Allow chromium to be built with some system libs by introducing...

build/SConscript.main

 # Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 import shutil
 import sys
 
 
 p = ARGUMENTS.get('PROGRESS')
@@ skipping 11 matching lines @@
 load = ARGUMENTS.get('LOAD')
 if load:
     load = load.split(',')
 else:
     load = []
 
 
 root_env = Environment(
     tools = ['component_setup'],
 
+    # Requested list of system (shared) libraries, from the comma separated
+    # SYSTEM_LIBS command-line argument
+    req_system_libs = [],
+    # All supported system libraries, for the help message
+    all_system_libs = [],
+
     CHROME_SRC_DIR = '$MAIN_DIR/..',
     DESTINATION_ROOT = '$MAIN_DIR/Hammer',
     TARGET_ROOT = '$DESTINATION_ROOT',
 
     # Where ComponentTestProgram() will build test executables.
     TESTS_DIR = '$TARGET_ROOT',
 
     # Where ComponentProgram() will build program executables.
     STAGING_DIR = '$TARGET_ROOT',
 
@@ skipping 46 matching lines @@
 
     PERL                  = 'perl',
     PERL_INCLUDE_FLAG     = '-I ',
     PERL_INCLUDE_SUFFIX   = '',
     _PERL_INCLUDE_FLAGS   = ('${_concat(PERL_INCLUDE_FLAG, '
                              'PERL_INCLUDE_PATH, '
                              'PERL_INCLUDE_SUFFIX,'
                              '__env__, RDirs, TARGET, SOURCE)}'),
 )
 
+root_env['req_system_libs'] = ARGUMENTS.get('SYSTEM_LIBS').split(',')
+
+def WantSystemLib(env, lib):
+  """
+  Return true if lib has been requested as a system library in SYSTEM_LIBS.
+  """
+  if lib not in env['all_system_libs']:
+    env['all_system_libs'].append(lib)
+  return (lib in env['req_system_libs'])
+root_env.AddMethod(WantSystemLib, "WantSystemLib")
 
 def ChromeProgram(env, *args, **kw):
   return env.ComponentProgram(*args, **kw)
 root_env.AddMethod(ChromeProgram)
 
 def ChromeTestProgram(env, *args, **kw):
   return env.ComponentTestProgram(*args, **kw)
 root_env.AddMethod(ChromeTestProgram)
 
 def ChromeStaticLibrary(env, *args, **kw):
@@ skipping 93 matching lines @@
 if LoadComponent('sdch'):
   sconscripts.append('$SDCH_DIR/SConscript')
 
 if LoadComponent('skia'):
   sconscripts.append('$SKIA_DIR/SConscript')
 
 if LoadComponent('testing'):
   sconscripts.append('$TESTING_DIR/SConscript.gtest')
 
 if LoadComponent('third_party'):
+  if not root_env.WantSystemLib('bzip2'):
+    sconscripts.append('$BZIP2_DIR/bzip2.scons')
+    root_env.Append(BZIP2_LIB = ['bzip2'])
+  else:
+    root_env.Append(BZIP2_LIB = ['bz2'])
+  if not root_env.WantSystemLib('libpng'):
+    sconscripts.append('$LIBPNG_DIR/libpng.scons')
+  if not root_env.WantSystemLib('libjpeg'):
+    sconscripts.append('$LIBJPEG_DIR/SConscript')
+  if not root_env.WantSystemLib('libxml'):
+    sconscripts.append('$LIBXML_DIR/SConscript')
+    root_env.Append(XML_LIB = ['libxml'])
+  else:
+    root_env.Append(XML_LIB = ['xml2'])
+  if not root_env.WantSystemLib('libxslt'):
+    sconscripts.append('$LIBXSLT_DIR/SConscript')
+  if not root_env.WantSystemLib('lzma_sdk'):
+    sconscripts.append('$LZMA_SDK_DIR/SConscript')
+  if not root_env.WantSystemLib('zlib'):
+    sconscripts.append('$ZLIB_DIR/zlib.scons')
+    root_env.Append(ZLIB_LIB = ['zlib'])
+  else:
+    root_env.Append(ZLIB_LIB = ['z'])
   sconscripts.extend([
       '$BSDIFF_DIR/SConscript',
-      '$BZIP2_DIR/bzip2.scons',
       '$ICU38_DIR/icu38.scons',
-      '$LIBPNG_DIR/libpng.scons',
-      '$LZMA_SDK_DIR/SConscript',
       '$MODP_B64_DIR/modp_b64.scons',
-      '$ZLIB_DIR/zlib.scons',
-      '$LIBJPEG_DIR/SConscript',
-      '$LIBXML_DIR/SConscript',
-      '$LIBXSLT_DIR/SConscript',
       '$BSPATCH_DIR/SConscript',
   ])
 
 if LoadComponent('v8') and root_env.Dir('$CHROME_SRC_DIR/v8').exists():
   sconscripts.append('$OBJ_ROOT/build/SConscript.v8')
 
 if LoadComponent('webkit'):
   sconscripts.append('$WEBKIT_DIR/SConscript')
 
