Create barbara_trims_a_stacktrace.md

[nikomatsakis]

Written with a bunch of fine people in an async vision doc writing session.

Closes #69

[eminence]

LGTM!

[eminence]

For an additional bit of color, maybe we can also mention Barbara's coworker who also complains about stack traces in LLDB:

• frame #0: 0x0000555555583d24 foo`foo::main::$u7b$$u7b$closure$u7d$$u7d$::$u7b$$u7b$closure$u7d$$u7d$::h617d49d0841ffc0d((null)=closure-0 @ 0x00007fffffffae38, (null)=) at main.rs:11:13

(click to see the full horrors)

* thread #1, name = 'foo', stop reason = breakpoint 1.1
  * frame #0: 0x0000555555583d24 foo`foo::main::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::h617d49d0841ffc0d((null)=closure-0 @ 0x00007fffffffae38, (null)=<unavailable>) at main.rs:11:13
    frame #1: 0x0000555555583d09 foo`_$LT$T$u20$as$u20$futures_util..fns..FnOnce1$LT$A$GT$$GT$::call_once::hc559b1f3f708a7b0(self=closure-0 @ 0x00007fffffffae68, arg=<unavailable>) at fns.rs:15:9
    frame #2: 0x000055555557f300 foo`_$LT$futures_util..future..future..map..Map$LT$Fut$C$F$GT$$u20$as$u20$core..future..future..Future$GT$::poll::hebf5b295fcc0837f(self=(pointer = 0x0000555555700e00), cx=0x00007fffffffcf50) at map.rs:57:73
    frame #3: 0x00005555555836ac foo`_$LT$futures_util..future..future..Map$LT$Fut$C$F$GT$$u20$as$u20$core..future..future..Future$GT$::poll::h482f253651b968e6(self=Pin<&mut futures_util::future::future::Map<tokio::time::driver::sleep::Sleep, closure-0>> @ 0x00007fffffffb268, cx=0x00007fffffffcf50)
at lib.rs:102:13
    frame #4: 0x000055555557995a foo`_$LT$futures_util..future..future..flatten..Flatten$LT$Fut$C$$LT$Fut$u20$as$u20$core..future..future..Future$GT$..Output$GT$$u20$as$u20$core..future..future..Future$GT$::poll::hd62d2a2417c0f2ea(self=(pointer = 0x0000555555700d80), cx=0x00007fffffffcf50) at flatten.rs:48:36
    frame #5: 0x00005555555834fc foo`_$LT$futures_util..future..future..Then$LT$Fut1$C$Fut2$C$F$GT$$u20$as$u20$core..future..future..Future$GT$::poll::hf60f05f9e9d6f307(self=Pin<&mut futures_util::future::future::Then<tokio::time::driver::sleep::Sleep, core::future::ready::Ready<()>, closure-0>> @ 0x00007fffffffc148, cx=0x00007fffffffcf50) at lib.rs:102:13
    frame #6: 0x000055555558474a foo`_$LT$core..pin..Pin$LT$P$GT$$u20$as$u20$core..future..future..Future$GT$::poll::h4dad267b4f10535d(self=Pin<&mut core::pin::Pin<alloc::boxed::Box<Future, alloc::alloc::Global>>> @ 0x00007fffffffc188, cx=0x00007fffffffcf50) at future.rs:119:9
    frame #7: 0x000055555557a693 foo`_$LT$futures_util..future..maybe_done..MaybeDone$LT$Fut$GT$$u20$as$u20$core..future..future..Future$GT$::poll::hdb6db40c2b3f2f1b(self=(pointer = 0x00005555557011b0), cx=0x00007fffffffcf50) at maybe_done.rs:95:38
    frame #8: 0x0000555555581254 foo`_$LT$futures_util..future..join_all..JoinAll$LT$F$GT$$u20$as$u20$core..future..future..Future$GT$::poll::ha2472a9a54f0e504(self=Pin<&mut futures_util::future::join_all::JoinAll<core::pin::Pin<alloc::boxed::Box<Future, alloc::alloc::Global>>>> @ 0x00007fffffffc388, cx=0x00007fffffffcf50) at join_all.rs:101:16
    frame #9: 0x0000555555584095 foo`foo::main::_$u7b$$u7b$closure$u7d$$u7d$::h6459086fc041943f((null)=ResumeTy @ 0x00007fffffffcc40) at main.rs:17:5
    frame #10: 0x0000555555580eab foo`_$LT$core..future..from_generator..GenFuture$LT$T$GT$$u20$as$u20$core..future..future..Future$GT$::poll::h272e2b5e808264a2(self=Pin<&mut core::future::from_generator::GenFuture<generator-0>> @ 0x00007fffffffccf8, cx=0x00007fffffffcf50) at mod.rs:80:19
    frame #11: 0x00005555555805a0 foo`tokio::park::thread::CachedParkThread::block_on::_$u7b$$u7b$closure$u7d$$u7d$::hbfc61d9f747eef7b at thread.rs:263:54
