[xcode] Fix build script to build the correct target

Recent refactoring of GetBuildScript() forgot to pass the build
target to the ninja causing it to always build everything. This
causes builds to take longer than needed and to use more space
than available on some machines.

Bug: none
Change-Id: I92dfd9cc3b57e66d5b40acbc5a3e8b5c93319816
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/13040
Reviewed-by: Petr Hosek <phosek@google.com>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>

src/gn/xcode_writer.cc

diff --git a/src/gn/xcode_writer.cc b/src/gn/xcode_writer.cc
index 6dda1ac..809d6a7 100644
--- a/src/gn/xcode_writer.cc
+++ b/src/gn/xcode_writer.cc
@@ -97,15 +97,18 @@
   return buffer.str();
 }
 
-std::string GetBuildScript(const std::string& ninja_executable,
+std::string GetBuildScript(const std::string& target_name,
+                           const std::string& ninja_executable,
                            base::Environment* environment) {
   // Launch ninja with a sanitized environment (Xcode sets many environment
   // variables overridding settings, including the SDK, thus breaking hermetic
   // build).
   std::stringstream buffer;
   buffer << "exec env -i " << ComputeScriptEnviron(environment);
-  buffer << GetNinjaExecutable(ninja_executable) << " -C .\n";
-  buffer << "exit 1\n";
+  buffer << GetNinjaExecutable(ninja_executable) << " -C .";
+  if (!target_name.empty()) {
+    buffer << " '" << target_name << "'";
+  }
   return buffer.str();
 }
 
@@ -659,7 +662,8 @@
   std::unique_ptr<base::Environment> env(base::Environment::Create());
 
   project_.AddAggregateTarget(
-      "All", GetBuildScript(options_.ninja_executable, env.get()));
+      "All", GetBuildScript(options_.root_target_name,
+                            options_.ninja_executable, env.get()));
 
   const std::optional<std::vector<const Target*>> targets =
       GetTargetsFromBuilder(builder, err);
@@ -895,7 +899,7 @@
       target->output_name().empty() ? target->label().name()
                                     : target->output_name(),
       "com.apple.product-type.tool", output_dir,
-      GetBuildScript(options_.ninja_executable, env));
+      GetBuildScript(target->label().name(), options_.ninja_executable, env));
 }
 
 PBXNativeTarget* XcodeProject::AddBundleTarget(const Target* target,
@@ -925,7 +929,8 @@
   return project_.AddNativeTarget(
       pbxtarget_name, std::string(), target_output_name,
       target->bundle_data().product_type(), output_dir,
-      GetBuildScript(options_.ninja_executable, env), xcode_extra_attributes);
+      GetBuildScript(pbxtarget_name, options_.ninja_executable, env),
+      xcode_extra_attributes);
 }
 
 void XcodeProject::WriteFileContent(std::ostream& out) const {