I have two different versions ("branches", but in fact only copies) of the same project open. I wanted to manually merge a change I did in one version to the other copy. So I selected all in the file I modified in project copy A, copied to clipboard, then switched to the same file in project B selected all again and invoked "Compare with Clipboard". Idea showed my changes just fine. At first I wondered that there are no icons to transfer each change, but then I realized that the file wasn't already checked out. I tried to make a dummy change (i.e. pressed enter) in the file, but nothing happened. Note: When I "compare two files" Idea does not show the merge icons either, but as soon as I press "enter" (or make any other change) Idea asks to check out the file and as soon as the checkout is complete, it shows all the merge symbols.