Silence node-sass output on success

[tlucas]

Environment

OS: Debian

• npm @ 5.6.0
• node @ v8.11.1
• adblockpluschrome @ 8f44d27 (git) 5039d6d02b4c (hg)

Background

In #6309, we started using node-sass for bundling CSS styles in adblockplusui.
After fixing postinstall-dependencies in #6488 (first occurrence of this behavior), node-sass writes a rendering-completed-message to stderr:

Rendering Complete, saving .css file...
Wrote CSS to /home/tlucas/abp/gitrepo/adblockpluschrome/adblockplusui/skin/desktop-options.css

While this behavior was reproduced in the aforementioned environment,
it causes the Cron Daemon on abp-builds-1 (the buildserver) to dispatch an email, every time adblockpluschrome is rebuilt:

Subject: Cron <devbuilds@abp-builds-1> python -m sitescripts.extensions.bin.createNightlies 
Message:

Rendering Complete, saving .css file...
Wrote CSS to /tmp/abpchromeLxGrxR/adblockplusui/skin/desktop-options.css
Rendering Complete, saving .css file...
Wrote CSS to /tmp/abpfirefoxyn05v5/adblockplusui/skin/desktop-options.css

While it's valuable to be informed about errors happening while automatically building the extension, IMHO it is of no value to receive a rather meaningless "done"-email from cron.

What to change

Let node-sass only write to stderr when an actual errors happens, in order to not dispatch any unnecessary email from inside a cron-job on abp-builds-1.

[tlucas]

According to ​https://www.npmjs.com/package/node-sass , section "options", passing -q or --quiet should be the solution.

[agiammarchi]

to be honest, I actually like while watching in development logs to see things are happening.

can we solve this using some environment variable instead of always disabling the sass output?

[greiner]

The issue appears to be that node-sass is writing this info message to stderr instead of stdout for whatever reason. Presumably, it does that because it wants to send the output to stdout if the --output flag is omitted.

[agiammarchi]

Replying to greiner:

node-sass is writing this info message to stderr instead of stdout for whatever reason.

sounds like a bug to me (a node-sass one)

Presumably, it does that because it wants to send the output to stdout if the --output flag is omitted.

outputting properly sounds good to me

[tlucas]

Replying to agiammarchi:

Replying to greiner:

node-sass is writing this info message to stderr instead of stdout for whatever reason.

sounds like a bug to me (a node-sass one)

Presumably, it does that because it wants to send the output to stdout if the --output flag is omitted.

outputting properly sounds good to me

Ah yes, my bad - changed the description accordingly.
How it's done in detail is up to the dev tackling this i guess - as long as nothing's printed to stderr, when no error happens ;)

[greiner]

What about adding a wrapper script for calling node-sass (e.g. build/sass.js) so that we can forward its output to the appropriate channel?

Because the only option I could find that'd allow us to keep using the CLI is to use the --error-bell flag to differentiate errors in the output but I'd consider that to be quite a workaround.

[tlucas]

We won't handle this on our side, instead ops will filter out the messages -> see ​http://hub.eyeo.com/issues/10639

[vedantydv123]

spam