Auto merge of #38165 - Yamakaky:better-backtrace, r=petrochenkov

Improve backtrace formating while panicking.

Fixes #37783.

Done:

- Fix alignment of file paths for better readability
- `RUST_BACKTRACE=full` prints all the informations (current behaviour)
- `RUST_BACKTRACE=(short|yes)` is the default and does:
  - Skip irrelevant frames at the beginning and the end
  - Remove function address
  - Remove the current directory from the absolute paths
  - Remove `::hfabe6541873` at the end of the symbols
- `RUST_BACKTRACE=(0|no)` disables the backtrace.
- `RUST_BACKTRACE=<everything else>` is equivalent to `short` for
  backward compatibility.
- doc
- More uniform printing across platforms.

Removed, TODO in a new PR:

- Remove path prefix for libraries and libstd

Example of short backtrace:
```rust
fn fail() {
    panic!();
}

fn main() {
    let closure = || fail();
    closure();
}
```
Short:
```
thread 'main' panicked at 'explicit panic', t.rs:2
Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: t::fail
            at ./t.rs:2
   1: t::main::{{closure}}
            at ./t.rs:6
   2: t::main
            at ./t.rs:7
```
Full:
```
thread 'main' panicked at 'This function never returns!', t.rs:2
stack backtrace:
   0:     0x558ddf666478 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hec84c9dd8389cc5d
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x558ddf65d90e - std::sys_common::backtrace::_print::hfa25f8b31f4b4353
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:71
   2:     0x558ddf65cb5e - std::sys_common::backtrace::print::h9b711e11ac3ba805
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:60
   3:     0x558ddf66796e - std::panicking::default_hook::{{closure}}::h736d216e74748044
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:355
   4:     0x558ddf66743c - std::panicking::default_hook::h16baff397e46ea10
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:371
   5:     0x558ddf6682bc - std::panicking::rust_panic_with_hook::h6d5a9bb4eca42c80
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:559
   6:     0x558ddf64ea93 - std::panicking::begin_panic::h17dc549df2f10b99
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:521
   7:     0x558ddf64ec42 - t::diverges::he6bc43fc925905f5
                               at /tmp/p/t.rs:2
   8:     0x558ddf64ec5a - t::main::h0ffc20356b8a69c0
                               at /tmp/p/t.rs:6
   9:     0x558ddf6687f5 - core::ops::FnOnce::call_once::hce41f19c0db56f93
  10:     0x558ddf667cde - std::panicking::try::do_call::hd4c8c97efb4291df
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:464
  11:     0x558ddf698d77 - __rust_try
  12:     0x558ddf698c57 - __rust_maybe_catch_panic
                               at /home/yamakaky/dev/rust/rust/src/libpanic_unwind/lib.rs:98
  13:     0x558ddf667adb - std::panicking::try::h2c56ed2a59ec1d12
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:440
  14:     0x558ddf66cc9a - std::panic::catch_unwind::h390834e0251cc9af
                               at /home/yamakaky/dev/rust/rust/src/libstd/panic.rs:361
  15:     0x558ddf6809ee - std::rt::lang_start::hb73087428e233982
                               at /home/yamakaky/dev/rust/rust/src/libstd/rt.rs:57
  16:     0x558ddf64ec92 - main
  17:     0x7fecb869e290 - __libc_start_main
  18:     0x558ddf64e8b9 - _start
  19:                0x0 - <unknown>
```

2 files changed, 4 insertions, 3 deletions

diff --git a/src/test/run-pass/backtrace-debuginfo.rs b/src/test/run-pass/backtrace-debuginfo.rs
index 626eccfc9ec..88fee9ed25b 100644
--- a/src/test/run-pass/backtrace-debuginfo.rs
+++ b/src/test/run-pass/backtrace-debuginfo.rs
@@ -141,12 +141,12 @@ fn run_test(me: &str) {
     use std::process::Command;
 
     let mut template = Command::new(me);
-    template.env("RUST_BACKTRACE", "1");
+    template.env("RUST_BACKTRACE", "full");
 
     let mut i = 0;
     loop {
         let out = Command::new(me)
-                          .env("RUST_BACKTRACE", "1")
+                          .env("RUST_BACKTRACE", "full")
                           .arg(i.to_string()).output().unwrap();
         let output = str::from_utf8(&out.stdout).unwrap();
         let error = str::from_utf8(&out.stderr).unwrap();
diff --git a/src/test/run-pass/backtrace.rs b/src/test/run-pass/backtrace.rs
index 834ce984e66..b3a9e8928be 100644
--- a/src/test/run-pass/backtrace.rs
+++ b/src/test/run-pass/backtrace.rs
@@ -47,7 +47,7 @@ fn template(me: &str) -> Command {
 }
 
 fn expected(fn_name: &str) -> String {
-    format!(" - backtrace::{}", fn_name)
+    format!(" backtrace::{}", fn_name)
 }
 
 fn runtest(me: &str) {
@@ -58,6 +58,7 @@ fn runtest(me: &str) {
     let s = str::from_utf8(&out.stderr).unwrap();
     assert!(s.contains("stack backtrace") && s.contains(&expected("foo")),
             "bad output: {}", s);
+    assert!(s.contains(" 0:"), "the frame number should start at 0");
 
     // Make sure the stack trace is *not* printed
     // (Remove RUST_BACKTRACE from our own environment, in case developer