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

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::msrvs::{self, 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_session::{declare_tool_lint, impl_lint_pass};
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Checks for constants and statics with an explicit `'static` lifetime.
  12     ///
  13     /// ### Why is this bad?
  14     /// Adding `'static` to every reference can create very
  15     /// complicated types.
  16     ///
  17     /// ### Example
  18     /// ```ignore
  19     /// const FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  20     /// &[...]
  21     /// static FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
  22     /// &[...]
  23     /// ```
  24     /// This code can be rewritten as
  25     /// ```ignore
  26     ///  const FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  27     ///  static FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
  28     /// ```
  29     #[clippy::version = "1.37.0"]
  30     pub REDUNDANT_STATIC_LIFETIMES,
  31     style,
  32     "Using explicit `'static` lifetime for constants or statics when elision rules would allow omitting them."
  33 }
  34
  35 pub struct RedundantStaticLifetimes {
  36     msrv: Msrv,
  37 }
  38
  39 impl RedundantStaticLifetimes {
  40     #[must_use]
  41     pub fn new(msrv: Msrv) -> Self {
  42         Self { msrv }
  43     }
  44 }
  45
  46 impl_lint_pass!(RedundantStaticLifetimes => [REDUNDANT_STATIC_LIFETIMES]);
  47
  48 impl RedundantStaticLifetimes {
  49     // Recursively visit types
  50     fn visit_type(ty: &Ty, cx: &EarlyContext<'_>, reason: &str) {
  51         match ty.kind {
  52             // Be careful of nested structures (arrays and tuples)
  53             TyKind::Array(ref ty, _) | TyKind::Slice(ref ty) => {
  54                 Self::visit_type(ty, cx, reason);
  55             },
  56             TyKind::Tup(ref tup) => {
  57                 for tup_ty in tup {
  58                     Self::visit_type(tup_ty, cx, reason);
  59                 }
  60             },
  61             // This is what we are looking for !
  62             TyKind::Ref(ref optional_lifetime, ref borrow_type) => {
  63                 // Match the 'static lifetime
  64                 if let Some(lifetime) = *optional_lifetime {
  65                     match borrow_type.ty.kind {
  66                         TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) | TyKind::Tup(..) => {
  67                             if lifetime.ident.name == rustc_span::symbol::kw::StaticLifetime {
  68                                 let snip = snippet(cx, borrow_type.ty.span, "<type>");
  69                                 let sugg = format!("&{}{snip}", borrow_type.mutbl.prefix_str());
  70                                 span_lint_and_then(
  71                                     cx,
  72                                     REDUNDANT_STATIC_LIFETIMES,
  73                                     lifetime.ident.span,
  74                                     reason,
  75                                     |diag| {
  76                                         diag.span_suggestion(
  77                                             ty.span,
  78                                             "consider removing `'static`",
  79                                             sugg,
  80                                             Applicability::MachineApplicable, //snippet
  81                                         );
  82                                     },
  83                                 );
  84                             }
  85                         },
  86                         _ => {},
  87                     }
  88                 }
  89                 Self::visit_type(&borrow_type.ty, cx, reason);
  90             },
  91             _ => {},
  92         }
  93     }
  94 }
  95
  96 impl EarlyLintPass for RedundantStaticLifetimes {
  97     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
  98         if !self.msrv.meets(msrvs::STATIC_IN_CONST) {
  99             return;
 100         }
 101
 102         if !item.span.from_expansion() {
 103             if let ItemKind::Const(_, ref var_type, _) = item.kind {
 104                 Self::visit_type(var_type, cx, "constants have by default a `'static` lifetime");
 105                 // Don't check associated consts because `'static` cannot be elided on those (issue
 106                 // #2438)
 107             }
 108
 109             if let ItemKind::Static(ref var_type, _, _) = item.kind {
 110                 Self::visit_type(var_type, cx, "statics have by default a `'static` lifetime");
 111             }
 112         }
 113     }
 114
 115     extract_msrv_attr!(EarlyContext);
 116 }