Handle EPIPE on stdout gracefully

[radhikalism]

Problem: when yarn outputs to a pipe, it is sensitive to the pipe closing prematurely. If the pipe is closed before output is finished, a noisy error message appears on stderr.

It appears all commands with reporter output are affected. (yarn help appears to be unaffected, for example.)

Expected: yarn should handle the broken stdout pipe error quietly and complete its work (and exit with whatever status it would have otherwise).

To reproduce: trivial examples on node versions 8.x through 11.x, using head to truncate output before the last line:

$ yarn versions | head -n 16
yarn versions v1.15.2
{ yarn: '1.16.0-0',
  http_parser: '2.8.0',
  node: '8.15.1',
  v8: '6.2.414.75',
  uv: '1.23.2',
...
  tz: '2017c' }
events.js:183
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.afterWrite [as oncomplete] (net.js:868:14)

$ yarn versions | head -n 16
yarn versions v1.15.2
{ yarn: '1.16.0-0',
  http_parser: '2.8.0',
  node: '9.11.2',
  v8: '6.2.414.46-node.23',
  uv: '1.19.2',
...
  tz: '2018c' }
events.js:165
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.afterWrite [as oncomplete] (net.js:844:14)
Emitted 'error' event at:
    at onwriteError (_stream_writable.js:431:12)
    at onwrite (_stream_writable.js:453:5)
    at _destroy (internal/streams/destroy.js:39:7)
    at Socket.stdout._destroy (internal/process/stdio.js:19:7)
    at Socket.destroy (internal/streams/destroy.js:32:8)
    at WriteWrap.afterWrite [as oncomplete] (net.js:846:10)

$ yarn versions | head -n 31
yarn versions v1.15.2
{ yarn:
   '1.16.0-0',
  http_parser:
   '2.8.0',
  node:
   '10.15.3',
  v8:
   '6.8.275.32-node.51',
  uv:
   '1.23.2',
...
  tz:
   '2018e' }
events.js:174
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.afterWrite [as oncomplete] (net.js:779:14)
Emitted 'error' event at:
    at onwriteError (_stream_writable.js:431:12)
    at onwrite (_stream_writable.js:456:5)
    at _destroy (internal/streams/destroy.js:40:7)
    at Socket.dummyDestroy [as _destroy] (internal/process/stdio.js:11:34)
    at Socket.destroy (internal/streams/destroy.js:32:8)
    at WriteWrap.afterWrite [as oncomplete] (net.js:781:10)

$ yarn versions | head -n 35
yarn versions v1.15.2
{ yarn:
   '1.16.0-0',
  node:
   '11.13.0',
  v8:
   '7.0.276.38-node.18',
  uv:
   '1.27.0',
...
  unicode:
   '11.0' }
events.js:170
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.onWriteComplete [as oncomplete] (internal/stream_base_commons.js:67:16)
Emitted 'error' event at:
    at errorOrDestroy (internal/streams/destroy.js:107:12)
    at onwriteError (_stream_writable.js:436:5)
    at onwrite (_stream_writable.js:461:5)
    at _destroy (internal/streams/destroy.js:49:7)
    at Socket.dummyDestroy [as _destroy] (internal/process/stdio.js:11:5)
    at Socket.destroy (internal/streams/destroy.js:37:8)
    at WriteWrap.onWriteComplete [as oncomplete] (internal/stream_base_commons.js:68:12)

For comparison, npm (on node v11.13.0) behaves as expected:

$ npm version | head -n 15
{ yarn: '1.16.0-0',
  npm: '6.7.0',
...
  uv: '1.27.0',
  v8: '7.0.276.38-node.18',

This PR demonstrates a possible fix, which swallows pipe and stream errors on stdout without taking action, allowing yarn to complete quietly and exit as it would otherwise.

The correct behavior is visible like this (on node v11.13.0) for example:

$ yarn-local versions | head -n 35
yarn versions v1.16.0-0
{ yarn:
   '1.16.0-0',
  node:
   '11.13.0',
  v8:
   '7.0.276.38-node.18',
  uv:
   '1.27.0',
...
  unicode:
   '11.0' }

Please discuss.

[buildsize]

File name	Previous Size	New Size	Change
yarn-[version].noarch.rpm	1.11 MB	1.11 MB	552 bytes (0%)
yarn-[version].js	4.48 MB	4.48 MB	233 bytes (0%)
yarn-legacy-[version].js	4.67 MB	4.67 MB	241 bytes (0%)
yarn-v[version].tar.gz	1.12 MB	1.12 MB	1.52 KB (0%)
yarn_[version]all.deb	816.87 KB	816.95 KB	84 bytes (0%)

[arcanis]

Seems reasonable 👍