[flutter_tools] port bash script to use sysctl not uname on macOS (#101308)

bin/internal/update_dart_sdk.sh

@@ -20,12 +20,13 @@ DART_SDK_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk"
 DART_SDK_PATH_OLD="$DART_SDK_PATH.old"
 ENGINE_STAMP="$FLUTTER_ROOT/bin/cache/engine-dart-sdk.stamp"
 ENGINE_VERSION=`cat "$FLUTTER_ROOT/bin/internal/engine.version"`
+OS="$(uname -s)"
 
 if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; then
   command -v curl > /dev/null 2>&1 || {
     >&2 echo
     >&2 echo 'Missing "curl" tool. Unable to download Dart SDK.'
-    case "$(uname -s)" in
+    case "$OS" in
       Darwin)
         >&2 echo 'Consider running "brew install curl".'
         ;;
@@ -42,7 +43,7 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
   command -v unzip > /dev/null 2>&1 || {
     >&2 echo
     >&2 echo 'Missing "unzip" tool. Unable to extract Dart SDK.'
-    case "$(uname -s)" in
+    case "$OS" in
       Darwin)
         echo 'Consider running "brew install unzip".'
         ;;
@@ -56,8 +57,30 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
     echo
     exit 1
   }
-  >&2 echo "Downloading Dart SDK from Flutter engine $ENGINE_VERSION..."
 
+  # `uname -m` may be running in Rosetta mode, instead query sysctl
+  if [ "$OS" = 'Darwin' ]; then
+    # Allow non-zero exit so we can do control flow
+    set +e
+    # -n means only print value, not key
+    QUERY="sysctl -n hw.optional.arm64"
+    # Do not wrap $QUERY in double quotes, otherwise the args will be treated as
+    # part of the command
+    QUERY_RESULT=$($QUERY 2>/dev/null)
+    if [ $? -eq 1 ]; then
+      # If this command fails, we're certainly not on ARM
+      ARCH='x64'
+    elif [ "$QUERY_RESULT" = '0' ]; then
+      # If this returns 0, we are also not on ARM
+      ARCH='x64'
+    elif [ "$QUERY_RESULT" = '1' ]; then
+      ARCH='arm64'
+    else
+      >&2 echo "'$QUERY' returned unexpected output: '$QUERY_RESULT'"
+      exit 1
+    fi
+    set -e
+  else
     # On x64 stdout is "uname -m: x86_64"
     # On arm64 stdout is "uname -m: aarch64, arm64_v8a"
     case "$(uname -m)" in
@@ -68,8 +91,9 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
         ARCH="arm64"
         ;;
     esac
+  fi
 
-  case "$(uname -s)" in
+  case "$OS" in
     Darwin)
       DART_ZIP_NAME="dart-sdk-darwin-${ARCH}.zip"
       IS_USER_EXECUTABLE="-perm +100"
@@ -88,6 +112,8 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
       ;;
   esac
 
+  >&2 echo "Downloading $OS $ARCH Dart SDK from Flutter engine $ENGINE_VERSION..."
+
   # Use the default find if possible.
   if [ -e /usr/bin/find ]; then
     FIND=/usr/bin/find