Dylint
A tool for running Rust lints from dynamic libraries
cargo install cargo-dylint dylint-linkDylint is a Rust linting tool, similar to Clippy. But whereas Clippy runs a predetermined, static set of lints, Dylint runs lints from user-specified, dynamic libraries. Thus, Dylint allows developers to maintain their own personal lint collections.
Contents
Documentation is also available on how Dylint works.
Quick start
Running Dylint
The next three steps install Dylint and run all of this repository's general-purpose, example lints on a workspace:
-
Install
cargo-dylintanddylint-link:cargo install cargo-dylint dylint-link
-
Add the following to the workspace's
Cargo.tomlfile:[workspace.metadata.dylint] libraries = [ { git = "https://github.com/trailofbits/dylint", pattern = "examples/general/*" }, ]
-
Run
cargo-dylint:cargo dylint --all --workspace
In the above example, the libraries are found via workspace metadata, which is the recommended way. For additional ways of finding libraries, see How Dylint works.
Writing lints
You can start writing your own Dylint library by running cargo dylint new new_lint_name. Doing so will produce a loadable library right out of the box. You can verify this as follows:
cargo dylint new new_lint_name
cd new_lint_name
cargo build
DYLINT_LIBRARY_PATH=$PWD/target/debug cargo dylint list --lib new_lint_nameAll you have to do is implement the LateLintPass trait and accommodate the symbols asking to be filled in.
Helpful resources for writing lints appear below.
Features
Workspace metadata
A workspace can name the libraries it should be linted with in its Cargo.toml file. Specifically, a workspace's manifest can contain a TOML list under workspace.metadata.dylint.libraries. Each list entry must have the form of a Cargo git or path dependency, with the following differences:
- There is no leading package name, i.e., no
package =. pathentries can contain glob patterns, e.g.,*.- Any entry can contain a
patternfield whose value is a glob pattern. Thepatternfield indicates the subdirectories that contain Dylint libraries.
Dylint downloads and builds each entry, similar to how Cargo downloads and builds a dependency. The resulting target/release directories are searched for files with names of the form that Dylint recognizes (see Library requirements under How Dylint works).
As an example, if you include the following in your workspace's Cargo.toml file and run cargo dylint --all --workspace, Dylint will run on your workspace all of this repository's example general-purpose lints, as well as the example restriction lint try_io_result.
[workspace.metadata.dylint]
libraries = [
{ git = "https://github.com/trailofbits/dylint", pattern = "examples/general/*" },
{ git = "https://github.com/trailofbits/dylint", pattern = "examples/restriction/try_io_result" },
]Configurable libraries
Libraries can be configured by including a dylint.toml file in a linted workspace's root directory. The file should encode a toml table whose keys are library names. A library determines how its value in the table (if any) is interpreted.
As an example, a dylint.toml file with the following contents sets the non_local_effect_before_error_return library's work_limit configuration to 1_000_000:
[non_local_effect_before_error_return]
work_limit = 1_000_000For instructions on creating a configurable library, see the dylint_linting documentation.
Conditional compilation
For each library that Dylint uses to check a crate, Dylint passes the following to the Rust compiler:
--cfg=dylint_lib="LIBRARY_NAME"You can use this feature to allow a lint when Dylint is used, but also avoid an "unknown lint" warning when Dylint is not used. Specifically, you can do the following:
#[cfg_attr(dylint_lib = "LIBRARY_NAME", allow(LINT_NAME))]Note that LIBRARY_NAME and LINT_NAME may be the same. For an example involving non_thread_safe_call_in_test, see dylint/src/lib.rs in this repository.
Also note that the just described approach does not work for pre-expansion lints. The only known workaround for pre-expansion lints is allow the compiler's built-in unknown_lints lint. Specifically, you can do the following:
#[allow(unknown_lints)]
#[allow(PRE_EXPANSION_LINT_NAME)]For an example involving env_cargo_path, see internal/src/examples.rs in this repository.
VS Code integration
Dylint results can be viewed in VS Code using rust-analyzer. To do so, add the following to your VS Code settings.json file:
"rust-analyzer.checkOnSave.overrideCommand": [
"cargo",
"dylint",
"--all",
"--workspace",
"--",
"--all-targets",
"--message-format=json"
]If you want to use rust-analyzer inside a lint library, you need to add the following to your VS Code settings.json file:
"rust-analyzer.rustc.source": "discover",And add the following to the library's Cargo.toml file:
[package.metadata.rust-analyzer]
rustc_private = trueUtilities
The following utilities can be helpful for writing Dylint libraries:
dylint-linkis a wrapper around Rust's default linker (cc) that creates a copy of your library with a filename that Dylint recognizes.dylint_library!is a macro that automatically defines thedylint_versionfunction and adds theextern crate rustc_driverdeclaration.ui_testis a function that can be used to test Dylint libraries. It provides convenient access to thecompiletest_rspackage.clippy_utilsis a collection of utilities to make writing lints easier. It is generously made public by the Rust Clippy Developers. Note that, likerustc,clippy_utilsprovides no stability guarantees for its APIs.
Resources
Helpful resources for writing lints include the following:
- Adding a new lint (targeted at Clippy but still useful)
- Author lint
- Common tools for writing lints
- Guide to Rustc Development
- Crate
rustc_hir - Crate
rustc_middle - Struct
rustc_lint::LateContext