Add ninja generator flag for writing library deps.

Add ninja generator flag for writing library deps.

This adds a flag to the ninja generator to specify a file to write library
deps to as generation proceeds. This is so GN can suck the deps out.

BUG=288991

[brettw, 2013-09-05 19:28:45]

I open the file for appending each time. I thought some portion of GYP was
multithreaded and this will definitely break if done in parallel from multiple
threads. Do you know if what I'm doing is OK, or suggest any better ideas?

[Nico, 2013-09-09 23:27:27]

I think this change is fine (minor comments below), but there should probably be
some "experiment with gn" bug that this CL should reference. For people who
don't know what GN is, the CL description is rather cryptic, so having a link to
a bug would be good.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:213: generator_flags, toplevel_dir=None):
It's nicer to not pass in the whole flags object, just the bits you need
(deps_file_name=None) and do the flags parsing where the NinjaWriters are
instantiated.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:253: self.link_deps_file =
open(generator_flags.get(LINK_DEPS_FILE), 'ab')
Do you want to empty the file before creating the first NinjaWriter? Else this
file will grow and grow every time gyp runs.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:991: self.link_deps_file.write(target.binary)
This isn't correct on windows if you want to use incremental linking. Not sure
if you care.

Note that target.binary can contain spaces. self.qualified_target won't so this
encoding is fine (but maybe surprising)

[Evan Martin, 2013-09-09 23:49:34]

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:255: self.link_deps_file = False
Why not "None" (also above in the comment), since it's still falsey and it makes
link_deps_file well-typed.

[brettw, 2013-09-10 21:12:13]

New snap up, PTAL.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:213: generator_flags, toplevel_dir=None):
On 2013/09/09 23:27:27, Nico wrote:
> It's nicer to not pass in the whole flags object, just the bits you need
> (deps_file_name=None) and do the flags parsing where the NinjaWriters are
> instantiated.

Done.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:253: self.link_deps_file =
open(generator_flags.get(LINK_DEPS_FILE), 'ab')
On 2013/09/09 23:27:27, Nico wrote:
> Do you want to empty the file before creating the first NinjaWriter? Else this
> file will grow and grow every time gyp runs.

I currently delete it from GN before doing the spawning. I guess I can add the
delete logic to GYP also, but that would be in a different file and it seemed
messy (since these are generator flags).

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:255: self.link_deps_file = False
On 2013/09/09 23:49:34, Evan Martin wrote:
> Why not "None" (also above in the comment), since it's still falsey and it
makes
> link_deps_file well-typed.

Good idea, done.

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:991: self.link_deps_file.write(target.binary)
On 2013/09/09 23:27:27, Nico wrote:
> This isn't correct on windows if you want to use incremental linking. Not sure
> if you care.

I'll worry about this later, I don't understand how it works now.
 
> Note that target.binary can contain spaces. self.qualified_target won't so
this
> encoding is fine (but maybe surprising)

Okay, I think my parser handles this currently so we should be OK.

[Nico, 2013-09-10 21:56:55]

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/23601020/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:253: self.link_deps_file =
open(generator_flags.get(LINK_DEPS_FILE), 'ab')
On 2013/09/10 21:12:13, brettw wrote:
> On 2013/09/09 23:27:27, Nico wrote:
> > Do you want to empty the file before creating the first NinjaWriter? Else
this
> > file will grow and grow every time gyp runs.
> 
> I currently delete it from GN before doing the spawning. I guess I can add the
> delete logic to GYP also, but that would be in a different file and it seemed
> messy (since these are generator flags).

Huh? Couldn't you create the file in GenerateOutputForConfig() at the bottom, i
guess even just once in 'wb' mode, and then pass in the file object to every
NinjaWriter?

[Nico, 2013-09-10 21:58:02]

https://codereview.chromium.org/23601020/diff/7001/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/23601020/diff/7001/pylib/gyp/generator/ninja....
pylib/gyp/generator/ninja.py:213: deps_file_name=None, toplevel_dir=None):
rename to deps_file

https://codereview.chromium.org/23601020/diff/7001/pylib/gyp/generator/ninja....
pylib/gyp/generator/ninja.py:254: self.link_deps_file = None
remove most of this, and just keep `self.link_deps_file = deps_file`

https://codereview.chromium.org/23601020/diff/7001/pylib/gyp/generator/ninja....
pylib/gyp/generator/ninja.py:2040: link_deps_file =
generator_flags.get(LINK_DEPS_FILE)
Do link_deps_file = open(gen…ILE), 'wb') here

[brettw, 2013-09-11 20:05:01]

I see, I didn't have the right picture of how it works. I moved the file open to
above the for loop and did the rest of your comments. This seems a lot better,
PTAL.

[Nico, 2013-09-11 20:06:00]

lgtm