compiler/rustc_middle/src/middle/lang_items.rs

   1 //! Detecting language items.
   2 //!
   3 //! Language items are items that represent concepts intrinsic to the language
   4 //! itself. Examples are:
   5 //!
   6 //! * Traits that specify "kinds"; e.g., `Sync`, `Send`.
   7 //! * Traits that represent operators; e.g., `Add`, `Sub`, `Index`.
   8 //! * Functions called by the compiler itself.
   9
  10 use crate::ty::{self, TyCtxt};
  11
  12 use rustc_hir::def_id::DefId;
  13 use rustc_hir::LangItem;
  14 use rustc_span::Span;
  15 use rustc_target::spec::PanicStrategy;
  16
  17 impl<'tcx> TyCtxt<'tcx> {
  18     /// Returns the `DefId` for a given `LangItem`.
  19     /// If not found, fatally aborts compilation.
  20     pub fn require_lang_item(self, lang_item: LangItem, span: Option<Span>) -> DefId {
  21         self.lang_items().require(lang_item).unwrap_or_else(|err| {
  22             if let Some(span) = span {
  23                 self.sess.span_fatal(span, err.to_string())
  24             } else {
  25                 self.sess.fatal(err.to_string())
  26             }
  27         })
  28     }
  29
  30     /// Given a [`DefId`] of a [`Fn`], [`FnMut`] or [`FnOnce`] traits,
  31     /// returns a corresponding [`ty::ClosureKind`].
  32     /// For any other [`DefId`] return `None`.
  33     pub fn fn_trait_kind_from_def_id(self, id: DefId) -> Option<ty::ClosureKind> {
  34         let items = self.lang_items();
  35         match Some(id) {
  36             x if x == items.fn_trait() => Some(ty::ClosureKind::Fn),
  37             x if x == items.fn_mut_trait() => Some(ty::ClosureKind::FnMut),
  38             x if x == items.fn_once_trait() => Some(ty::ClosureKind::FnOnce),
  39             _ => None,
  40         }
  41     }
  42
  43     /// Returns `true` if `id` is a `DefId` of [`Fn`], [`FnMut`] or [`FnOnce`] traits.
  44     pub fn is_fn_trait(self, id: DefId) -> bool {
  45         self.fn_trait_kind_from_def_id(id).is_some()
  46     }
  47 }
  48
  49 /// Returns `true` if the specified `lang_item` must be present for this
  50 /// compilation.
  51 ///
  52 /// Not all lang items are always required for each compilation, particularly in
  53 /// the case of panic=abort. In these situations some lang items are injected by
  54 /// crates and don't actually need to be defined in libstd.
  55 pub fn required(tcx: TyCtxt<'_>, lang_item: LangItem) -> bool {
  56     // If we're not compiling with unwinding, we won't actually need these
  57     // symbols. Other panic runtimes ensure that the relevant symbols are
  58     // available to link things together, but they're never exercised.
  59     match tcx.sess.panic_strategy() {
  60         PanicStrategy::Abort => {
  61             lang_item != LangItem::EhPersonality && lang_item != LangItem::EhCatchTypeinfo
  62         }
  63         PanicStrategy::Unwind => true,
  64     }
  65 }