From a3417bea6de74d15966cedd30c3e497558fc77f2 Mon Sep 17 00:00:00 2001
From: George Wright <gw280@google.com>
Date: Tue, 29 Dec 2020 18:21:05 -0800
Subject: [PATCH 1/4] Support ARM64 iOS simulator builds

---
 build/config/BUILDCONFIG.gn  |  6 +++++-
 build/toolchain/mac/BUILD.gn | 18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 44c276c80d..b43a3afb67 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -543,7 +543,11 @@ if (custom_toolchain != "") {
   import("//build/config/ios/ios_sdk.gni")  # For use_ios_simulator
   host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
   if (use_ios_simulator) {
-    set_default_toolchain("//build/toolchain/mac:ios_clang_x64")
+    if (target_cpu == "arm" || target_cpu == "arm64") {
+      set_default_toolchain("//build/toolchain/mac:ios_clang_arm_sim")
+    } else {
+      set_default_toolchain("//build/toolchain/mac:ios_clang_x64_sim")
+    }
   } else {
     set_default_toolchain("//build/toolchain/mac:ios_clang_arm")
   }
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 6b898234aa..b87e3ba0e7 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -250,8 +250,22 @@ mac_toolchain("ios_clang_arm") {
   sysroot_flags = "-isysroot $ios_device_sdk_path -miphoneos-version-min=$ios_deployment_target"
 }
 
-# Toolchain used for iOS simulator targets.
-mac_toolchain("ios_clang_x64") {
+# Toolchain used for iOS simulator targets (arm64).
+mac_toolchain("ios_clang_arm_sim") {
+  toolchain_cpu = "arm"
+  toolchain_os = "mac"
+  # TODO(gw280): We have to use llvm from xcode until we upgrade our copy of llvm
+  ar = "ar"
+  cc = "clang"
+  cxx = "clang++"
+  ld = "clang++"
+  is_clang = true
+  # We have to ignore unknown options and range loop analysis as this isn't our expected toolchain
+  sysroot_flags = "-isysroot $ios_simulator_sdk_path -mios-simulator-version-min=$ios_deployment_target -Wno-unknown-warning-option -Wno-range-loop-analysis"
+}
+
+# Toolchain used for iOS simulator targets (x64).
+mac_toolchain("ios_clang_x64_sim") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
   prefix = rebase_path(llvm_bin_path, root_build_dir)

From 8f51a47242ab2e5430f43f3f9f2147b02d313f21 Mon Sep 17 00:00:00 2001
From: George Wright <gw280@google.com>
Date: Fri, 22 Jan 2021 15:42:56 -0800
Subject: [PATCH 2/4] extra flags aren't necessary if `use_xcode` is set

---
 build/toolchain/mac/BUILD.gn | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index b87e3ba0e7..fe3a87fa4c 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -254,14 +254,19 @@ mac_toolchain("ios_clang_arm") {
 mac_toolchain("ios_clang_arm_sim") {
   toolchain_cpu = "arm"
   toolchain_os = "mac"
-  # TODO(gw280): We have to use llvm from xcode until we upgrade our copy of llvm
-  ar = "ar"
-  cc = "clang"
-  cxx = "clang++"
-  ld = "clang++"
+  if (!use_xcode) {
+    prefix = rebase_path(llvm_bin_path, root_build_dir)
+    ar = "$prefix/llvm-ar"
+    cc = "$prefix/clang"
+    cxx = "$prefix/clang++"
+  } else {
+    ar = "ar"
+    cc = "clang"
+    cxx = "clang++"
+  }
+  ld = cxx
   is_clang = true
-  # We have to ignore unknown options and range loop analysis as this isn't our expected toolchain
-  sysroot_flags = "-isysroot $ios_simulator_sdk_path -mios-simulator-version-min=$ios_deployment_target -Wno-unknown-warning-option -Wno-range-loop-analysis"
+  sysroot_flags = "-isysroot $ios_simulator_sdk_path -mios-simulator-version-min=$ios_deployment_target"
 }
 
 # Toolchain used for iOS simulator targets (x64).

From 356dce2285e6b20e71487a5e45de9c5e52527fa7 Mon Sep 17 00:00:00 2001
From: George Wright <gw280@google.com>
Date: Fri, 22 Jan 2021 15:47:42 -0800
Subject: [PATCH 3/4] Set `use_xcode` if building for ARM64 simulator

---
 build/toolchain/clang.gni | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/build/toolchain/clang.gni b/build/toolchain/clang.gni
index 021b141698..097b4ff384 100644
--- a/build/toolchain/clang.gni
+++ b/build/toolchain/clang.gni
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/ios/ios_sdk.gni") # For use_ios_simulator
+
 declare_args() {
   # Enable the optional type profiler in Clang, which will tag heap allocations
   # with the allocation type.
@@ -26,5 +28,7 @@ declare_args() {
   # TODO(dnfield): We shouldn't need Xcode for bitcode_marker builds, but we do
   # until libpng and dart have explicitly added LLVM asm sections to their
   # assembly sources. https://github.com/flutter/flutter/issues/39281
-  use_xcode = enable_bitcode
+  # TODO(gw280): Once our own copy of clang 12 is capable of building for arm64 simulator,
+  # we can safely remove the requirement that we use xcode for arm64 simulator builds.
+  use_xcode = enable_bitcode || (use_ios_simulator && (target_cpu == "arm" || target_cpu == "arm64"))
 }

From 68607df1e1d7db211b378610b80b93d1bbffe00b Mon Sep 17 00:00:00 2001
From: George Wright <gw280@google.com>
Date: Thu, 28 Jan 2021 15:13:07 -0800
Subject: [PATCH 4/4] Add issue link

---
 build/toolchain/mac/BUILD.gn | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index fe3a87fa4c..742adcb71f 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -260,6 +260,8 @@ mac_toolchain("ios_clang_arm_sim") {
     cc = "$prefix/clang"
     cxx = "$prefix/clang++"
   } else {
+    # TODO: https://github.com/harfbuzz/harfbuzz/issues/2834
+    # harfbuzz has a non-fatal warning right now with Xcode 12
     ar = "ar"
     cc = "clang"
     cxx = "clang++"