[error when running]

i keep getting this error when running my mod, "Reference to undefined variable MC_VERSION". im running version 1.12.2 which i think i heard isn't supported here anymore but i'm still posting to see if i can get some help as i've looked and asked everywhere and just cannot find out how to fix this problem. would be incredible if someone could help, thank you.

[how to edit minecrafts files]

Hi, so im new to using forge for modding, but when i used mcp i was able to change the original minecraft folders. Basically i want to change the GuiButton, but im not able to edit any of the original minecraft files. On mcp i could just click on GuiButton.java and do what i wanteed with it, but now its GuiButton.class and im not able to edit it. Is there any way of editing this file, and any of the other mineraft files or no? If not is there any other way i can try to have custom gui buttons and what not.

[forge not working]

he uses intellij, im using eclipse, i dont think they work the same cause when i open my src, like he does in the begging, there is no build.gradle

[forge not working]

hey so im trying to make a mod, but i cant get into eclipse with forge. im following this tutorial - 

... at 12:17 he launches into eclipse folder. i do not have an eclipse folder even tough i have done everything he has done