    frame #12: 0x00005555555795cc foo`tokio::coop::with_budget::_$u7b$$u7b$closure$u7d$$u7d$::ha229cfa0c1a2e13f(cell=0x00007ffff7c06712) at coop.rs:106:9
    frame #13: 0x00005555555773cc foo`std::thread::local::LocalKey$LT$T$GT$::try_with::h9a2f70c5c8e63288(self=0x00005555556e2a48, f=<unavailable>) at local.rs:272:16
    frame #14: 0x0000555555576ead foo`std::thread::local::LocalKey$LT$T$GT$::with::h12eeed0906b94d09(self=0x00005555556e2a48, f=<unavailable>) at local.rs:248:9
    frame #15: 0x000055555557fea6 foo`tokio::park::thread::CachedParkThread::block_on::h33b270af584419f1 [inlined] tokio::coop::with_budget::hcd477734d4970ed5(budget=(__0 = core::option::Option<u8> @ 0x00007fffffffd040), f=closure-0 @ 0x00007fffffffd048) at coop.rs:99:5
    frame #16: 0x000055555557fe73 foo`tokio::park::thread::CachedParkThread::block_on::h33b270af584419f1 [inlined] tokio::coop::budget::h410dced2a7df3ec8(f=closure-0 @ 0x00007fffffffd008) at coop.rs:76
    frame #17: 0x000055555557fe0c foo`tokio::park::thread::CachedParkThread::block_on::h33b270af584419f1(self=0x00007fffffffd078, f=<unavailable>) at thread.rs:263
    frame #18: 0x0000555555578f76 foo`tokio::runtime::enter::Enter::block_on::h4a9c2602e7b82840(self=0x00007fffffffd0f8, f=<unavailable>) at enter.rs:151:13
    frame #19: 0x000055555558482b foo`tokio::runtime::thread_pool::ThreadPool::block_on::h6b211ce19db8989d(self=0x00007fffffffd280, future=(__0 = foo::main::generator-0 @ 0x00007fffffffd200)) at mod.rs:71:9
    frame #20: 0x0000555555583324 foo`tokio::runtime::Runtime::block_on::h5f6badd2dffadf55(self=0x00007fffffffd278, future=(__0 = foo::main::generator-0 @ 0x00007fffffffd968)) at mod.rs:452:43
    frame #21: 0x0000555555579052 foo`foo::main::h3106d444f509ad81 at main.rs:5:1
    frame #22: 0x000055555557b69b foo`core::ops::function::FnOnce::call_once::hba86afc3f8197561((null)=(foo`foo::main::h3106d444f509ad81 at main.rs:6), (null)=<unavailable>) at function.rs:227:5
    frame #23: 0x0000555555580efe foo`std::sys_common::backtrace::__rust_begin_short_backtrace::h856d648367895391(f=(foo`foo::main::h3106d444f509ad81 at main.rs:6)) at backtrace.rs:125:18
    frame #24: 0x00005555555842f1 foo`std::rt::lang_start::_$u7b$$u7b$closure$u7d$$u7d$::h24c58cd1e112136f at rt.rs:66:18
    frame #25: 0x0000555555670aca foo`std::rt::lang_start_internal::h965c28c9ce06ee73 [inlined] core::ops::function::impls::_$LT$impl$u20$core..ops..function..FnOnce$LT$A$GT$$u20$for$u20$$RF$F$GT$::call_once::hbcc915e668c7ca11 at function.rs:259:13
    frame #26: 0x0000555555670ac3 foo`std::rt::lang_start_internal::h965c28c9ce06ee73 [inlined] std::panicking::try::do_call::h6b0f430d48122ddf at panicking.rs:379
    frame #27: 0x0000555555670ac3 foo`std::rt::lang_start_internal::h965c28c9ce06ee73 [inlined] std::panicking::try::h6ba420e2e21b5afa at panicking.rs:343
    frame #28: 0x0000555555670ac3 foo`std::rt::lang_start_internal::h965c28c9ce06ee73 [inlined] std::panic::catch_unwind::h8366719d1f615eee at panic.rs:431
    frame #29: 0x0000555555670ac3 foo`std::rt::lang_start_internal::h965c28c9ce06ee73 at rt.rs:51
    frame #30: 0x00005555555842d0 foo`std::rt::lang_start::ha8694bc6fe5182cd(main=(foo`foo::main::h3106d444f509ad81 at main.rs:6), argc=1, argv=0x00007fffffffdc88) at rt.rs:65:5
    frame #31: 0x00005555555790ec foo`main + 28
    frame #32: 0x00007ffff7c2f09b libc.so.6`__libc_start_main(main=(foo`main), argc=1, argv=0x00007fffffffdc88, init=<unavailable>, fini=<unavailable>, rtld_fini=<unavailable>, stack_end=0x00007fffffffdc78) at libc-start.c:308:16

[rylev]

Looks great!