Eliminate ASL-based stdout forwarding on iOS

lib/ui/dart_runtime_hooks.cc

@@ -25,6 +25,11 @@
 
 #if defined(OS_ANDROID)
 #include <android/log.h>
+#elif defined(OS_IOS)
+extern "C" {
+  // Cannot import the syslog.h header directly because of macro collision.
+  extern void syslog(int, const char*, ...);
+}
 #endif
 
 using tonic::LogIfError;
@@ -143,11 +148,15 @@ void Logger_PrintString(Dart_NativeArguments args) {
     // Write to the logcat on Android.
     const char* tag = Settings::Get().log_tag.c_str();
     __android_log_print(ANDROID_LOG_INFO, tag, "%.*s", (int)length, chars);
+#elif defined(OS_IOS)
+    // Write to syslog on iOS.
+    //
+    // TODO(cbracken): replace with dedicated communication channel and bypass
+    // iOS logging APIs altogether.
+    syslog(1 /* LOG_ALERT */, "%.*s", (int)length, chars);
 #else
-    // On Fuchsia, iOS and in flutter_tester (on both macOS and Linux), write
-    // directly to stdout. On iOS, this is redirected to ASL via
-    // RedirectIOConnectionsToSyslog in platform_mac.mm.
-    // TODO(cbracken): replace with dedicated (non-stdout) logging on iOS.
+    // On Fuchsia and in flutter_tester (on both macOS and Linux), write
+    // directly to stdout.
     fwrite(chars, 1, length, stdout);
     fputs("\n", stdout);
     fflush(stdout);

shell/common/switches.h

@@ -74,11 +74,6 @@ DEF_SWITCH(NonInteractive,
            "non-interactive",
            "Make the shell non-interactive. By default, the shell attempts "
            "to setup a window and create an OpenGL context.")
-DEF_SWITCH(NoRedirectToSyslog,
-           "no-redirect-to-syslog",
-           "On iOS: Don't redirect stdout and stderr to syslog by default. "
-           "This is used by the tools to read device logs. However, this can "
-           "cause logs to not show up when launched from Xcode.")
 DEF_SWITCH(Packages, "packages", "Specify the path to the packages.")
 DEF_SWITCH(StartPaused,
            "start-paused",

shell/platform/darwin/common/platform_mac.mm

@@ -6,8 +6,6 @@
 
 #include <Foundation/Foundation.h>
 
-#include <asl.h>
-
 #include "dart/runtime/include/dart_tools_api.h"
 #include "flutter/common/threads.h"
 #include "flutter/fml/trace_event.h"
@@ -20,17 +18,6 @@
 
 namespace shell {
 
-static void RedirectIOConnectionsToSyslog(const ftl::CommandLine& command_line) {
-#if TARGET_OS_IPHONE
-  if (command_line.HasOption(FlagForSwitch(Switch::NoRedirectToSyslog))) {
-    return;
-  }
-
-  asl_log_descriptor(NULL, NULL, ASL_LEVEL_NOTICE, STDOUT_FILENO, ASL_LOG_DESCRIPTOR_WRITE);
-  asl_log_descriptor(NULL, NULL, ASL_LEVEL_WARNING, STDERR_FILENO, ASL_LOG_DESCRIPTOR_WRITE);
-#endif
-}
-
 static ftl::CommandLine InitializedCommandLine() {
   std::vector<std::string> args_vector;
 
@@ -54,8 +41,6 @@ static void RedirectIOConnectionsToSyslog(const ftl::CommandLine& command_line)
 
     auto command_line = InitializedCommandLine();
 
-    RedirectIOConnectionsToSyslog(command_line);
-
     // This is about as early as tracing of any kind can start. Add an instant
     // marker that can be used as a reference for startup.
     TRACE_EVENT_INSTANT0("flutter", "main");