# cargo-minimize

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

For more info, see the [cookbook](https://github.com/Noratrieb/cargo-minimize#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`](https://github.com/uw-pluverse/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`

```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](LICENSE-APACHE) or https://www.apache.org/licenses/LICENSE-2.0)
- MIT license ([LICENSE-MIT](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.