On IntelliJ IDEA 2016.3: it's hidden inside the cog button of the debug panel. Ensure Show Method Return Values
is checked.
Use the debugger to break somewhere inside the function whose return value you'd like to see.
Step out of the function (or step over until you escape):
Observe that the return value appears in your variables:
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…