use super::utils::{get_arg_name, match_var, remove_blocks, snippet, span_lint_and_sugg}; use rustc::hir::*; use rustc::lint::*; /// **What it does:** Checks for matches being used to destructure a single-variant enum /// or tuple struct where a `let` will suffice. /// /// **Why is this bad?** Just readability – `let` doesn't nest, whereas a `match` does. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// enum Wrapper { /// Data(i32), /// } /// /// let wrapper = Wrapper::Data(42); /// /// let data = match wrapper { /// Wrapper::Data(i) => i, /// }; /// ``` /// /// The correct use would be: /// ```rust /// enum Wrapper { /// Data(i32), /// } /// /// let wrapper = Wrapper::Data(42); /// let Wrapper::Data(data) = wrapper; /// ``` declare_clippy_lint! { pub INFALLIBLE_DESTRUCTURING_MATCH, style, "a match statement with a single infallible arm instead of a `let`" } #[derive(Copy, Clone, Default)] pub struct Pass; impl LintPass for Pass { fn get_lints(&self) -> LintArray { lint_array!(INFALLIBLE_DESTRUCTURING_MATCH) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { fn check_local(&mut self, cx: &LateContext<'a, 'tcx>, local: &'tcx Local) { if_chain! { if let Some(ref expr) = local.init; if let Expr_::ExprMatch(ref target, ref arms, MatchSource::Normal) = expr.node; if arms.len() == 1 && arms[0].pats.len() == 1 && arms[0].guard.is_none(); if let PatKind::TupleStruct(QPath::Resolved(None, ref variant_name), ref args, _) = arms[0].pats[0].node; if args.len() == 1; if let Some(arg) = get_arg_name(&args[0]); let body = remove_blocks(&arms[0].body); if match_var(body, arg); then { span_lint_and_sugg( cx, INFALLIBLE_DESTRUCTURING_MATCH, local.span, "you seem to be trying to use match to destructure a single infallible pattern. \ Consider using `let`", "try this", format!( "let {}({}) = {};", snippet(cx, variant_name.span, ".."), snippet(cx, local.pat.span, ".."), snippet(cx, target.span, ".."), ), ); } } } }