src/tools/clippy/clippy_lints/src/missing_inline.rs

   1 use clippy_utils::diagnostics::span_lint;
   2 use rustc_ast::ast;
   3 use rustc_hir as hir;
   4 use rustc_lint::{self, LateContext, LateLintPass, LintContext};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6 use rustc_span::source_map::Span;
   7 use rustc_span::sym;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** it lints if an exported function, method, trait method with default impl,
  11     /// or trait method impl is not `#[inline]`.
  12     ///
  13     /// **Why is this bad?** In general, it is not. Functions can be inlined across
  14     /// crates when that's profitable as long as any form of LTO is used. When LTO is disabled,
  15     /// functions that are not `#[inline]` cannot be inlined across crates. Certain types of crates
  16     /// might intend for most of the methods in their public API to be able to be inlined across
  17     /// crates even when LTO is disabled. For these types of crates, enabling this lint might make
  18     /// sense. It allows the crate to require all exported methods to be `#[inline]` by default, and
  19     /// then opt out for specific methods where this might not make sense.
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     /// ```rust
  25     /// pub fn foo() {} // missing #[inline]
  26     /// fn ok() {} // ok
  27     /// #[inline] pub fn bar() {} // ok
  28     /// #[inline(always)] pub fn baz() {} // ok
  29     ///
  30     /// pub trait Bar {
  31     ///   fn bar(); // ok
  32     ///   fn def_bar() {} // missing #[inline]
  33     /// }
  34     ///
  35     /// struct Baz;
  36     /// impl Baz {
  37     ///    fn private() {} // ok
  38     /// }
  39     ///
  40     /// impl Bar for Baz {
  41     ///   fn bar() {} // ok - Baz is not exported
  42     /// }
  43     ///
  44     /// pub struct PubBaz;
  45     /// impl PubBaz {
  46     ///    fn private() {} // ok
  47     ///    pub fn not_ptrivate() {} // missing #[inline]
  48     /// }
  49     ///
  50     /// impl Bar for PubBaz {
  51     ///    fn bar() {} // missing #[inline]
  52     ///    fn def_bar() {} // missing #[inline]
  53     /// }
  54     /// ```
  55     pub MISSING_INLINE_IN_PUBLIC_ITEMS,
  56     restriction,
  57     "detects missing `#[inline]` attribute for public callables (functions, trait methods, methods...)"
  58 }
  59
  60 fn check_missing_inline_attrs(cx: &LateContext<'_>, attrs: &[ast::Attribute], sp: Span, desc: &'static str) {
  61     let has_inline = attrs.iter().any(|a| a.has_name(sym::inline));
  62     if !has_inline {
  63         span_lint(
  64             cx,
  65             MISSING_INLINE_IN_PUBLIC_ITEMS,
  66             sp,
  67             &format!("missing `#[inline]` for {}", desc),
  68         );
  69     }
  70 }
  71
  72 fn is_executable_or_proc_macro(cx: &LateContext<'_>) -> bool {
  73     use rustc_session::config::CrateType;
  74
  75     cx.tcx
  76         .sess
  77         .crate_types()
  78         .iter()
  79         .any(|t: &CrateType| matches!(t, CrateType::Executable | CrateType::ProcMacro))
  80 }
  81
  82 declare_lint_pass!(MissingInline => [MISSING_INLINE_IN_PUBLIC_ITEMS]);
  83
  84 impl<'tcx> LateLintPass<'tcx> for MissingInline {
  85     fn check_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx hir::Item<'_>) {
  86         if rustc_middle::lint::in_external_macro(cx.sess(), it.span) || is_executable_or_proc_macro(cx) {
  87             return;
  88         }
  89
  90         if !cx.access_levels.is_exported(it.hir_id()) {
  91             return;
  92         }
  93         match it.kind {
  94             hir::ItemKind::Fn(..) => {
  95                 let desc = "a function";
  96                 let attrs = cx.tcx.hir().attrs(it.hir_id());
  97                 check_missing_inline_attrs(cx, attrs, it.span, desc);
  98             },
  99             hir::ItemKind::Trait(ref _is_auto, ref _unsafe, ref _generics, _bounds, trait_items) => {
 100                 // note: we need to check if the trait is exported so we can't use
 101                 // `LateLintPass::check_trait_item` here.
 102                 for tit in trait_items {
 103                     let tit_ = cx.tcx.hir().trait_item(tit.id);
 104                     match tit_.kind {
 105                         hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(..) => {},
 106                         hir::TraitItemKind::Fn(..) => {
 107                             if tit.defaultness.has_value() {
 108                                 // trait method with default body needs inline in case
 109                                 // an impl is not provided
 110                                 let desc = "a default trait method";
 111                                 let item = cx.tcx.hir().trait_item(tit.id);
 112                                 let attrs = cx.tcx.hir().attrs(item.hir_id());
 113                                 check_missing_inline_attrs(cx, attrs, item.span, desc);
 114                             }
 115                         },
 116                     }
 117                 }
 118             },
 119             hir::ItemKind::Const(..)
 120             | hir::ItemKind::Enum(..)
 121             | hir::ItemKind::Mod(..)
 122             | hir::ItemKind::Static(..)
 123             | hir::ItemKind::Struct(..)
 124             | hir::ItemKind::TraitAlias(..)
 125             | hir::ItemKind::GlobalAsm(..)
 126             | hir::ItemKind::TyAlias(..)
 127             | hir::ItemKind::Union(..)
 128             | hir::ItemKind::OpaqueTy(..)
 129             | hir::ItemKind::ExternCrate(..)
 130             | hir::ItemKind::ForeignMod { .. }
 131             | hir::ItemKind::Impl { .. }
 132             | hir::ItemKind::Use(..) => {},
 133         };
 134     }
 135
 136     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
 137         use rustc_middle::ty::{ImplContainer, TraitContainer};
 138         if rustc_middle::lint::in_external_macro(cx.sess(), impl_item.span) || is_executable_or_proc_macro(cx) {
 139             return;
 140         }
 141
 142         // If the item being implemented is not exported, then we don't need #[inline]
 143         if !cx.access_levels.is_exported(impl_item.hir_id()) {
 144             return;
 145         }
 146
 147         let desc = match impl_item.kind {
 148             hir::ImplItemKind::Fn(..) => "a method",
 149             hir::ImplItemKind::Const(..) | hir::ImplItemKind::TyAlias(_) => return,
 150         };
 151
 152         let trait_def_id = match cx.tcx.associated_item(impl_item.def_id).container {
 153             TraitContainer(cid) => Some(cid),
 154             ImplContainer(cid) => cx.tcx.impl_trait_ref(cid).map(|t| t.def_id),
 155         };
 156
 157         if let Some(trait_def_id) = trait_def_id {
 158             if trait_def_id.is_local() && !cx.access_levels.is_exported(impl_item.hir_id()) {
 159                 // If a trait is being implemented for an item, and the
 160                 // trait is not exported, we don't need #[inline]
 161                 return;
 162             }
 163         }
 164
 165         let attrs = cx.tcx.hir().attrs(impl_item.hir_id());
 166         check_missing_inline_attrs(cx, attrs, impl_item.span, desc);
 167     }
 168 }