This happened to me when I updated my Eclipse on MacOS.
You may simply reinstall Eclipse to have it work, but there is another solution to it.
The reason is that the eclipse.ini does not have the correct path to the launcher after updates. So, first open eclipse.ini by right click the application eclipse, then "show package content". Edit eclipse.ini such that
launcher.library points to the new path as in "plugins/org.eclipse.equinox.launcher.carbon.*"
You may also change the -startup by setting it to a new .jar file.
Save it and now your eclipe is back to normal again!