clippy_lints/src/const_static_lifetime.rs

   1 use syntax::ast::{Item, ItemKind, TyKind, Ty};
   2 use rustc::lint::{LintPass, EarlyLintPass, LintArray, EarlyContext};
   3 use utils::{span_lint_and_then, in_macro};
   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) => {
  45                 for tup_ty in tup {
  46                     self.visit_type(&*tup_ty, cx);
  47                 }
  48             },
  49             // This is what we are looking for !
  50             TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
  51                 // Match the 'static lifetime
  52                 if let Some(lifetime) = *optional_lifetime {
  53                     if let TyKind::Path(_, _) = borrow_type.ty.node {
  54                         // Verify that the path is a str
  55                         if lifetime.ident.name == "'static" {
  56                             let mut sug: String = String::new();
  57                             span_lint_and_then(cx,
  58                                                CONST_STATIC_LIFETIME,
  59                                                lifetime.span,
  60                                                "Constants have by default a `'static` lifetime",
  61                                                |db| {db.span_suggestion(lifetime.span,"consider removing `'static`",sug);});
  62                         }
  63                     }
  64                 }
  65                 self.visit_type(&*borrow_type.ty, cx);
  66             },
  67             TyKind::Slice(ref ty) => {
  68                 self.visit_type(ty, cx);
  69             },
  70             _ => {},
  71         }
  72     }
  73 }
  74
  75 impl EarlyLintPass for StaticConst {
  76     fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
  77         if !in_macro(item.span) {
  78             // Match only constants...
  79             if let ItemKind::Const(ref var_type, _) = item.node {
  80                 self.visit_type(var_type, cx);
  81             }
  82         }
  83     }
  84 }