precedence:

• The mvnd.jvmArgs system property.
• The MAVEN_OPTS environment property.
• The mvnd.properties properties file.

Afaik most software follows these rules. Examples include Spring and the AWS SDK.