rulewright 0.1.2

Executable engineering standards for Rust workspaces
Documentation 
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use ra_ap_syntax::ast::{self, HasName};

use crate::{AstCtx, Example, Violation};

#[rustfmt::skip]
const EXAMPLES: &[Example] = &[
    Example {
        label: "as_ takes self by value",
        code: "struct S;\nimpl S {\n    fn as_str(self) {}\n}",
        pass: false,
    },
    Example {
        label: "to_ takes self by value",
        code: "struct S;\nimpl S {\n    fn to_vec(self) {}\n}",
        pass: false,
    },
    Example {
        label: "into_ borrows self",
        code: "struct S;\nimpl S {\n    fn into_parts(&self) {}\n}",
        pass: false,
    },
    Example {
        label: "into_ borrows self mutably",
        code: "struct S;\nimpl S {\n    fn into_inner(&mut self) {}\n}",
        pass: false,
    },
    Example {
        label: "wrong convention on trait method",
        code: "trait T {\n    fn as_bytes(self);\n}",
        pass: false,
    },
    Example {
        label: "as_ borrows",
        code: "struct S;\nimpl S {\n    fn as_str(&self) {}\n}",
        pass: true,
    },
    Example {
        label: "as_ borrows mutably",
        code: "struct S;\nimpl S {\n    fn as_mut_slice(&mut self) {}\n}",
        pass: true,
    },
    Example {
        label: "to_ borrows",
        code: "struct S;\nimpl S {\n    fn to_vec(&self) {}\n}",
        pass: true,
    },
    Example {
        label: "into_ consumes",
        code: "struct S;\nimpl S {\n    fn into_parts(self) {}\n}",
        pass: true,
    },
    Example {
        label: "no receiver is exempt",
        code: "struct S;\nimpl S {\n    fn into_config() -> S { S }\n}",
        pass: true,
    },
    Example {
        label: "non-conversion method",
        code: "struct S;\nimpl S {\n    fn assemble(self) {}\n}",
        pass: true,
    },
    Example {
        label: "wrong convention in test module",
        code: "#[cfg(test)]\nmod tests {\n    struct S;\n    impl S {\n        fn as_str(self) {}\n    }\n}",
        pass: true,
    },
];

crate::ast_rule!(
    conversion_self_convention,
    "Enforce C-CONV receivers: `as_`/`to_` methods borrow (`&self`), `into_` methods consume (`self`).",
    "The `as_`/`to_`/`into_` prefixes promise a cost and ownership contract; a consuming `to_` or borrowing `into_` misleads every caller.",
    Medium,
);

fn check_conversion_self_convention(ctx: &AstCtx<'_>) -> Vec<Violation> {
    ctx.nodes::<ast::Fn>()
        .filter(|function| !ctx.is_in_test(function))
        .filter_map(|function| {
            let receiver = function.param_list()?.self_param()?;

            if receiver.colon_token().is_some() {
                return None;
            }

            let name = function.name()?;
            let name_text = name.text();
            let borrows = receiver.amp_token().is_some();
            let message = if (name_text.starts_with("as_") || name_text.starts_with("to_"))
                && !borrows
            {
                format!(
                    "conversion `{name_text}` consumes `self` — `as_`/`to_` methods take `&self`; use `into_` for consuming conversions (C-CONV)"
                )
            } else if name_text.starts_with("into_") && borrows {
                format!(
                    "conversion `{name_text}` borrows `self` — `into_` methods consume `self` by value (C-CONV)"
                )
            } else {
                return None;
            };

            Some(ctx.violation(&name, message))
        })
        .collect()
}

crate::rulewright_ast_test!(check_conversion_self_convention, {
    crate::example_tests!(EXAMPLES, check_conversion_self_convention);
});