Need more verbose output with x.py build

[jessicah]

Running ./x.py build -vv only outputs the rustc compilation command, which is insufficient.

For example, it should direct rustc to provide more verbose output as well, e.g. the linking steps, and where object files are created from cpp source files, these compilation steps as well.

I've tried various incantations, such as RUSTC_FLAGS="-Z verbose -Z print-link-args --verbose" RUSTC_VERBOSE=10 ./x.py build -vv --stage 0 src/librustc but I'm not getting any further useful output.

[Mark-Simulacrum]

I think the expected approach today is to use RUSTFLAGS when more information from rustc is needed. It's not ideal (need to recompile everything) but otherwise should work.

@alexcrichton Is there some flag we can pass to rustc to have 'verbose' step output?

[jessicah]

I've also tried with RUSTC_FLAGS="-Z verbose -Z print-link-args --verbose", but then I run into a problem with cargo: https://github.com/rust-lang/cargo/blob/master/src/cargo/ops/cargo_rustc/mod.rs#L371 which seems to be a consequence of https://github.com/rust-lang/rust/blob/master/src/bootstrap/compile.rs#L802

I've tried removing that, but then I get an error:

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /checkout/src/libcore/option.rs:335:20

Full backtrace:

stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:380
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:396
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:611
   5: std::panicking::begin_panic_new
             at /checkout/src/libstd/panicking.rs:553
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:521
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:497
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:92
   9: core::panicking::panic
             at /checkout/src/libcore/panicking.rs:51
  10: <core::option::Option<T>>::unwrap
  11: bootstrap::compile::run_cargo
  12: <bootstrap::compile::Std as bootstrap::builder::Step>::run
  13: bootstrap::builder::Builder::ensure
  14: <bootstrap::compile::Test as bootstrap::builder::Step>::run
  15: bootstrap::builder::Builder::ensure
  16: <bootstrap::compile::Rustc as bootstrap::builder::Step>::run
  17: bootstrap::builder::Builder::ensure
  18: <bootstrap::compile::Rustc as bootstrap::builder::Step>::make_run
  19: bootstrap::builder::StepDescription::maybe_run
  20: bootstrap::builder::StepDescription::run
  21: bootstrap::builder::Builder::run
  22: bootstrap::Build::build
  23: bootstrap::main
  24: __rust_maybe_catch_panic
             at /checkout/src/libpanic_unwind/lib.rs:98
  25: std::rt::lang_start
             at /checkout/src/libstd/panicking.rs:458
             at /checkout/src/libstd/panic.rs:361
             at /checkout/src/libstd/rt.rs:59
  26: main
  27: __libc_start_main
  28: _start
Traceback (most recent call last):
  File "./x.py", line 20, in <module>
    bootstrap.main()
  File "/home/jessicah/rust/src/bootstrap/bootstrap.py", line 761, in main
    bootstrap()
  File "/home/jessicah/rust/src/bootstrap/bootstrap.py", line 752, in bootstrap
    run(args, env=env, verbose=build.verbose)
  File "/home/jessicah/rust/src/bootstrap/bootstrap.py", line 148, in run
    raise RuntimeError(err)

[petrochenkov]

I've also tried with RUSTC_FLAGS="-Z verbose -Z print-link-args --verbose", but then I run into a problem with cargo

#43855 strikes again

[o01eg]

Same for RUST_LOG=info:

INFO:rustc::traits::fulfill: selecting trait `Binder(TraitPredicate(<u64 as convert::From<isize>>))` at depth 0 yielded Err
INFO:rustc::traits::trans: Cache miss: Binder(<T as num::dec2flt::rawfp::RawFloat>) => VtableParam([])
INFO:rustc::traits::trans: Cache miss: Binder(<f32 as num::dec2flt::rawfp::RawFloat>) => VtableImpl(impl_def_id=DefId { krate: CrateNum(0), index: DefIndex(0:388) => core[9097]::num[0]::dec2flt[0]::rawfp[0]::{{impl}}[1] }, substs=Slice([]), nested=[])
INFO:rustc::traits::trans: Cache miss: Binder(<f64 as num::dec2flt::rawfp::RawFloat>) => VtableImpl(impl_def_id=DefId { krate: CrateNum(0), index: DefIndex(0:401) => core[9097]::num[0]::dec2flt[0]::rawfp[0]::{{impl}}[2] }, substs=Slice([]), nested=[])
INFO:cargo::ops::cargo_rustc::job_queue: end: core v0.0.0 (file:///tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/src/libcore) => Target(lib)/Profile(build) => Target
error: Could not compile `core`.

Caused by:
  failed to parse process output: `/tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/build/bootstrap/debug/rustc --crate-name core src/libcore/lib.rs --error-format json --crate-type lib --emit=dep-info,link -C opt-level=2 -C metadata=63e74be82340645b -C extra-filename=-63e74be82340645b --out-dir /tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/build/x86_64-unknown-linux-gnu/stage0-std/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/build/x86_64-unknown-linux-gnu/stage0-std/x86_64-unknown-linux-gnu/release/deps -L dependency=/tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/build/x86_64-unknown-linux-gnu/stage0-std/release/deps` (exit code: 0)

Caused by:
  compiler stdout is not empty: `Pre-trans`
thread 'main' panicked at 'command did not execute successfully: "/tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "7" "-v" "--release" "--locked" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/tmp/portage/dev-lang/rust-9999-r1/work/rust-git-src/src/libstd/Cargo.toml" "--message-format" "json"
expected success, got: exit code: 101', src/bootstrap/compile.rs:882:8

[pnkfelix]

See also #38686