[ios] Fix `gn gen ...` for fat builds

When doing a fat builds, some template needs to have different expansion
(as some things are only done for the primary architecture like creating
the fat binary, ...). This mean that some variables are not used for the
second architectures, resulting in warning from gn about unused variables.

Fix this by using `not_needed` when appropriate (and convert the old
code that used `assert`). Also add some forwarding targets (like +bundle).

Bug: none
Change-Id: I46474826c8c28778fc9fa27e5992d193ec32f827
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2201758Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768813}

build/config/ios/rules.gni

@@ -7,8 +7,10 @@ import("//build/config/mac/base_rules.gni")
 import("//build/config/mac/symbols.gni")
 import("//build/toolchain/toolchain.gni")
 
-# Constants corresponding to the bundle type identifier for XCTest and XCUITest
-# targets.
+# Constants corresponding to the bundle type identifiers use application,
+# application extension, XCTest and XCUITest targets respectively.
+_ios_xcode_app_bundle_id = "com.apple.product-type.application"
+_ios_xcode_appex_bundle_id = "com.apple.product-type.app-extension"
 _ios_xcode_xctest_bundle_id = "com.apple.product-type.bundle.unit-test"
 _ios_xcode_xcuitest_bundle_id = "com.apple.product-type.bundle.ui-testing"
 
@@ -598,10 +600,7 @@ template("ios_app_bundle") {
   _default_variant = _variants[0]
 
   if (current_toolchain != default_toolchain) {
-    # For use of _variants and _default_variant for secondary toolchain to
-    # avoid the "Assignment had no effect" error from gn.
-    assert(_variants != [])
-    assert(_default_variant.target_name != "")
+    not_needed("*")
   }
 
   source_set(_arch_executable_source) {
@@ -792,8 +791,7 @@ template("ios_app_bundle") {
       }
     }
 
-    _app_product_type = "com.apple.product-type.application"
-    _product_type = _app_product_type
+    _product_type = _ios_xcode_app_bundle_id
     if (defined(invoker.product_type)) {
       _product_type = invoker.product_type
     }
@@ -806,7 +804,7 @@ template("ios_app_bundle") {
 
     # Only write PkgInfo for real application, not application extension (they
     # have the same product type but a different extension).
-    _write_pkg_info = _product_type == _app_product_type &&
+    _write_pkg_info = _product_type == _ios_xcode_app_bundle_id &&
                       _bundle_extension == _app_bundle_extension
 
     if (_write_pkg_info) {
@@ -951,7 +949,7 @@ template("ios_appex_bundle") {
                              "product_type",
                            ])
     bundle_extension = ".appex"
-    product_type = "com.apple.product-type.app-extension"
+    product_type = _ios_xcode_appex_bundle_id
 
     # Add linker flags required for an application extension (determined by
     # inspecting the link command-line when using Xcode 9.0+).
@@ -1376,9 +1374,12 @@ template("ios_framework_bundle") {
       all_dependent_configs += [ ":$_framework_public_config" ]
     }
 
-    if (defined(invoker.bundle_deps)) {
-      assert(invoker.bundle_deps != [], "mark bundle_deps as used")
+    group("$_target_name+bundle") {
+      forward_variables_from(invoker, [ "testonly" ])
+      public_deps = [ ":$_target_name+bundle($default_toolchain)" ]
     }
+
+    not_needed(invoker, "*")
   } else {
     if (_has_public_headers) {
       _public_headers = invoker.public_headers
@@ -1620,9 +1621,9 @@ template("ios_xctest_bundle") {
   # Silence "assignment had no effect" error for non-default toolchains as
   # following variables are only used in the expansion of the template for the
   # default toolchain.
-  assert(invoker.configs != [])
-  assert(invoker.host_target != target_name)
-  assert(invoker.xcode_test_application_name != target_name)
+  if (current_toolchain != default_toolchain) {
+    not_needed(invoker, "*")
+  }
 
   _target_name = target_name
   _output_name = target_name
@@ -1669,12 +1670,7 @@ template("ios_xctest_bundle") {
       public_deps = [ ":$_arch_loadable_module_target" ]
     }
 
-    # Force the use of invoker.xctest_bundle_principal_class if it is
-    # defined to prevent error about unused variable while generating
-    # the targets.
-    assert(!defined(invoker.xctest_bundle_principal_class) ||
-               invoker.xctest_bundle_principal_class != "",
-           "xctest_bundle_principal_class must not be empty if defined")
+    not_needed(invoker, "*")
   } else {
     _info_plist_target = _target_name + "_info_plist"
     _info_plist_bundle = _target_name + "_info_plist_bundle"
@@ -1981,7 +1977,7 @@ template("ios_xcuitest_test_runner_bundle") {
     bundle_binary_target = "//build/config/ios:xctest_runner_without_arm64e"
     bundle_binary_output = "XCTRunner"
     bundle_extension = ".app"
-    product_type = "com.apple.product-type.application"
+    product_type = _ios_xcode_app_bundle_id
 
     output_name = _output_name