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| 1 | +use crate::utils::span_lint_and_help; |
| 2 | + |
| 3 | +use rustc_hir::{CaptureBy, Expr, ExprKind, PatKind}; |
| 4 | +use rustc_lint::{LateContext, LateLintPass}; |
| 5 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 6 | + |
| 7 | +declare_clippy_lint! { |
| 8 | + /// **What it does:** Checks for instances of `map_err(|_| Some::Enum)` |
| 9 | + /// |
| 10 | + /// **Why is this bad?** This map_err throws away the original error rather than allowing the enum to contain and report the cause of the error |
| 11 | + /// |
| 12 | + /// **Known problems:** None. |
| 13 | + /// |
| 14 | + /// **Example:** |
| 15 | + /// Before: |
| 16 | + /// ```rust |
| 17 | + /// use std::fmt; |
| 18 | + /// |
| 19 | + /// #[derive(Debug)] |
| 20 | + /// enum Error { |
| 21 | + /// Indivisible, |
| 22 | + /// Remainder(u8), |
| 23 | + /// } |
| 24 | + /// |
| 25 | + /// impl fmt::Display for Error { |
| 26 | + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 27 | + /// match self { |
| 28 | + /// Error::Indivisible => write!(f, "could not divide input by three"), |
| 29 | + /// Error::Remainder(remainder) => write!( |
| 30 | + /// f, |
| 31 | + /// "input is not divisible by three, remainder = {}", |
| 32 | + /// remainder |
| 33 | + /// ), |
| 34 | + /// } |
| 35 | + /// } |
| 36 | + /// } |
| 37 | + /// |
| 38 | + /// impl std::error::Error for Error {} |
| 39 | + /// |
| 40 | + /// fn divisible_by_3(input: &str) -> Result<(), Error> { |
| 41 | + /// input |
| 42 | + /// .parse::<i32>() |
| 43 | + /// .map_err(|_| Error::Indivisible) |
| 44 | + /// .map(|v| v % 3) |
| 45 | + /// .and_then(|remainder| { |
| 46 | + /// if remainder == 0 { |
| 47 | + /// Ok(()) |
| 48 | + /// } else { |
| 49 | + /// Err(Error::Remainder(remainder as u8)) |
| 50 | + /// } |
| 51 | + /// }) |
| 52 | + /// } |
| 53 | + /// ``` |
| 54 | + /// |
| 55 | + /// After: |
| 56 | + /// ```rust |
| 57 | + /// use std::{fmt, num::ParseIntError}; |
| 58 | + /// |
| 59 | + /// #[derive(Debug)] |
| 60 | + /// enum Error { |
| 61 | + /// Indivisible(ParseIntError), |
| 62 | + /// Remainder(u8), |
| 63 | + /// } |
| 64 | + /// |
| 65 | + /// impl fmt::Display for Error { |
| 66 | + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 67 | + /// match self { |
| 68 | + /// Error::Indivisible(_) => write!(f, "could not divide input by three"), |
| 69 | + /// Error::Remainder(remainder) => write!( |
| 70 | + /// f, |
| 71 | + /// "input is not divisible by three, remainder = {}", |
| 72 | + /// remainder |
| 73 | + /// ), |
| 74 | + /// } |
| 75 | + /// } |
| 76 | + /// } |
| 77 | + /// |
| 78 | + /// impl std::error::Error for Error { |
| 79 | + /// fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { |
| 80 | + /// match self { |
| 81 | + /// Error::Indivisible(source) => Some(source), |
| 82 | + /// _ => None, |
| 83 | + /// } |
| 84 | + /// } |
| 85 | + /// } |
| 86 | + /// |
| 87 | + /// fn divisible_by_3(input: &str) -> Result<(), Error> { |
| 88 | + /// input |
| 89 | + /// .parse::<i32>() |
| 90 | + /// .map_err(Error::Indivisible) |
| 91 | + /// .map(|v| v % 3) |
| 92 | + /// .and_then(|remainder| { |
| 93 | + /// if remainder == 0 { |
| 94 | + /// Ok(()) |
| 95 | + /// } else { |
| 96 | + /// Err(Error::Remainder(remainder as u8)) |
| 97 | + /// } |
| 98 | + /// }) |
| 99 | + /// } |
| 100 | + /// ``` |
| 101 | + pub MAP_ERR_IGNORE, |
| 102 | + pedantic, |
| 103 | + "`map_err` should not ignore the original error" |
| 104 | +} |
| 105 | + |
| 106 | +declare_lint_pass!(MapErrIgnore => [MAP_ERR_IGNORE]); |
| 107 | + |
| 108 | +impl<'tcx> LateLintPass<'tcx> for MapErrIgnore { |
| 109 | + // do not try to lint if this is from a macro or desugaring |
| 110 | + fn check_expr(&mut self, cx: &LateContext<'_>, e: &Expr<'_>) { |
| 111 | + if e.span.from_expansion() { |
| 112 | + return; |
| 113 | + } |
| 114 | + |
| 115 | + // check if this is a method call (e.g. x.foo()) |
| 116 | + if let ExprKind::MethodCall(ref method, _t_span, ref args, _) = e.kind { |
| 117 | + // only work if the method name is `map_err` and there are only 2 arguments (e.g. x.map_err(|_|[1] |
| 118 | + // Enum::Variant[2])) |
| 119 | + if method.ident.as_str() == "map_err" && args.len() == 2 { |
| 120 | + // make sure the first argument is a closure, and grab the CaptureRef, body_id, and body_span fields |
| 121 | + if let ExprKind::Closure(capture, _, body_id, body_span, _) = args[1].kind { |
| 122 | + // check if this is by Reference (meaning there's no move statement) |
| 123 | + if capture == CaptureBy::Ref { |
| 124 | + // Get the closure body to check the parameters and values |
| 125 | + let closure_body = cx.tcx.hir().body(body_id); |
| 126 | + // make sure there's only one parameter (`|_|`) |
| 127 | + if closure_body.params.len() == 1 { |
| 128 | + // make sure that parameter is the wild token (`_`) |
| 129 | + if let PatKind::Wild = closure_body.params[0].pat.kind { |
| 130 | + // span the area of the closure capture and warn that the |
| 131 | + // original error will be thrown away |
| 132 | + span_lint_and_help( |
| 133 | + cx, |
| 134 | + MAP_ERR_IGNORE, |
| 135 | + body_span, |
| 136 | + "`map_err(|_|...` ignores the original error", |
| 137 | + None, |
| 138 | + "Consider wrapping the error in an enum variant", |
| 139 | + ); |
| 140 | + } |
| 141 | + } |
| 142 | + } |
| 143 | + } |
| 144 | + } |
| 145 | + } |
| 146 | + } |
| 147 | +} |
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