Only generate backtraces with RUST_BACKTRACE set (closes #7)

[birkenfeld]

No description provided.

[cramertj]

Typo: "and propagates"

[birkenfeld]

Thanks!

[brson]

@birkenfeld #[inline(always)] should fix the extra stack frame if you still want to do that.

[birkenfeld]

I thought so as well, but in debug mode it does not:

   0:     0x55615e0787c0 - backtrace::backtrace::libunwind::trace
                        at /home/gbr/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.2.3/src/backtrace/libunwind.rs:54
                         - backtrace::backtrace::trace<closure>
                        at /home/gbr/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.2.3/src/backtrace/mod.rs:70
   1:     0x55615e07913a - backtrace::capture::{{impl}}::new
                        at /home/gbr/devel/ext/error-chain/target/debug/build/backtrace-3bc1ff360ebb00cb/out/capture.rs:79
   2:     0x55615e070642 - {{inlined-root}}::make_backtrace
                        at /home/gbr/devel/ext/error-chain/src/lib.rs:685
                         - tests::has_backtrace_depending_on_env::{{impl}}::from
                        at /home/gbr/devel/ext/error-chain/<error_chain macros>:42
   3:     0x55615e0702e8 - tests::has_backtrace_depending_on_env
                        at /home/gbr/devel/ext/error-chain/tests/tests.rs:155
   4:     0x55615e08c6c6 - _<F as alloc..boxed..FnBox<A>>::call_box::h6c46b1f51a5f97cd
   5:     0x55615e0819eb - std::panicking::try::call::h8d6a00e6c0ac8b9e
   6:     0x55615e0cb0c6 - __rust_maybe_catch_panic
   7:     0x55615e08bf6c - _<F as alloc..boxed..FnBox<A>>::call_box::h173484225f9723d2
   8:     0x55615e0c12f7 - std::sys::thread::Thread::new::thread_start::h8f3bd45211e9f5ea
   9:     0x7fc160624423 - <unknown>
  10:     0x7fc160154ecc - clone
  11:                0x0 - <unknown>

Note the {{inlined-root}}::make_backtrace in there. Without inline(always):

   0:     0x55a6b9ade3a0 - backtrace::backtrace::libunwind::trace
                        at /home/gbr/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.2.3/src/backtrace/libunwind.rs:54
                         - backtrace::backtrace::trace<closure>
                        at /home/gbr/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.2.3/src/backtrace/mod.rs:70
   1:     0x55a6b9aded1a - backtrace::capture::{{impl}}::new
                        at /home/gbr/devel/ext/error-chain/target/debug/build/backtrace-3bc1ff360ebb00cb/out/capture.rs:79
   2:     0x55a6b9ad8c12 - error_chain::make_backtrace
                        at /home/gbr/devel/ext/error-chain/src/lib.rs:685
   3:     0x55a6b9ad52bf - tests::has_backtrace_depending_on_env::{{impl}}::from
                        at /home/gbr/devel/ext/error-chain/<error_chain macros>:42
   4:     0x55a6b9ad5038 - tests::has_backtrace_depending_on_env
                        at /home/gbr/devel/ext/error-chain/tests/tests.rs:155
   5:     0x55a6b9af22a6 - _<F as alloc..boxed..FnBox<A>>::call_box::h6c46b1f51a5f97cd
   6:     0x55a6b9ae75cb - std::panicking::try::call::h8d6a00e6c0ac8b9e
   7:     0x55a6b9b30ca6 - __rust_maybe_catch_panic
   8:     0x55a6b9af1b4c - _<F as alloc..boxed..FnBox<A>>::call_box::h173484225f9723d2
   9:     0x55a6b9b26ed7 - std::sys::thread::Thread::new::thread_start::h8f3bd45211e9f5ea
  10:     0x7f8a425b6423 - <unknown>
  11:     0x7f8a420e6ecc - clone
  12:                0x0 - <unknown>

In light of that, I think it's better to read with the explicit frame in there.

[brson]

Thanks!