0.293440230s  INFO prepare_target{force=false package_id=sysroot v0.0.0 (/home/jyn/src/rust2/library/sysroot) target="sysroot"}: cargo::core::compiler::fingerprint: fingerprint error for sysroot v0.0.0 (/home/jyn/src/rust2/library/sysroot)/Build/TargetInner { name_inferred: true, ..: lib_target("sysroot", ["lib"], "/home/jyn/src/rust2/library/sysroot/src/lib.rs", Edition2021) }
...
```

In most cases this should not be necessary.

TODO: we should convert all this to structured logging so it's easier to control precisely.

## `tracing` in bootstrap

Bootstrap has conditional [`tracing`][tracing] setup to provide structured logging.


### Enabling `tracing` output

Bootstrap will conditionally build `tracing` support and enable `tracing` output if the `BOOTSTRAP_TRACING` env var is set.

#### Basic usage

Example basic usage[^just-trace]:


```bash
$ BOOTSTRAP_TRACING=bootstrap=TRACE ./x build library --stage 1
```

Example output[^unstable]:

```
$ BOOTSTRAP_TRACING=bootstrap=TRACE ./x check src/bootstrap/
Building bootstrap
   Compiling bootstrap v0.0.0 (/home/joe/repos/rust/src/bootstrap)
    Finished `dev` profile [unoptimized] target(s) in 2.74s
 DEBUG bootstrap parsing flags
 bootstrap::core::config::flags::Flags::parse args=["check", "src/bootstrap/"]
 DEBUG bootstrap parsing config based on flags
 DEBUG bootstrap creating new build based on config
 bootstrap::Build::build
  TRACE bootstrap setting up job management
  TRACE bootstrap downloading rustfmt early
   bootstrap::handling hardcoded subcommands (Format, Suggest, Perf)
    DEBUG bootstrap not a hardcoded subcommand; returning to normal handling, cmd=Check { all_targets: false }
  DEBUG bootstrap handling subcommand normally
   bootstrap::executing real run
     bootstrap::(1) executing dry-run sanity-check
     bootstrap::(2) executing actual run
Checking stage0 library artifacts (x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.04s
Checking stage0 compiler artifacts {rustc-main, rustc_abi, rustc_arena, rustc_ast, rustc_ast_ir, rustc_ast_lowering, rustc_ast_passes, rustc_ast_pretty, rustc_attr_data_structures, rustc_attr_parsing, rustc_baked_icu_data, rustc_borrowck, rustc_builtin_macros, rustc_codegen_llvm, rustc_codegen_ssa, rustc_const_eval, rustc_data_structures, rustc_driver, rustc_driver_impl, rustc_error_codes, rustc_error_messages, rustc_errors, rustc_expand, rustc_feature, rustc_fluent_macro, rustc_fs_util, rustc_graphviz, rustc_hir, rustc_hir_analysis, rustc_hir_pretty, rustc_hir_typeck, rustc_incremental, rustc_index, rustc_index_macros, rustc_infer, rustc_interface, rustc_lexer, rustc_lint, rustc_lint_defs, rustc_llvm, rustc_log, rustc_macros, rustc_metadata, rustc_middle, rustc_mir_build, rustc_mir_dataflow, rustc_mir_transform, rustc_monomorphize, rustc_next_trait_solver, rustc_parse, rustc_parse_format, rustc_passes, rustc_pattern_analysis, rustc_privacy, rustc_query_impl, rustc_query_system, rustc_resolve, rustc_sanitizers, rustc_serialize, rustc_session, rustc_smir, rustc_span, rustc_symbol_mangling, rustc_target, rustc_trait_selection, rustc_traits, rustc_transmute, rustc_ty_utils, rustc_type_ir, rustc_type_ir_macros, stable_mir} (x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.23s
Checking stage0 bootstrap artifacts (x86_64-unknown-linux-gnu)
    Checking bootstrap v0.0.0 (/home/joe/repos/rust/src/bootstrap)