How to pass rustc flags to cargo?

Question

You can pass flags through Cargo by several different means:

• cargo rustc, which only affects your crate and not its dependencies.
• The RUSTFLAGS environment variable, which affects dependencies as well.
• Some flags have a proper Cargo option, e.g., -C lto and -C panic=abort can be specified in the Cargo.toml file.
• Add flags in .cargo/config using one of the rustflags= keys.

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However, in your specific case of configuring lints, you don't need to use compiler flags; you can also enable and disable lints directly in the source code using attributes. This may in fact be a better option as it's more robust, more targeted, and doesn't require you to alter your build system setup:

#![deny(some_lint)] // deny lint in this module and its children

#[allow(another_lint)] // allow lint in this function
fn foo() {
    ...
}

See also:

• How to disable unused code warnings in Rust?