clippy_lints/src/redundant_static_lifetimes.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::meets_msrv;
   3 use clippy_utils::source::snippet;
   4 use rustc_ast::ast::{Item, ItemKind, Ty, TyKind};
   5 use rustc_errors::Applicability;
   6 use rustc_lint::{EarlyContext, EarlyLintPass};
   7 use rustc_semver::RustcVersion;
   8 use rustc_session::{declare_tool_lint, impl_lint_pass};
   9
  10 const REDUNDANT_STATIC_LIFETIMES_MSRV: RustcVersion = RustcVersion::new(1, 17, 0);
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for constants and statics with an explicit `'static` lifetime.
  14     ///
  15     /// **Why is this bad?** Adding `'static` to every reference can create very
  16     /// complicated types.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```ignore
  22     /// const FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  23     /// &[...]
  24     /// static FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  25     /// &[...]
  26     /// ```
  27     /// This code can be rewritten as
  28     /// ```ignore
  29     ///  const FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  30     ///  static FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  31     /// ```
  32     pub REDUNDANT_STATIC_LIFETIMES,
  33     style,
  34     "Using explicit `'static` lifetime for constants or statics when elision rules would allow omitting them."
  35 }
  36
  37 pub struct RedundantStaticLifetimes {
  38     msrv: Option<RustcVersion>,
  39 }
  40
  41 impl RedundantStaticLifetimes {
  42     #[must_use]
  43     pub fn new(msrv: Option<RustcVersion>) -> Self {
  44         Self { msrv }
  45     }
  46 }
  47
  48 impl_lint_pass!(RedundantStaticLifetimes => [REDUNDANT_STATIC_LIFETIMES]);
  49
  50 impl RedundantStaticLifetimes {
  51     // Recursively visit types
  52     fn visit_type(&mut self, ty: &Ty, cx: &EarlyContext<'_>, reason: &str) {
  53         match ty.kind {
  54             // Be careful of nested structures (arrays and tuples)
  55             TyKind::Array(ref ty, _) => {
  56                 self.visit_type(&*ty, cx, reason);
  57             },
  58             TyKind::Tup(ref tup) => {
  59                 for tup_ty in tup {
  60                     self.visit_type(&*tup_ty, cx, reason);
  61                 }
  62             },
  63             // This is what we are looking for !
  64             TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
  65                 // Match the 'static lifetime
  66                 if let Some(lifetime) = *optional_lifetime {
  67                     match borrow_type.ty.kind {
  68                         TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) | TyKind::Tup(..) => {
  69                             if lifetime.ident.name == rustc_span::symbol::kw::StaticLifetime {
  70                                 let snip = snippet(cx, borrow_type.ty.span, "<type>");
  71                                 let sugg = format!("&{}", snip);
  72                                 span_lint_and_then(
  73                                     cx,
  74                                     REDUNDANT_STATIC_LIFETIMES,
  75                                     lifetime.ident.span,
  76                                     reason,
  77                                     |diag| {
  78                                         diag.span_suggestion(
  79                                             ty.span,
  80                                             "consider removing `'static`",
  81                                             sugg,
  82                                             Applicability::MachineApplicable, //snippet
  83                                         );
  84                                     },
  85                                 );
  86                             }
  87                         },
  88                         _ => {},
  89                     }
  90                 }
  91                 self.visit_type(&*borrow_type.ty, cx, reason);
  92             },
  93             TyKind::Slice(ref ty) => {
  94                 self.visit_type(ty, cx, reason);
  95             },
  96             _ => {},
  97         }
  98     }
  99 }
 100
 101 impl EarlyLintPass for RedundantStaticLifetimes {
 102     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 103         if !meets_msrv(self.msrv.as_ref(), &REDUNDANT_STATIC_LIFETIMES_MSRV) {
 104             return;
 105         }
 106
 107         if !item.span.from_expansion() {
 108             if let ItemKind::Const(_, ref var_type, _) = item.kind {
 109                 self.visit_type(var_type, cx, "constants have by default a `'static` lifetime");
 110                 // Don't check associated consts because `'static` cannot be elided on those (issue
 111                 // #2438)
 112             }
 113
 114             if let ItemKind::Static(ref var_type, _, _) = item.kind {
 115                 self.visit_type(var_type, cx, "statics have by default a `'static` lifetime");
 116             }
 117         }
 118     }
 119
 120     extract_msrv_attr!(EarlyContext);
 121 }