lang-items: Add Result and Try lang items

gcc/rust/ChangeLog:

	* util/rust-lang-item.h: Add handling for Result::Ok, Result::Err, Try, Try::into_result,
	Try::from_ok, Try::from_err.
	* util/rust-lang-item.cc: Likewise.

gcc/testsuite/ChangeLog:

	* rust/compile/try-trait.rs: New test.

gcc/rust/util/rust-lang-item.cc

@@ -97,11 +97,19 @@ const BiMap<std::string, LangItem::Kind> Rust::LangItem::lang_items = {{
   {"Some", Kind::OPTION_SOME},
   {"None", Kind::OPTION_NONE},
 
+  {"Ok", Kind::RESULT_OK},
+  {"Err", Kind::RESULT_ERR},
+
   {"into_iter", Kind::INTOITER_INTOITER},
   {"next", Kind::ITERATOR_NEXT},
 
   {"eq", Kind::EQ},
   {"partial_ord", Kind::PARTIAL_ORD},
+
+  {"try", Kind::TRY},
+  {"into_result", Kind::TRY_INTO_RESULT},
+  {"from_error", Kind::TRY_FROM_ERROR},
+  {"from_ok", Kind::TRY_FROM_OK},
 }};
 
 tl::optional<LangItem::Kind>

gcc/rust/util/rust-lang-item.h

@@ -127,8 +127,20 @@ class LangItem
     OPTION_SOME,
     OPTION_NONE,
 
+    RESULT_OK,
+    RESULT_ERR,
+
     INTOITER_INTOITER,
     ITERATOR_NEXT,
+
+    // NOTE: These lang items are *not* necessarily present in later versions of
+    // Rust (I am unsure at which point they have been removed as the `Try`
+    // trait is unstable). They will need to be changed when updating the
+    // targeted Rust version of gccrs
+    TRY,
+    TRY_INTO_RESULT,
+    TRY_FROM_ERROR,
+    TRY_FROM_OK,
   };
 
   static const BiMap<std::string, Kind> lang_items;

gcc/testsuite/rust/compile/try-trait.rs

@@ -0,0 +1,44 @@
+#[lang = "sized"]
+trait Sized {}
+
+enum Result<T, E> {
+    #[lang = "Ok"]
+    Ok(T),
+    #[lang = "Err"]
+    Err(E)
+}
+
+#[lang = "try"]
+pub trait Try {
+    /// The type of this value when viewed as successful.
+    #[unstable(feature = "try_trait", issue = "42327")]
+    type Ok;
+    /// The type of this value when viewed as failed.
+    #[unstable(feature = "try_trait", issue = "42327")]
+    type Error;
+
+    /// Applies the "?" operator. A return of `Ok(t)` means that the
+    /// execution should continue normally, and the result of `?` is the
+    /// value `t`. A return of `Err(e)` means that execution should branch
+    /// to the innermost enclosing `catch`, or return from the function.
+    ///
+    /// If an `Err(e)` result is returned, the value `e` will be "wrapped"
+    /// in the return type of the enclosing scope (which must itself implement
+    /// `Try`). Specifically, the value `X::from_error(From::from(e))`
+    /// is returned, where `X` is the return type of the enclosing function.
+    #[lang = "into_result"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn into_result(self) -> Result<Self::Ok, Self::Error>;
+
+    /// Wrap an error value to construct the composite result. For example,
+    /// `Result::Err(x)` and `Result::from_error(x)` are equivalent.
+    #[lang = "from_error"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn from_error(v: Self::Error) -> Self;
+
+    /// Wrap an OK value to construct the composite result. For example,
+    /// `Result::Ok(x)` and `Result::from_ok(x)` are equivalent.
+    #[lang = "from_ok"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn from_ok(v: Self::Ok) -> Self;
+}