clippy_lints/src/const_static_lifetime.rs

   1 use syntax::ast::{Item, ItemKind, Ty, TyKind};
   2 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
   3 use utils::{in_macro, span_lint_and_then};
   4
   5 /// **What it does:** Checks for constants with an explicit `'static` lifetime.
   6 ///
   7 /// **Why is this bad?** Adding `'static` to every reference can create very
   8 /// complicated types.
   9 ///
  10 /// **Known problems:** None.
  11 ///
  12 /// **Example:**
  13 /// ```rust
  14 /// const FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  15 /// &[...]
  16 /// ```
  17 /// This code can be rewritten as
  18 /// ```rust
  19 ///  const FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  20 /// ```
  21
  22 declare_lint! {
  23     pub CONST_STATIC_LIFETIME,
  24     Warn,
  25     "Using explicit `'static` lifetime for constants when elision rules would allow omitting them."
  26 }
  27
  28 pub struct StaticConst;
  29
  30 impl LintPass for StaticConst {
  31     fn get_lints(&self) -> LintArray {
  32         lint_array!(CONST_STATIC_LIFETIME)
  33     }
  34 }
  35
  36 impl StaticConst {
  37     // Recursively visit types
  38     fn visit_type(&mut self, ty: &Ty, cx: &EarlyContext) {
  39         match ty.node {
  40             // Be careful of nested structures (arrays and tuples)
  41             TyKind::Array(ref ty, _) => {
  42                 self.visit_type(&*ty, cx);
  43             },
  44             TyKind::Tup(ref tup) => for tup_ty in tup {
  45                 self.visit_type(&*tup_ty, cx);
  46             },
  47             // This is what we are looking for !
  48             TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
  49                 // Match the 'static lifetime
  50                 if let Some(lifetime) = *optional_lifetime {
  51                     if let TyKind::Path(_, _) = borrow_type.ty.node {
  52                         // Verify that the path is a str
  53                         if lifetime.ident.name == "'static" {
  54                             let mut sug: String = String::new();
  55                             span_lint_and_then(
  56                                 cx,
  57                                 CONST_STATIC_LIFETIME,
  58                                 lifetime.span,
  59                                 "Constants have by default a `'static` lifetime",
  60                                 |db| {
  61                                     db.span_suggestion(lifetime.span, "consider removing `'static`", sug);
  62                                 },
  63                             );
  64                         }
  65                     }
  66                 }
  67                 self.visit_type(&*borrow_type.ty, cx);
  68             },
  69             TyKind::Slice(ref ty) => {
  70                 self.visit_type(ty, cx);
  71             },
  72             _ => {},
  73         }
  74     }
  75 }
  76
  77 impl EarlyLintPass for StaticConst {
  78     fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
  79         if !in_macro(item.span) {
  80             // Match only constants...
  81             if let ItemKind::Const(ref var_type, _) = item.node {
  82                 self.visit_type(var_type, cx);
  83             }
  84         }
  85     }
  86 }