src/tools/clippy/clippy_lints/src/unused_label.rs

   1 use rustc::lint::*;
   2 use rustc::hir;
   3 use rustc::hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
   4 use std::collections::HashMap;
   5 use syntax::ast;
   6 use syntax::codemap::Span;
   7 use syntax::symbol::InternedString;
   8 use utils::{in_macro, span_lint};
   9
  10 /// **What it does:** Checks for unused labels.
  11 ///
  12 /// **Why is this bad?** Maybe the label should be used in which case there is
  13 /// an error in the code or it should be removed.
  14 ///
  15 /// **Known problems:** Hopefully none.
  16 ///
  17 /// **Example:**
  18 /// ```rust,ignore
  19 /// fn unused_label() {
  20 ///     'label: for i in 1..2 {
  21 ///         if i > 4 { continue }
  22 ///     }
  23 /// ```
  24 declare_lint! {
  25     pub UNUSED_LABEL,
  26     Warn,
  27     "unused labels"
  28 }
  29
  30 pub struct UnusedLabel;
  31
  32 struct UnusedLabelVisitor<'a, 'tcx: 'a> {
  33     labels: HashMap<InternedString, Span>,
  34     cx: &'a LateContext<'a, 'tcx>,
  35 }
  36
  37 impl LintPass for UnusedLabel {
  38     fn get_lints(&self) -> LintArray {
  39         lint_array!(UNUSED_LABEL)
  40     }
  41 }
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedLabel {
  44     fn check_fn(
  45         &mut self,
  46         cx: &LateContext<'a, 'tcx>,
  47         kind: FnKind<'tcx>,
  48         decl: &'tcx hir::FnDecl,
  49         body: &'tcx hir::Body,
  50         span: Span,
  51         fn_id: ast::NodeId,
  52     ) {
  53         if in_macro(span) {
  54             return;
  55         }
  56
  57         let mut v = UnusedLabelVisitor {
  58             cx: cx,
  59             labels: HashMap::new(),
  60         };
  61         walk_fn(&mut v, kind, decl, body.id(), span, fn_id);
  62
  63         for (label, span) in v.labels {
  64             span_lint(cx, UNUSED_LABEL, span, &format!("unused label `{}`", label));
  65         }
  66     }
  67 }
  68
  69 impl<'a, 'tcx: 'a> Visitor<'tcx> for UnusedLabelVisitor<'a, 'tcx> {
  70     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
  71         match expr.node {
  72             hir::ExprBreak(destination, _) | hir::ExprAgain(destination) => if let Some(label) = destination.ident {
  73                 self.labels.remove(&label.node.name.as_str());
  74             },
  75             hir::ExprLoop(_, Some(label), _) | hir::ExprWhile(_, _, Some(label)) => {
  76                 self.labels.insert(label.node.as_str(), expr.span);
  77             },
  78             _ => (),
  79         }
  80
  81         walk_expr(self, expr);
  82     }
  83     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  84         NestedVisitorMap::All(&self.cx.tcx.hir)
  85     }
  86 }