Linux: add option to use system nspr.

base/base.gyp

Index: base/base.gyp
diff --git a/base/base.gyp b/base/base.gyp
index a584ae425b1308ef5c12acb56c85fae979354846..8c354e083b34293c6829d8285a54dc882d517b3a 100644
--- a/base/base.gyp
+++ b/base/base.gyp
@@ -206,6 +206,11 @@
             }],
           ],
         }],
+        ['use_system_nspr==1', {
+          'dependencies': [
+            'third_party/nspr/nspr.gyp:nspr',
+          ],
+        }],

[Ryan Sleevi, 2013/01/03 18:51:35]

Why is this dependency not expressed in base.gypi, since that is what handles
the inclusion of the NSPR sources?

I don't like the disconnect from having the dependency in one file, but the
sources directive that necessitates or obviates that dependency in another.

[Paweł Hajdan Jr., 2013/01/04 18:01:31]

This is a problem I've hit multiple times with gyp. Generally having
dependencies in .gypi files doesn't seem to work. Here is an example how gyp
freaks out if I do that:

$ build/gyp_chromium -Duse_system_nspr=1
Updating projects from gyp files...
Traceback (most recent call last):
  File "build/gyp_chromium", line 144, in <module>
    sys.exit(gyp.main(args))
  File
"/usr/local/google/home/phajdan/chromium/src/tools/gyp/pylib/gyp/__init__.py",
line 524, in main
    return gyp_main(args)
  File
"/usr/local/google/home/phajdan/chromium/src/tools/gyp/pylib/gyp/__init__.py",
line 509, in gyp_main
    generator.GenerateOutput(flat_list, targets, data, params)
  File
"/usr/local/google/home/phajdan/chromium/src/tools/gyp/pylib/gyp/generator/make.py",
line 2046, in GenerateOutput
    for target in gyp.common.AllTargets(target_list, target_dicts, build_file):
  File
"/usr/local/google/home/phajdan/chromium/src/tools/gyp/pylib/gyp/common.py",
line 302, in AllTargets
    deptargets = DeepDependencyTargets(target_dicts, bftargets)
  File
"/usr/local/google/home/phajdan/chromium/src/tools/gyp/pylib/gyp/common.py",
line 286, in DeepDependencyTargets
    spec = target_dicts[r]
KeyError: 'third_party/nspr/nspr.gyp:nspr'

Maybe I'm doing things wrong, so I'm happy to learn the correct way.

[Ryan Sleevi, 2013/01/07 00:04:10]

You cannot modify dependencies while evaluating a target_conditions block, which
is what of base.gypi is executing under, since the dependency evaluation has
already been computed.

My problem in general with this is that it's the GYP code-smell equivalent to
having an extern'd variable, since it splits up the dependency and
that-which-has-the-dependency.

Regrettably, however, it seems necessary here and consistent with the other
bits, so I suppose this will do.

       ],
       'sources': [
         'third_party/nspr/prcpucfg.h',
@@ -716,6 +721,11 @@
             'win/win_util_unittest.cc',
           ],
         }],
+        ['use_system_nspr==1', {
+          'dependencies': [
+            'third_party/nspr/nspr.gyp:nspr',
+          ],
+        }],
       ],  # conditions
       'target_conditions': [
         ['OS == "ios"', {