cargo-minimize

Install with cargo install --git https://github.com/Nilstrieb/cargo-minimize cargo-minimize and use with cargo minimize.

For more info, see the cookbook.

Idea

When encountering problems like internal compiler errors, it's often desirable to have a minimal reproduction that can be used by the people fixing the issue. Usually, these problems are found in big codebases. Getting from a big codebase to a small (<50 LOC) reproduction is non-trivial and requires a lot of manual work. cargo-minimize assists you with doing some minimization steps that can be easily automated for you.

How to use

For minimizing an internal compiler error on a normal cargo project, cargo minimize works out of the box. There are many configuration options available though.

Usage: cargo minimize [OPTIONS] [PATH]

Arguments:
  [PATH]  The directory/file of the code to be minimized [default: src]

Options:
      --extra-args <EXTRA_ARGS>
          Additional arguments to pass to cargo/rustc, separated by whitespace
      --cargo-subcmd <CARGO_SUBCMD>
          The cargo subcommand used to find the reproduction, seperated by whitespace (for example `miri run`) [default: build]
      --cargo-subcmd-lints <CARGO_SUBCMD_LINTS>
          The cargo subcommand used to get diagnostics like the dead_code lint from the compiler, seperated by whitespace. Defaults to the value of `--cargo-subcmd`
      --no-color
          To disable colored output
      --rustc
          This option bypasses cargo and uses rustc directly. Only works when a single file is passed as an argument
      --no-verify
          Skips testing whether the regression reproduces and just does the most aggressive minimization. Mostly useful for testing and demonstration purposes
      --verify-fn <VERIFY_FN>
          A Rust closure returning a bool that checks whether a regression reproduces. Example: `--verify-fn='|output| output.contains("internal compiler error")'`
      --env <ENV>
          Additional environment variables to pass to cargo/rustc. Example: `--env NAME=VALUE --env ANOTHER_NAME=VALUE`
      --project-dir <PROJECT_DIR>
          The working directory where cargo/rustc are invoked in. By default, this is the current working directory
      --script-path <SCRIPT_PATH>
          A path to a script that is run to check whether code reproduces. When it exits with code 0, the problem reproduces. If `--script-path-lints` isn't set, this script is also run to get lints. For lints, the `MINIMIZE_LINTS` environment variable will be set to `1`. The first line of the lint stdout or stderr can be `minimize-fmt-rustc` or `minimize-fmt-cargo` to show whether the rustc or wrapper cargo lint format and which output stream is used. Defaults to cargo and stdout
      --script-path-lints <SCRIPT_PATH_LINTS>
          A path to a script that is run to get lints. The first line of stdout or stderr must be `minimize-fmt-rustc` or `minimize-fmt-cargo` to show whether the rustc or wrapper cargo lint format and which output stream is used. Defaults to cargo and stdout
  -h, --help
          Print help information

Note: You can safely press Ctrl-C when running cargo-minimize. It will rollback the current minimization attempt and give you the latest known-reproducing state.

What it does

cargo-minimize is currently fairly simple. It does several passes over the source code. It treats each file in isolation. First, it applies the pass to everything in the file. If that stops the reproduction, it goes down the tree, eventually trying each candidate in isolation. It then repeats the pass until no more changes are made by it.

The currently implemented passes are the following:

• pub is replaced by pub(crate). This does not have a real minimization effect on its own.
• Bodies are replaced by loop {}. This greatly cuts down on the amount of things and makes many functions unused
• Unused imports are removed
• Unused functions are removed (this relies on the first step, as pub items are not marked as dead_code by rustc)

Possible improvements:

• Delete more kinds of unused items
• Inline small modules
• Deal with dependencies (there is experimental code in the repo that inlines them)
• Somehow deal with traits
• Integrate more fine-grained minimization tools such as DustMite or perses

Cookbook

Normal project with ICE on cargo build

cargo minimize

An environment variable is required

cargo minimize --env RUSTFLAGS=-Zpolymorphize

Operate on a single file

cargo minimize --rustc file.rs

Other cargo subcommand

cargo minimize --cargo-subcmd clippy --extra-args "-- -Dclippy::needless_mut"

Use a full script

script.sh

#!/usr/bin/env bash

# output minimize-fmt-cargo to stdout to indicate that cargo lints will be output to stdout
# this is the default
echo "minimize-fmt-cargo"

# The script needs to emit the output here for lints
cargo build --release
if [ $? = 128 ];
then
    echo "The ICE reproduces"
    exit 0
else
    echo "No reproduction"
    exit 1
fi

cargo minimize --script-path ./script.sh

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.