rulewright 0.1.1

Executable engineering standards for Rust workspaces
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70

use ra_ap_syntax::{AstNode, ast, ast::HasArgList};

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

#[rustfmt::skip]
const EXAMPLES: &[Example] = &[
    Example {
        label: "wildcard discard",
        code: r#"fn f() { let _ = Ok::<i32, i32>(1).map_err(|_| "bad"); }"#,
        pass: false,
    },
    Example {
        label: "named param",
        code: r#"fn f() { let _ = Ok::<i32, i32>(1).map_err(|e| format!("{e}")); }"#,
        pass: true,
    },
    Example {
        label: "underscore-prefixed param",
        code: r#"fn f() { let _ = Ok::<i32, i32>(1).map_err(|_e| "bad"); }"#,
        pass: false,
    },
    Example {
        label: "function ref",
        code: "fn f() { let _ = Ok::<i32, String>(1).map_err(String::from); }",
        pass: true,
    },
    Example {
        label: "discard in test module",
        code: "#[cfg(test)]\nmod tests {\n    fn t() { let _ = Ok::<i32, i32>(1).map_err(|_| \"bad\"); }\n}",
        pass: true,
    },
];

crate::ast_rule!(
    missing_error_context,
    "Flag `.map_err(|_| ...)` that discards the original error.",
    "Discarding the original error in map_err(|_| ...) destroys the root cause, making failures hard to diagnose.",
    Medium,
);

fn check_missing_error_context(ctx: &AstCtx<'_>) -> Vec<Violation> {
    ctx.nodes::<ast::MethodCallExpr>()
        .filter(|call| !ctx.is_in_test(call))
        .filter_map(|call| {
            let method = call.name_ref()?;

            if method.text() != "map_err" {
                return None;
            }

            let closure = call.arg_list()?.args().next().and_then(|arg| match arg {
                ast::Expr::ClosureExpr(closure) => Some(closure),
                _ => None,
            })?;
            let param = closure.param_list()?.syntax().text().to_string();
            let binding = param.trim().trim_matches('|').trim();

            (binding == "_" || binding.starts_with('_')).then(|| {
                ctx.violation(
                    &method,
                    ".map_err(|_| ...) discards the original error — use the error variable",
                )
            })
        })
        .collect()
}

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