Hi there... I'm getting compilation errors on a Nano for a Neopixel program that has not changed and compiled successfully yesterday. Other programs compile just fine. Happening on desktop version of the Arduino program running on Mac, as well as the Web one. Error below:
arduino-builder/arduino-builder -compile -core-api-version 10611 -build-path /tmp/908358496 -hardware arduino-builder/hardware -hardware arduino-builder/packages/cores -tools arduino-builder/tools -tools arduino-builder/packages/tools -built-in-libraries arduino-builder/latest -libraries /tmp/595493061/pinned -libraries /tmp/595493061/custom -fqbn arduino:avr:nano:cpu=atmega328 -build-cache /tmp -verbose=false /tmp/595493061/sketch_aug24a
Multiple libraries were found for "Adafruit_NeoPixel.h"
Used: /tmp/595493061/custom/Adafruit_NeoPixel-master
Not used: /home/admin/builder/arduino-builder/latest/Adafruit NeoPixel-1.1.2
/tmp/ccLtBZLK.ltrans0.ltrans.o: In function `main':
/home/admin/builder/arduino-builder/packages/cores/arduino/avr/cores/arduino/main.cpp:46: undefined reference to `loop'
collect2: error: ld returned 1 exit status
exit status 1
Sounds like you may have imported an errant lib.
Try killing that one and letting it use the inbuilt one.
That would be my first step.
Anybody know how to "kill an errant lib"?
I haven't downloaded anything new, library wise, and as I said, nothing changed on my end between it working and not. 
The Library Manager only shows one copy. Where would the other one be?
Furthermore, this new problem also happens with the web-based Arduino Create, where I (presumeably) have no control over the libraries. Same exact error.
Someone tinkered with some code and broke something, right here:
/home/admin/builder/arduino-builder/packages/cores/arduino/avr/cores/arduino/main.cpp:46: undefined reference to `loop'
In fact, other nearly identical sketches for the very same Nano and neoPixel strip compile just fine, with reference to the exact same library. The only difference I can see is the use of floating point math in the one that won't compile.
Please provide a link to the bad sketch on CREATE (use the share option).
Luckily I am currently playing with WS8212's so its easy for me to test and check a few things.
Here's the one that is failing:
Oh brother, wow, am I an idiot. I now see the problem
No loop
D'oh
So obviously I --did-- change something, namely that I made the edit to change the big 'loop' into a function that I was then going to embed into another program. And then forgot that I did that. And of course the clue was right there in the thing I was point at as being something someone had changed on the server side. D'oh.
Sorry for wasting everybody's time. 
No problem and thanks for being up front about it.
Funny how I can look at a thing 100 times, and then the first time I look at it after I've sent it to someone else, I suddenly see the issue. Am I really looking at it with"new eyes" as I imagine you looking at it for the first time, and if so, why can't I just do that for my self one of the first 99 times! 
Thanks so much for taking the time to offer advice!