OS_ACTIVITY_MODE didn't work for me (it may have been because I typo'd disable as disabled, but isn't that more natural?!?), or at least didn't prevent a great deal of messages. So here's the real deal with the environment variables.
https://llvm.org/svn/llvm-project/lldb/trunk/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp
lldb_private::Error
PlatformDarwin::LaunchProcess(lldb_private::ProcessLaunchInfo &launch_info) {
// Starting in Fall 2016 OSes, NSLog messages only get mirrored to stderr
// if the OS_ACTIVITY_DT_MODE environment variable is set. (It doesn't
// require any specific value; rather, it just needs to exist).
// We will set it here as long as the IDE_DISABLED_OS_ACTIVITY_DT_MODE flag
// is not set. Xcode makes use of IDE_DISABLED_OS_ACTIVITY_DT_MODE to tell
// LLDB *not* to muck with the OS_ACTIVITY_DT_MODE flag when they
// specifically want it unset.
const char *disable_env_var = "IDE_DISABLED_OS_ACTIVITY_DT_MODE";
auto &env_vars = launch_info.GetEnvironmentEntries();
if (!env_vars.ContainsEnvironmentVariable(disable_env_var)) {
// We want to make sure that OS_ACTIVITY_DT_MODE is set so that
// we get os_log and NSLog messages mirrored to the target process
// stderr.
if (!env_vars.ContainsEnvironmentVariable("OS_ACTIVITY_DT_MODE"))
env_vars.AppendArgument(llvm::StringRef("OS_ACTIVITY_DT_MODE=enable"));
}
// Let our parent class do the real launching.
return PlatformPOSIX::LaunchProcess(launch_info);
}
So setting OS_ACTIVITY_DT_MODE to "NO" in the environment variables (GUI method explained in Schemes screenshot in main answer) makes it work for me.
As far as NSLog being the dumping ground for system messages, errors, and your own debugging: a real logging approach is probably called for anyway, e.g. https://github.com/fpillet/NSLogger .
OR
Drink the new Kool-Aid: http://asciiwwdc.com/2016/sessions/721 https://developer.apple.com/videos/play/wwdc2016/721/
It's not surprising that there are some hitches after overhauling the entire logging API.
ADDENDUM
Anyway, NSLog is just a shim:
https://developer.apple.com/library/content/releasenotes/Miscellaneous/RN-Foundation-OSX10.12/
NSLog / CFLog
NSLog is now just a shim to os_log in most circumstances.
Only makes sense now to quote the source for the other env variable. Quite a disparate place, this time from Apple internals. Not sure why they are overlapping. [Incorrect comment about NSLog removed]
[Edited 22 Sep]: I wonder what "release" and "stream" do differently than "debug". Not enough source.
https://github.com/macosforge/libdispatch/blob/8e63547ea4e5abbfe55c0c3064181c4950a791d3/src/voucher.c
e = getenv("OS_ACTIVITY_MODE");
if (e) {
if (strcmp(e, "release") == 0) {
mode = voucher_activity_mode_release;
} else if (strcmp(e, "debug") == 0) {
mode = voucher_activity_mode_debug;
} else if (strcmp(e, "stream") == 0) {
mode = voucher_activity_mode_stream;
} else if (strcmp(e, "disable") == 0) {
mode = voucher_activity_mode_disable;
}
}
