In case it helps, here the log file mentioned above (but I think it pretty much echoes stdout)
!SESSION 2018-10-15 13:17:29.132 -----------------------------------------------
eclipse.buildId=4.8.0.I20180611-0500
java.version=1.8.0_151
java.vendor=Oracle Corporation
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Command-line arguments: -os linux -ws gtk -arch x86_64 -product org.eclipse.epp.package.java.product -application org.eclipse.equinox.p2.director -repository
http://dist.springsource.org/release/GRECLIPSE/e4.7 -installIU org.codehaus.groovy.eclipse.feature.feature.group
!ENTRY org.eclipse.equinox.p2.director 4 10054 2018-10-15 13:17:32.278
!MESSAGE Cannot complete the install because of a conflicting dependency.
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.278
!MESSAGE Software being installed: Eclipse Groovy Development Tools 3.0.0.xx-201808021626-e47-RELEASE (org.codehaus.groovy.eclipse.feature.feature.group 3.0.0.xx-201808021626-e47-RELEASE)
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.278
!MESSAGE Software currently installed: Eclipse Java Development Tools 3.14.0.v20180611-0500 (org.eclipse.jdt.feature.group 3.14.0.v20180611-0500)
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.278
!MESSAGE Only one of the following can be installed at once:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.278
!MESSAGE Java Development Tools Core 3.14.0.v20180528-0519 (org.eclipse.jdt.core 3.14.0.v20180528-0519)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE Java Development Tools Core 3.13.102.xx-201808021626-e47-RELEASE (org.eclipse.jdt.core 3.13.102.xx-201808021626-e47-RELEASE)
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From: Groovy-Eclipse Compilerless Feature 3.0.0.xx-201808021626-e47-RELEASE (org.codehaus.groovy.compilerless.feature.feature.group 3.0.0.xx-201808021626-e47-RELEASE)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: org.eclipse.equinox.p2.iu; org.codehaus.groovy.headless.feature.feature.group [3.0.0.xx-201808021626-e47-RELEASE,3.0.0.xx-201808021626-e47-RELEASE]
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From: Eclipse Groovy Development Tools 3.0.0.xx-201808021626-e47-RELEASE (org.codehaus.groovy.eclipse.feature.feature.group 3.0.0.xx-201808021626-e47-RELEASE)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: org.eclipse.equinox.p2.iu; org.codehaus.groovy.compilerless.feature.feature.group [3.0.0.xx-201808021626-e47-RELEASE,3.0.0.xx-201808021626-e47-RELEASE]
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From: Groovy-Eclipse Headless Feature 3.0.0.xx-201808021626-e47-RELEASE (org.codehaus.groovy.headless.feature.feature.group 3.0.0.xx-201808021626-e47-RELEASE)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: org.eclipse.equinox.p2.iu; org.codehaus.groovy.jdt.patch.feature.group [3.0.0.xx-201808021626-e47-RELEASE,3.0.0.xx-201808021626-e47-RELEASE]
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From: Java Annotation Processing UI 3.6.0.v20180417-0931 (org.eclipse.jdt.apt.ui 3.6.0.v20180417-0931)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: osgi.bundle; org.eclipse.jdt.core [3.14.0,4.0.0)
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From: Eclipse Java Development Tools 3.14.0.v20180611-0500 (org.eclipse.jdt.feature.group 3.14.0.v20180611-0500)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: org.eclipse.equinox.p2.iu; org.eclipse.jdt.apt.ui [3.6.0.v20180417-0931,3.6.0.v20180417-0931]
!SUBENTRY 1 org.eclipse.equinox.p2.director 4 1 2018-10-15 13:17:32.279
!MESSAGE Cannot satisfy dependency:
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE From Patch: org.codehaus.groovy.jdt.patch.feature.group 3.0.0.xx-201808021626-e47-RELEASE Eclipse Java Development Tools 3.14.0.v20180611-0500 (org.eclipse.jdt.feature.group 3.14.0.v20180611-0500)
!SUBENTRY 2 org.eclipse.equinox.p2.director 4 0 2018-10-15 13:17:32.279
!MESSAGE To: org.eclipse.equinox.p2.iu; org.eclipse.jdt.core [3.13.102.xx-201808021626-e47-RELEASE,3.13.102.xx-201808021626-e47-RELEASE]