 
@@ skipping 278 matching lines @@
     linux_env.ParseConfig('pkg-config --cflags --libs gtk+-2.0')
     linux_env.ParseConfig('pkg-config --cflags --libs pangoft2')
   except OSError, e:
     print ('\n'
         'Failed to find a package dependency.  Please install all the\n'
         'packages listed at\n'
         'http://code.google.com/p/chromium/wiki/LinuxBuildInstructions'
         '#Software_Requirements')
 
     sys.exit(1)
-
+  if root_env.WantSystemLib('libxml'):
+    try:
+      linux_env.ParseConfig('pkg-config --cflags --libs libxml-2.0')
+    except OSError, e:
+      print ('\n'
+          'libxml requested in SYSTEM_LIBS but not found\n')
+      sys.exit(1)
+  if root_env.WantSystemLib('libxslt'):
+    try:
+      linux_env.ParseConfig('pkg-config --cflags --libs libxslt')
+    except OSError, e:
+      print ('\n'
+          'libxslt requested in SYSTEM_LIBS but not found\n')
+      sys.exit(1)
 
 # --------------------------------------------------------------------------
 # Mac specific
 
 mac_env = root_env.Clone()
 environment_list.append(mac_env)
 mac_env.Tool('target_platform_mac')
 mac_env.Tool('target_debug')
 mac_env.Replace(
     BUILD_TYPE = 'debug-mac',
@@ skipping 20 matching lines @@
         '$CHROME_DIR/SConscript',
         '$GEARS_DIR/SConscript',
         '$GOOGLE_UPDATE_DIR/SConscript',
         '$RLZ_DIR/SConscript',
         '$SANDBOX_DIR/sandbox.scons',
         'build/SConscript.v8',
         '$WEBKIT_DIR/SConscript',
     ],
 )
 
-mac_env.Append(
+if not root_env.WantSystemLib('libevent'):
+  mac_env.Append(
     BUILD_SCONSCRIPTS = [
         '$LIBEVENT_DIR/libevent.scons',
     ],
+  )
+mac_env.Append(
     CFLAGS = [
         '-std=c99',
     ],
     CXXFLAGS = [
         '-fvisibility-inlines-hidden',
         '${str(SOURCE).endswith(".mm") and "-fobjc-gc" or ""}',
     ],
     CCFLAGS = [
         '-fmessage-length=0',
         '-pipe',
@@ skipping 56 matching lines @@
   )
 
 
 help_fmt = """
 Usage: hammer [SCONS_OPTIONS] [VARIABLES] [TARGET] ...
 
 Supported build variables:
   LOAD=[module,...]         Comma-separated list of components to load in the
                               dependency graph ('-' prefix excludes):
 %s
+  SYSTEM_LIBS=[lib,...]     Comma-separated list of system libraries to link
+                              dynamically (by default they are built in from
+                              included sources):
+%s
   PROGRESS=type             Display a progress indicator:
                               name:  print each evaluated target name
                               spinner:  print a spinner every 5 targets
   VERBOSE=1                 Display full command lines
 """
 
 if GetOption('help'):
   import textwrap
   tw = textwrap.TextWrapper(
     width = 78,
     initial_indent = ' '*32,
     subsequent_indent = ' '*32,
   )
   components = tw.fill(', '.join(components))
+  all_system_libs = tw.fill(', '.join(env['all_system_libs']))
 
-  Help(help_fmt % components)
+  Help(help_fmt % (components, all_system_libs))
 
 
 Import('build_component')
 Default(None)  # Reset default target to empty.
 Default(Alias(build_component))  # Set default target based on where built.
 
 # -------------------------------------------------------------------------
 
 # Invoke all the SConscripts in each of the environments that make sense on
 # this host-platform.
@@ skipping 49 matching lines @@
         'all_libraries',
         'all_languages',
         'all_programs',
         'all_test_programs',
     ], projects = [p],
     COMPONENT_VS_PROJECT_SCRIPT_PATH=(
         'cd $$(ProjectDir)/$VS_PROJECT_TO_MAIN_DIR && hammer.bat'),
 )
 
 # -------------------------------------------------------------------------