1 files changed, 60 insertions, 0 deletions
diff --git a/src/librustc_middle/middle/lang_items.rs b/src/librustc_middle/middle/lang_items.rs
new file mode 100644
index 00000000000..0f98c338c16
--- /dev/null
+++ b/src/librustc_middle/middle/lang_items.rs
@@ -0,0 +1,60 @@
+//! Detecting language items.
+//!
+//! Language items are items that represent concepts intrinsic to the language
+//! itself. Examples are:
+//!
+//! * Traits that specify "kinds"; e.g., `Sync`, `Send`.
+//! * Traits that represent operators; e.g., `Add`, `Sub`, `Index`.
+//! * Functions called by the compiler itself.
+
+use crate::ty::{self, TyCtxt};
+
+use rustc_hir::def_id::DefId;
+use rustc_hir::LangItem;
+use rustc_span::Span;
+use rustc_target::spec::PanicStrategy;
+
+impl<'tcx> TyCtxt<'tcx> {
+    /// Returns the `DefId` for a given `LangItem`.
+    /// If not found, fatally aborts compilation.
+    pub fn require_lang_item(&self, lang_item: LangItem, span: Option<Span>) -> DefId {
+        self.lang_items().require(lang_item).unwrap_or_else(|msg| {
+            if let Some(span) = span {
+                self.sess.span_fatal(span, &msg)
+            } else {
+                self.sess.fatal(&msg)
+            }
+        })
+    }
+
+    pub fn fn_trait_kind_from_lang_item(&self, id: DefId) -> Option<ty::ClosureKind> {
+        let items = self.lang_items();
+        match Some(id) {
+            x if x == items.fn_trait() => Some(ty::ClosureKind::Fn),
+            x if x == items.fn_mut_trait() => Some(ty::ClosureKind::FnMut),
+            x if x == items.fn_once_trait() => Some(ty::ClosureKind::FnOnce),
+            _ => None,
+        }
+    }
+
+    pub fn is_weak_lang_item(&self, item_def_id: DefId) -> bool {
+        self.lang_items().is_weak_lang_item(item_def_id)
+    }
+}
+
+/// Returns `true` if the specified `lang_item` doesn't actually need to be
+/// present for this compilation.
+///
+/// Not all lang items are always required for each compilation, particularly in
+/// the case of panic=abort. In these situations some lang items are injected by
+/// crates and don't actually need to be defined in libstd.
+pub fn whitelisted(tcx: TyCtxt<'_>, lang_item: LangItem) -> bool {
+    // If we're not compiling with unwinding, we won't actually need these
+    // symbols. Other panic runtimes ensure that the relevant symbols are
+    // available to link things together, but they're never exercised.
+    if tcx.sess.panic_strategy() != PanicStrategy::Unwind {
+        return lang_item == LangItem::EhPersonalityLangItem;
+    }
+
+    false
+}