Add support for multi-architecture application bundle on iOS.

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 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.
 
+if (target_os == "ios") {
+  declare_args() {
+    # If defined, then the build is a multi-architecture build (aka fat build)
+    # and target_cpu must not be defined. Any value supported by target_cpu can
+    # be used in this list.
+    multi_arch_target_cpus = []

[brettw, 2016/07/11 23:57:17]

[read the next comment first]

I'm trying *really* hard to keep stuff out of this file. This case I'm more
sympathetic to than many because this does seem like global build configuration,
but the only reason it's needed here (if you take my advice below to move the
toolchain list) is for the target_cpu variable.

At first I was thinking of making this variable in rules.gni, and then asserting
that multi_arch_target_cpus[0] == target_cpu. But that's annoying.

What do you think about making "additional_target_cpus" and then using
target_cpu + these to define the multi_arch_toolchains. This means you don't
have the annoying logic for making sure only one is used, target_cpu is always
well-defined to be the default main thing you set, and we can remove this code
from this file :)

[sdefresne, 2016/07/12 09:13:33]

Done.

+  }
+}
+
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
 #
 # Users typically only set the variables "target_os" and "target_cpu" in "gn
 # args", the rest are set up by our build and internal to GN.
 #
@@ skipping 23 matching lines @@
   target_os = host_os
 }
 
 if (target_cpu == "") {
   if (target_os == "android") {
     # If we're building for Android, we should assume that we want to
     # build for ARM by default, not the host_cpu (which is likely x64).
     # This allows us to not have to specify both target_os and target_cpu
     # on the command line.
     target_cpu = "arm"
+  } else if (target_os == "ios") {
+    # If we're building for iOS, we respect the multi_arch_target_cpus if
+    # it is defined. In that case, we pick the first architecture listed in
+    # multi_arch_target_cpus and use it as target_cpu, the others will be
+    # build as secondary toolchain by the ios_app_bundle target.
+    if (multi_arch_target_cpus != []) {
+      assert(target_cpu == "",
+             "cannot define both multi_arch_target_cpus and target_cpu")
+      target_cpu = multi_arch_target_cpus[0]
+    } else {
+      target_cpu = host_cpu
+    }
   } else {
     target_cpu = host_cpu
   }
 }
 
 if (current_cpu == "") {
   current_cpu = target_cpu
 }
 if (current_os == "") {
   current_os = target_os
@@ skipping 149 matching lines @@
   # See comments in build/toolchain/cros/BUILD.gn about board compiles.
   assert(host_os == "linux",
          "ChromeOS builds are only supported on Linux hosts.")
   if (is_clang) {
     _default_toolchain = "//build/toolchain/cros:clang_target"
   } else {
     _default_toolchain = "//build/toolchain/cros:target"
   }
 } else if (target_os == "ios") {
   _default_toolchain = "//build/toolchain/mac:ios_clang_$target_cpu"
+  assert(custom_toolchain == "" || multi_arch_target_cpus == [],
+         "cannot define both multi_arch_target_cpus and custom_toolchain")
+
+  # Initialize multi_arch_toolchains from multi_arch_target_cpus. The
+  # list will not contain the default_toolchain and may be empty while
+  # multi_arch_target_cpus is not. This allows the build to default to
+  # regular build if multi_arch_target_cpus contains a single cpu.
+  multi_arch_toolchains = []

[brettw, 2016/07/11 23:57:17]

Can this code by put into build/config/ios/rules.gni or perhaps a new .gni file
for this purpose?> I want to keep all non-essential logic out of BUILDCONFIG.

[sdefresne, 2016/07/12 09:13:33]

This will duplicate the "//build/toolchain/mac:ios_clang_$_cpu" string, but
probably minor regarding modifying this file. Done.

+  foreach(_multi_arch_target_cpu, multi_arch_target_cpus) {
+    if (_multi_arch_target_cpu != target_cpu) {
+      multi_arch_toolchains +=
+          [ "//build/toolchain/mac:ios_clang_$_multi_arch_target_cpu" ]
+    }
+  }
 } else if (target_os == "linux") {
   if (is_clang) {
     _default_toolchain = "//build/toolchain/linux:clang_$target_cpu"
   } else {
     _default_toolchain = "//build/toolchain/linux:$target_cpu"
   }
 } else if (target_os == "mac") {
   assert(host_os == "mac", "Mac cross-compiles are unsupported.")
   _default_toolchain = host_toolchain
 } else if (target_os == "win") {
@@ skipping 431 matching lines @@
     forward_variables_from(invoker, "*", [ "visibility" ])
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     if (!defined(deps)) {
       deps = []
     }
     deps += [ "//build/config/sanitizers:deps" ]
   }
 }