I'm new to modding minecraft and I'm making a mod for 1.15.2. When I tried to update the MCP and type in 'gradlew genEclipseRuns' and 'gradlew eclipse' they both said build successful but referenced libraries don't appear which I believe is the reason why minecraft won't run. Here is a pastebin to the cmd output when I typed the two commands in https://pastebin.com/uCXq01Fi . If you need any other information please ask.
Fix: Just update your java installation, I updated both JDK and JRE at the same time so idk which one fixed it, but I recommend updating both anyways.