The /execute command will execute said command at the executors location instead of at the specified entity's location.

For example, running the following

/execute @e[type=bat] ~ ~ ~ testfor @p[r=2]

in a command block will only give a successful output if you are within a radius of 2 blocks from the command block, as opposed to from the bat.

Here are some video examples where the bat is told to explode (via summoned creeper) with a successful output:
Previous/Expected Behavior (1.12-pre1): https://youtu.be/05ALD44QtaU
Current Behavior (1.12-pre2): https://youtu.be/En6l4UmK1rg
(The commands themselves used in the example videos are consistent and listed in either video's description.)