eclipse: Let IDE compile into a different directory than target/

[vorburger]

Following up on #340 (and my various PRs related to that), I'm still regularly hitting another Eclipse IDE related problem when working on this project: Having both the IDE and a CLI Terminal for mvn open, one gets those annoying "conflicts" when Eclipse (M2E) seems to Build at the wrong time and interfere with a Maven build running on the CLI. For example, I've just hit the problem below, which of course makes no sense at all, and goes away after I disable Project > Build Automatically and then rebuild on the CLI:

[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ jetcd-core ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 22 source files to /home/vorburger/dev/ODL/git.etcd/jetcd/jetcd-core/target/test-classes
[INFO] Some messages have been simplified; recompile with -Xdiags:verbose to get full output
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] /home/vorburger/dev/ODL/git.etcd/jetcd/jetcd-core/src/test/java/io/etcd/jetcd/internal/impl/AuthClientTest.java:[113,9] cannot access Permission.Type
  class file for Permission.Type not found
[ERROR] /home/vorburger/dev/ODL/git.etcd/jetcd/jetcd-core/src/test/java/io/etcd/jetcd/internal/impl/AuthClientTest.java:[116,88] incompatible types: io.etcd.jetcd.auth.Permission.Type cannot be converted to Permission.Type
[INFO] 2 errors 

But one should not have to manually work around this of course, this isn't productive. In other projects I have worked on, I've solved this by configuring Eclipse (via a change to a projects POM) to use target-ide/ instead of target/, so that the two build environments don't step onto each others foot.

If there is no objection, I'll raise a PR which proposes the same for this project as well.

PS: Some days I wonder if we shouldn't have a better global parent POM for this - @fbricon ?

[vorburger]

https://github.com/opendaylight/odlparent/blob/1032b37a4b10784c709ce1c2a060ec80db3e6ba1/odlparent-lite/pom.xml#L324

[fbricon]

this is the right solution for this problem. As for having a global parent pom.xml? YMMV. Some projects using hot-reload benefit from having the build output shared between the IDE and CLI.
For a local development workflow requiring regular CLI builds, I think skipping the clean part of the build is usually acceptable and doesn't cause problems. Because you're not actually performing production deployment from your machine, are you? ;-)

[vorburger]

Good hint re. clean, tx. I just don't trust mvn anymore without clean. 😉