src/tools/clippy/clippy_lints/src/redundant_static_lifetimes.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::{meets_msrv, msrvs};
   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 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks for constants and statics with an explicit `'static` lifetime.
  13     ///
  14     /// ### Why is this bad?
  15     /// Adding `'static` to every reference can create very
  16     /// complicated types.
  17     ///
  18     /// ### Example
  19     /// ```ignore
  20     /// const FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  21     /// &[...]
  22     /// static FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  23     /// &[...]
  24     /// ```
  25     /// This code can be rewritten as
  26     /// ```ignore
  27     ///  const FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  28     ///  static FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  29     /// ```
  30     #[clippy::version = "1.37.0"]
  31     pub REDUNDANT_STATIC_LIFETIMES,
  32     style,
  33     "Using explicit `'static` lifetime for constants or statics when elision rules would allow omitting them."
  34 }
  35
  36 pub struct RedundantStaticLifetimes {
  37     msrv: Option<RustcVersion>,
  38 }
  39
  40 impl RedundantStaticLifetimes {
  41     #[must_use]
  42     pub fn new(msrv: Option<RustcVersion>) -> Self {
  43         Self { msrv }
  44     }
  45 }
  46
  47 impl_lint_pass!(RedundantStaticLifetimes => [REDUNDANT_STATIC_LIFETIMES]);
  48
  49 impl RedundantStaticLifetimes {
  50     // Recursively visit types
  51     fn visit_type(&mut self, ty: &Ty, cx: &EarlyContext<'_>, reason: &str) {
  52         match ty.kind {
  53             // Be careful of nested structures (arrays and tuples)
  54             TyKind::Array(ref ty, _) => {
  55                 self.visit_type(&*ty, cx, reason);
  56             },
  57             TyKind::Tup(ref tup) => {
  58                 for tup_ty in tup {
  59                     self.visit_type(&*tup_ty, cx, reason);
  60                 }
  61             },
  62             // This is what we are looking for !
  63             TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
  64                 // Match the 'static lifetime
  65                 if let Some(lifetime) = *optional_lifetime {
  66                     match borrow_type.ty.kind {
  67                         TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) | TyKind::Tup(..) => {
  68                             if lifetime.ident.name == rustc_span::symbol::kw::StaticLifetime {
  69                                 let snip = snippet(cx, borrow_type.ty.span, "<type>");
  70                                 let sugg = format!("&{}", snip);
  71                                 span_lint_and_then(
  72                                     cx,
  73                                     REDUNDANT_STATIC_LIFETIMES,
  74                                     lifetime.ident.span,
  75                                     reason,
  76                                     |diag| {
  77                                         diag.span_suggestion(
  78                                             ty.span,
  79                                             "consider removing `'static`",
  80                                             sugg,
  81                                             Applicability::MachineApplicable, //snippet
  82                                         );
  83                                     },
  84                                 );
  85                             }
  86                         },
  87                         _ => {},
  88                     }
  89                 }
  90                 self.visit_type(&*borrow_type.ty, cx, reason);
  91             },
  92             TyKind::Slice(ref ty) => {
  93                 self.visit_type(ty, cx, reason);
  94             },
  95             _ => {},
  96         }
  97     }
  98 }
  99
 100 impl EarlyLintPass for RedundantStaticLifetimes {
 101     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 102         if !meets_msrv(self.msrv.as_ref(), &msrvs::STATIC_IN_CONST) {
 103             return;
 104         }
 105
 106         if !item.span.from_expansion() {
 107             if let ItemKind::Const(_, ref var_type, _) = item.kind {
 108                 self.visit_type(var_type, cx, "constants have by default a `'static` lifetime");
 109                 // Don't check associated consts because `'static` cannot be elided on those (issue
 110                 // #2438)
 111             }
 112
 113             if let ItemKind::Static(ref var_type, _, _) = item.kind {
 114                 self.visit_type(var_type, cx, "statics have by default a `'static` lifetime");
 115             }
 116         }
 117     }
 118
 119     extract_msrv_attr!(EarlyContext);
 120 }