diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/map_err_ignore.rs')
| -rw-r--r-- | src/tools/clippy/clippy_lints/src/map_err_ignore.rs | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/map_err_ignore.rs b/src/tools/clippy/clippy_lints/src/map_err_ignore.rs new file mode 100644 index 000000000..21d0e19eb --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/map_err_ignore.rs @@ -0,0 +1,154 @@ +use clippy_utils::diagnostics::span_lint_and_help; +use rustc_hir::{CaptureBy, Closure, 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 contain and report the cause of the error + /// + /// ### 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)) + /// } + /// }) + /// } + /// ``` + #[clippy::version = "1.48.0"] + pub MAP_ERR_IGNORE, + restriction, + "`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(method, 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, BodyId, and fn_decl_span + // fields + if let ExprKind::Closure(&Closure { + capture_clause, + body, + fn_decl_span, + .. + }) = args[1].kind + { + // check if this is by Reference (meaning there's no move statement) + if capture_clause == CaptureBy::Ref { + // Get the closure body to check the parameters and values + let closure_body = cx.tcx.hir().body(body); + // 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, + fn_decl_span, + "`map_err(|_|...` wildcard pattern discards the original error", + None, + "consider storing the original error as a source in the new error, or silence this warning using an ignored identifier (`.map_err(|_foo| ...`)", + ); + } + } + } + } + } + } + } +} |