Developer tips and tricks

cargo run-rustup

This is the easiest way to build rustup from source and test it against your current rustup installation. Compared to cargo run which executes rustup-init, cargo run-rustup runs rustup directly.

For example, if you want to run rustup show, you may execute:

> cargo run-rustup -- show

RUSTUP_FORCE_ARG0

Sometimes, you may want to test how rustup behaves when it’s invoked with an executable name different from rustup-init and rustup, such as rustc or cargo when testing the proxy mode. In this case, RUSTUP_FORCE_ARG0 can be used to force rustup into thinking it’s being invoked with the given name. Similar to cargo run-rustup, it directly runs on your existing rustup installation.

For example, if you want to run rustc --version, you may execute:

> cargo run --config env.RUSTUP_FORCE_ARG0=\'rustc\' -- --version

This command passes the RUSTUP_FORCE_ARG0 environment variable to the rustup-init binary without influencing the cargo run command itself, which is very important since cargo could also be a rustup proxy.

In fact, cargo run-rustup is simply implemented as an alias of cargo run --config env.RUSTUP_FORCE_ARG0=\'rustup\'.

RUSTUP_BACKTRACK_LIMIT

If it’s necessary to alter the backtracking limit from the default of half a release cycle for some reason, you can set the RUSTUP_BACKTRACK_LIMIT environment variable. If this is unparsable as an i32 or if it’s absent then the default of 21 days (half a cycle) is used. If it parses and is less than 1, it is clamped to 1 at minimum.

This is not meant for use by users, but can be suggested in diagnosing an issue should one arise with the backtrack limits.

RUSTUP_MAX_RETRIES

When downloading a file, rustup will retry the download a number of times. The default is 3 times, but if this variable is set to a valid usize then it is the max retry count. A value of 0 means no retries, thus the default of 3 will mean a download is tried a total of four times before failing out.

RUSTUP_BACKTRACE

By default while running tests, we unset some environment variables that will break our testing (like RUSTUP_TOOLCHAIN, SHELL, ZDOTDIR, RUST_BACKTRACE). But if you want to debug locally, you may need backtrace. RUSTUP_BACKTRACE is used like RUST_BACKTRACE to enable backtraces of failed tests.

NOTE: This is a backtrace for the test, not for any subprocess invocation of rustup process running in the test

$ RUSTUP_BACKTRACE=1 cargo test --release --test cli-v1 -- remove_toolchain_then_add_again
    Finished release [optimized] target(s) in 0.38s
     Running target\release\deps\cli_v1-1f29f824792f6dc1.exe

running 1 test
test remove_toolchain_then_add_again ... FAILED

failures:

---- remove_toolchain_then_add_again stdout ----
thread 'remove_toolchain_then_add_again' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 1142, kind: Other, message: "An attempt was made to create more links on a file than the file system supports." }', src\libcore\result.rs:999:5
stack backtrace:
   0: backtrace::backtrace::trace_unsynchronized
             at C:\Users\appveyor\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.29\src\backtrace\mod.rs:66
   1: std::sys_common::backtrace::_print
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\sys_common\backtrace.rs:47
   2: std::sys_common::backtrace::print
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\sys_common\backtrace.rs:36
   3: std::panicking::default_hook::{{closure}}
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:198
   4: std::panicking::default_hook
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:209
   5: std::panicking::rust_panic_with_hook
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:475
   6: std::panicking::continue_panic_fmt
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:382
   7: std::panicking::rust_begin_panic
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:309
   8: core::panicking::panic_fmt
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libcore\panicking.rs:85
   9: core::result::unwrap_failed
  10: cli_v1::mock::clitools::test
  11: alloc::boxed::{{impl}}::call_once<(),FnOnce<()>>
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\liballoc\boxed.rs:746
  12: panic_unwind::__rust_maybe_catch_panic
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libpanic_unwind\lib.rs:82
  13: std::panicking::try
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\libstd\panicking.rs:273
  14: std::panic::catch_unwind
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\libstd\panic.rs:388
  15: test::run_test::run_test_inner::{{closure}}
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libtest\lib.rs:1466
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    remove_toolchain_then_add_again

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 26 filtered out

error: test failed, to rerun pass '--test cli-v1'