Handle unhandledRejections, help with cache eacces

[isaacs]

Suggested by @godmar in
https://npm.community/t/npm-err-cb-never-called-permission-denied/9167/5

Incidentally, this turned up that we're catching uncaughtExceptions in
the main npm functions, but not unhandledRejections!

Tracing this through, it seems like node-fetch-npm's use of cacache is
particularly brittle. Any throw that comes from cacache is not caught
properly, since node-fetch-npm is all streams and callbacks. The naive
approach (just adding a catch and failing the callback) doesn't work,
because then make-fetch-happen and npm-registry-fetch interpret the
failure as an invalid response, when actually it was a local cache
error.

So, a bit more love and polish is definitely still needed in the
guts of npm's fetching and caching code paths. In the meantime, though,
handling any unhandledRejection at the top level prevents at least the
worst and most useless type of error message.

[godmar]

This doesn't make a difference. The default handler for unhandledRejection throws and ends up in errorHandler anyway.

[isaacs]

This doesn't make a difference. The default handler for unhandledRejection throws and ends up in errorHandler anyway.

It does make a difference. The default handler for unhandledRejection crashes the process, but doesn't trigger the uncaughtException handler.

The difference in practice:

$ for i in $(grep -rl abbrev ~/.npm/_cacache); do d=$(dirname $i); sudo rm -f $i; sudo chown root $d; done

$ nave use 12

$ npm i abbrev
Unhandled rejection Error: EACCES: permission denied, rename '/Users/isaacs/.npm/_cacache/tmp/32202678' -> '/Users/isaacs/.npm/_cacache/content-v2/sha512/96/4d/01bc757c3d62aca07c6dc8267b18225dbfe06b168898c7b0e747e600f548fffa14e0d3ff896f0381dda4bb659b48197752436f1c9ad9db9e9082fc0000da'

npm ERR! cb() never called!

npm ERR! This is an error with npm itself. Please report this error at:
npm ERR!     <https://npm.community>

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/isaacs/.npm/_logs/2019-08-02T20_52_53_019Z-debug.log

$ exit

$ npm i abbrev
npm ERR! code EACCES
npm ERR! syscall rename
npm ERR! path /Users/isaacs/.npm/_cacache/tmp/778626ef
npm ERR! dest /Users/isaacs/.npm/_cacache/content-v2/sha512/96/4d/01bc757c3d62aca07c6dc8267b18225dbfe06b168898c7b0e747e600f548fffa14e0d3ff896f0381dda4bb659b48197752436f1c9ad9db9e9082fc0000da
npm ERR! errno -13
npm ERR!
npm ERR! Your cache folder contains root-owned files, due to a bug in
npm ERR! previous versions of npm which has since been addressed.
npm ERR!
npm ERR! To permanently fix this problem, please run:
npm ERR!   sudo chown -R 501:20 "/Users/isaacs/.npm"

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/isaacs/.npm/_logs/2019-08-02T20_52_57_589Z-debug.log

Without the explicit process.on('unhandledRejection'), the errorHandler method never gets executed.

[godmar]

I had noticed the lack of unhandledRejection when debugging this myself. You're right that in order to execute your errorHandler, you have to set it. It hadn't made a difference for me with the old error handler - in both case, you got a stack trace.

[isaacs]

It hadn't made a difference for me with the old error handler - in both case, you got a stack trace.

Right, the other bit of the fix is in lib/util/error-message