2018-04-19 19:34:31 +00:00
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use super::utils::{get_arg_name, match_var, remove_blocks, snippet, span_lint_and_sugg};
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use rustc::hir::*;
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use rustc::lint::*;
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/// **What it does:** Checks for matches being used to destructure a single-variant enum
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/// or tuple struct where a `let` will suffice.
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///
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/// **Why is this bad?** Just readability – `let` doesn't nest, whereas a `match` does.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// enum Wrapper {
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/// Data(i32),
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/// }
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///
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/// let wrapper = Wrapper::Data(42);
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///
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/// let data = match wrapper {
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/// Wrapper::Data(i) => i,
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/// };
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/// ```
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///
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/// The correct use would be:
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/// ```rust
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/// enum Wrapper {
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/// Data(i32),
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/// }
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///
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/// let wrapper = Wrapper::Data(42);
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/// let Wrapper::Data(data) = wrapper;
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/// ```
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declare_clippy_lint! {
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pub INFALLIBLE_DESTRUCTURING_MATCH,
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style,
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"a match statement with a single infallible arm instead of a `let`"
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}
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#[derive(Copy, Clone, Default)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(INFALLIBLE_DESTRUCTURING_MATCH)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_local(&mut self, cx: &LateContext<'a, 'tcx>, local: &'tcx Local) {
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if_chain! {
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if let Some(ref expr) = local.init;
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2018-07-12 07:30:57 +00:00
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if let ExprKind::Match(ref target, ref arms, MatchSource::Normal) = expr.node;
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2018-04-19 19:34:31 +00:00
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if arms.len() == 1 && arms[0].pats.len() == 1 && arms[0].guard.is_none();
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if let PatKind::TupleStruct(QPath::Resolved(None, ref variant_name), ref args, _) = arms[0].pats[0].node;
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if args.len() == 1;
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if let Some(arg) = get_arg_name(&args[0]);
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let body = remove_blocks(&arms[0].body);
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if match_var(body, arg);
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then {
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span_lint_and_sugg(
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cx,
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INFALLIBLE_DESTRUCTURING_MATCH,
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local.span,
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"you seem to be trying to use match to destructure a single infallible pattern. \
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Consider using `let`",
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"try this",
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format!(
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"let {}({}) = {};",
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snippet(cx, variant_name.span, ".."),
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snippet(cx, local.pat.span, ".."),
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snippet(cx, target.span, ".."),
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),
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);
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}
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}
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}
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}
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