forked from rust-lang/rust
/
map_err_ignore.rs
147 lines (142 loc) · 5.31 KB
/
map_err_ignore.rs
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
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
use crate::utils::span_lint_and_help;
use rustc_hir::{CaptureBy, Expr, ExprKind, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for instances of `map_err(|_| Some::Enum)`
///
/// **Why is this bad?** This map_err throws away the original error rather than allowing the enum to bubble the original error
///
/// **Known problems:** None.
///
/// **Example:**
/// Before:
/// ```rust
/// use std::fmt;
///
/// #[derive(Debug)]
/// enum Error {
/// Indivisible,
/// Remainder(u8),
/// }
///
/// impl fmt::Display for Error {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// match self {
/// Error::Indivisible => write!(f, "could not divide input by three"),
/// Error::Remainder(remainder) => write!(
/// f,
/// "input is not divisible by three, remainder = {}",
/// remainder
/// ),
/// }
/// }
/// }
///
/// impl std::error::Error for Error {}
///
/// fn divisible_by_3(input: &str) -> Result<(), Error> {
/// input
/// .parse::<i32>()
/// .map_err(|_| Error::Indivisible)
/// .map(|v| v % 3)
/// .and_then(|remainder| {
/// if remainder == 0 {
/// Ok(())
/// } else {
/// Err(Error::Remainder(remainder as u8))
/// }
/// })
/// }
/// ```
///
/// After:
/// ```rust
/// use std::{fmt, num::ParseIntError};
///
/// #[derive(Debug)]
/// enum Error {
/// Indivisible(ParseIntError),
/// Remainder(u8),
/// }
///
/// impl fmt::Display for Error {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// match self {
/// Error::Indivisible(_) => write!(f, "could not divide input by three"),
/// Error::Remainder(remainder) => write!(
/// f,
/// "input is not divisible by three, remainder = {}",
/// remainder
/// ),
/// }
/// }
/// }
///
/// impl std::error::Error for Error {
/// fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
/// match self {
/// Error::Indivisible(source) => Some(source),
/// _ => None,
/// }
/// }
/// }
///
/// fn divisible_by_3(input: &str) -> Result<(), Error> {
/// input
/// .parse::<i32>()
/// .map_err(Error::Indivisible)
/// .map(|v| v % 3)
/// .and_then(|remainder| {
/// if remainder == 0 {
/// Ok(())
/// } else {
/// Err(Error::Remainder(remainder as u8))
/// }
/// })
/// }
/// ```
pub MAP_ERR_IGNORE,
style,
"`map_err` should not ignore the original error"
}
declare_lint_pass!(MapErrIgnore => [MAP_ERR_IGNORE]);
impl<'tcx> LateLintPass<'tcx> for MapErrIgnore {
// do not try to lint if this is from a macro or desugaring
fn check_expr(&mut self, cx: &LateContext<'_>, e: &Expr<'_>) {
if e.span.from_expansion() {
return;
}
// check if this is a method call (e.g. x.foo())
if let ExprKind::MethodCall(ref method, _t_span, ref args, _) = e.kind {
// only work if the method name is `map_err` and there are only 2 arguments (e.g. x.map_err(|_|[1]
// Enum::Variant[2]))
if method.ident.as_str() == "map_err" && args.len() == 2 {
// make sure the first argument is a closure, and grab the CaptureRef, body_id, and body_span fields
if let ExprKind::Closure(capture, _, body_id, body_span, _) = args[1].kind {
// check if this is by Reference (meaning there's no move statement)
if capture == CaptureBy::Ref {
// Get the closure body to check the parameters and values
let closure_body = cx.tcx.hir().body(body_id);
// make sure there's only one parameter (`|_|`)
if closure_body.params.len() == 1 {
// make sure that parameter is the wild token (`_`)
if let PatKind::Wild = closure_body.params[0].pat.kind {
// span the area of the closure capture and warn that the
// original error will be thrown away
span_lint_and_help(
cx,
MAP_ERR_IGNORE,
body_span,
"`map_else(|_|...` ignores the original error",
None,
"Consider wrapping the error in an enum variant",
);
}
}
}
}
}
}
}
}