[GN] Add deployment target in generated project.

[GN] Add deployment target in generated project.

If deployment target is not specified, Xcode defaults to the most
recent SDK and prevent running the application on a device running
an older version.

This CL change the XcodeWriter object to build a scope from all
declared arguments (with declared_args) and override the them with
the values from build arguments (in $output_dir/args.gn). Before
that, XcodeWriter only looked at build arguments and returned wrong
values (i.e. most of the time the Value from build arguments was
not set and the default value was returned).

BUG=619072

[sdefresne, 2016-06-14 17:40:55]

Description was changed from

==========
[GN] Add deployment target in generated project.

If deployment target is not specified, Xcode defaults to the most
recent SDK and prevent running the application on a device running
an older version.

This CL change the XcodeWriter object to build a scope from all
declared arguments (with declared_args) and override the them with
the values from build arguments (in $output_dir/args.gn). Before
that, XcodeWriter only looked at build arguments and returned wrong
values (i.e. most of the time the Value from build arguments was
not set and the default value was returned).

BUG=619072
==========

to

==========
[GN] Add deployment target in generated project.

If deployment target is not specified, Xcode defaults to the most
recent SDK and prevent running the application on a device running
an older version.

This CL change the XcodeWriter object to build a scope from all
declared arguments (with declared_args) and override the them with
the values from build arguments (in $output_dir/args.gn). Before
that, XcodeWriter only looked at build arguments and returned wrong
values (i.e. most of the time the Value from build arguments was
not set and the default value was returned).

BUG=619072
==========

[sdefresne, 2016-06-14 17:40:55]

sdefresne@chromium.org changed reviewers:
+ brettw@chromium.org

[sdefresne, 2016-06-14 17:45:10]

Please take a look.

https://codereview.chromium.org/2063243002/diff/1/tools/gn/xcode_writer.cc
File tools/gn/xcode_writer.cc (right):

https://codereview.chromium.org/2063243002/diff/1/tools/gn/xcode_writer.cc#ne...
tools/gn/xcode_writer.cc:227: Settings* null_settings = nullptr;
I'm not sure about this code. Previously the code used
build_settings->build_args() which was incorrect, so now it uses the
declared_args default value or their overrides but I still have to code some of
the logic that sets target_cpu to host_cpu if target_cpu is not in build_args.

I'm also unsure about getting global variables "ios_deployment_target" and
"mac_deployment_target". It works with current Chromium build/config files but
do we really want to hard-code this? Should I instead leave all the key/value
pairs construction completely outside of gn binary and ask the user to pass them
on the command-line when passing --ide=xcode? If so, should I provide a script
that invokes "gn gen" with the values found in $output_dir/args.gn and
build/config/{ios,mac}/{ios,mac}_sdk.gni?

WDYT?

[brettw, 2016-06-14 17:55:15]

It seems like we might be adding this kind of thing forever. What about a
function in GN (maybe put the call in //build/toolchain/mac/BUILD.gn):
  set_ide_params("xcode") {
    ios_deployment_target = ...
    ...
  }
and then save that data somewhere for the IDE writer later on. By passing the
IDE type, we can use this same thing for other generators also. What do you
think?

[sdefresne, 2016-06-14 18:02:47]

On 2016/06/14 17:55:15, brettw wrote:
> It seems like we might be adding this kind of thing forever. What about a
> function in GN (maybe put the call in //build/toolchain/mac/BUILD.gn):
>   set_ide_params("xcode") {
>     ios_deployment_target = ...
>     ...
>   }
> and then save that data somewhere for the IDE writer later on. By passing the
> IDE type, we can use this same thing for other generators also. What do you
> think?

Sounds like an interesting idea.

I guess we should probably allow having multiple call to that function and
collect all the values (with warning about duplicates). I'll try to write a
quick design document and get it implemented. Thank you.

[brettw, 2016-06-14 21:06:56]

I would allow only one call per IDE type. The toolchain files should only loaded
in the default toolchain (and we can always put a conditional around them if
necessary). Hopefully everything that xcode needs can be plumbed in one place.