Assert when using FORCE_MAC_TOOLCHAIN and target_os=ios.

iOS no longer uses the hermetic Xcode toolchain.

Bug: 939785
Change-Id: I31a28e77a7e2b5b43f3db43c39ada9d9e6757540
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539798
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Auto-Submit: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644418}

build/mac/should_use_hermetic_xcode.py

@@ -7,6 +7,7 @@
 Prints "1" if Chrome targets should be built with hermetic Xcode.
 Prints "2" if Chrome targets should be built with hermetic Xcode, but the OS
 version does not meet the minimum requirements of the hermetic version of Xcode.
+Prints "3" if FORCE_MAC_TOOLCHAIN is set for an iOS target_os
 Otherwise prints "0".
 
 Usage:
@@ -28,8 +29,11 @@ def _IsCorpMachine():
 
 
 def main():
+  force_toolchain = os.environ.get('FORCE_MAC_TOOLCHAIN')
+  if force_toolchain and sys.argv[1] == 'ios':
+    return "3"
   allow_corp = sys.argv[1] == 'mac' and _IsCorpMachine()
-  if os.environ.get('FORCE_MAC_TOOLCHAIN') or allow_corp:
+  if force_toolchain or allow_corp:
     if not mac_toolchain.PlatformMeetsHermeticXcodeRequirements():
       return "2"
     return "1"

build_overrides/build.gni

@@ -42,7 +42,7 @@ declare_args() {
   # This does not affect the compiler. When this variable is false, targets will
   # instead use a hermetic install of Xcode. [The hermetic install can be
   # obtained with gclient sync after setting the environment variable
-  # FORCE_MAC_TOOLCHAIN].
+  # FORCE_MAC_TOOLCHAIN for target_os mac only].
   use_system_xcode = ""
 }
 
@@ -54,5 +54,9 @@ if (host_os == "mac" && use_system_xcode == "") {
   assert(_result != 2,
          "Do not allow building targets with the default" +
              "hermetic toolchain if the minimum OS version is not met.")
+  assert(_result != 3,
+         "iOS does not support building with a hermetic toolchain. " +
+             "Please install Xcode.")
+
   use_system_xcode = _result != 1
 }