Configs Blimp Engine official build to use non-debug build with dcheck_always_on

build/args/bots/official.desktop/blimp-engine.gn

 import("//build/args/blimp_engine.gn")
-is_debug = true
+is_debug = false
+dcheck_always_on = true

[maniscalco, 2016/04/29 18:32:28]

Why change the flags here instead of in build/args/blimp_engine.gn ?  What's the
rationale?

[haibinlu, 2016/04/29 22:51:34]

in local development case, debug build is desirable. 

[maniscalco, 2016/04/29 22:58:57]

For local builds we always have the option of just adding is_debug = true to our
args.gn file (just like we do with use_goma = true).

Dirk, WDYT?  Should we be adding the new args to
//build/args/bots/official.desktop/blimp-engine.gn or
//build/args/blimp_engine.gn ?

[Dirk Pranke, 2016/04/30 00:04:32]

Well, the //build/args/bots file needs to transitively include the
flags that the builder needs. However, if you just stuff them 
all in //build/args/blimp_engine.gn, then blimp_engine isn't
really all that different from the .../bots file and so you
might as well get rid of it.

So, that suggests that args/blimp_engine should be different
in at least some way. One approach would be to only have 
that file contain the flags that will be the same for *any*
engine build, so that would ban is_debug, 
is_component_build, etc. And then devs would add stuff 
as needed to customize for default, release, shared, etc.

Another approach would be to do what is done here, 
and leave args/blimp_engine as just the default dev 
build (in this case, debug, maybe also should be shared 
and not static?).

A third would be to create the 'base blimp mixin' file, 
and then additional templates as needed
for a dev debug build, a dev release build, the actual 
bot build, etc.

This is basically the same question I wrestled with
in the MB config (//tools/mb/mb_config.pyl). 
I don't really know what the right way to expose this 
tuff is, so I'd suggest you pick whatever makes 
your team happiest.

[maniscalco, 2016/05/02 19:13:00]

Dirk, that's helpful thanks.

SGTM.  I can see value in having the two different configurations
(//build/args/bots and //build/args/blimp_engine.gn).

I'm OK with putting is_debug and dcheck_always_on in the bots file.

Haibin, can you add a comment to //build/args/blimp_engine.gn that tells the
reader which build args belong in the file?  E.g.

# This file contains Blimp engine build args common to both
# official builds and personal development builds.

Also, can you add a comment in the bots file about why we want is_debug = false,
but DCHECKs on (improve engine performance, but notice bugs).