gccrs: add support for lang_item eq and PartialEq trait

The Eq and Partial Ord are very similar to the operator overloads
we support for add/sub/etc... but they differ in that usually the
function call name matches the name of the lang item. This time
we need to have support to send in a new path for the method call
on the lang item we want instead of just the name of the lang item.

NOTE: this test case doesnt work correctly yet we need to support
the derive of partial eq on enums to generate the correct comparison
code for that.

Fixes Rust-GCC#3302

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): handle partial_eq possible call
	* backend/rust-compile-expr.h: handle case where lang item calls differ from name
	* hir/tree/rust-hir-expr.cc (OperatorExprMeta::OperatorExprMeta): new helper
	* hir/tree/rust-hir-expr.h: likewise
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): handle partial_eq
	(TypeCheckExpr::resolve_operator_overload): likewise
	* typecheck/rust-hir-type-check-expr.h: likewise
	* util/rust-lang-item.cc (LangItem::ComparisonToLangItem): map comparison to lang item
	(LangItem::ComparisonToSegment): likewise
	* util/rust-lang-item.h: new lang items PartialOrd and Eq
	* util/rust-operators.h (enum class): likewise

gcc/testsuite/ChangeLog:

	* rust/compile/nr2/exclude: nr2 cant handle this
	* rust/compile/cmp1.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

2 files changed, 79 insertions, 0 deletions

diff --git a/gcc/testsuite/rust/compile/cmp1.rs b/gcc/testsuite/rust/compile/cmp1.rs
new file mode 100644
index 0000000..4da5b1c
--- /dev/null
+++ b/gcc/testsuite/rust/compile/cmp1.rs
@@ -0,0 +1,78 @@
+// { dg-options "-w" }
+// taken from https://github.com/rust-lang/rust/blob/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/core/src/cmp.rs#L98
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[lang = "eq"]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(alias = "==")]
+#[doc(alias = "!=")]
+pub trait PartialEq<Rhs: ?Sized = Self> {
+    /// This method tests for `self` and `other` values to be equal, and is used
+    /// by `==`.
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn eq(&self, other: &Rhs) -> bool;
+
+    /// This method tests for `!=`.
+    #[inline]
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn ne(&self, other: &Rhs) -> bool {
+        !self.eq(other)
+    }
+}
+
+enum BookFormat {
+    Paperback,
+    Hardback,
+    Ebook,
+}
+
+impl PartialEq<BookFormat> for BookFormat {
+    fn eq(&self, other: &BookFormat) -> bool {
+        self == other
+    }
+}
+
+pub struct Book {
+    isbn: i32,
+    format: BookFormat,
+}
+
+// Implement <Book> == <BookFormat> comparisons
+impl PartialEq<BookFormat> for Book {
+    fn eq(&self, other: &BookFormat) -> bool {
+        self.format == *other
+    }
+}
+
+// Implement <BookFormat> == <Book> comparisons
+impl PartialEq<Book> for BookFormat {
+    fn eq(&self, other: &Book) -> bool {
+        *self == other.format
+    }
+}
+
+// Implement <Book> == <Book> comparisons
+impl PartialEq<Book> for Book {
+    fn eq(&self, other: &Book) -> bool {
+        self.isbn == other.isbn
+    }
+}
+
+pub fn main() {
+    let b1 = Book {
+        isbn: 1,
+        format: BookFormat::Paperback,
+    };
+    let b2 = Book {
+        isbn: 2,
+        format: BookFormat::Paperback,
+    };
+
+    let _c1: bool = b1 == BookFormat::Paperback;
+    let _c2: bool = BookFormat::Paperback == b2;
+    let _c3: bool = b1 != b2;
+}
diff --git a/gcc/testsuite/rust/compile/nr2/exclude b/gcc/testsuite/rust/compile/nr2/exclude
index e7344ed..af7d105 100644
--- a/gcc/testsuite/rust/compile/nr2/exclude
+++ b/gcc/testsuite/rust/compile/nr2/exclude
@@ -196,4 +196,5 @@ additional-trait-bounds2.rs
 auto_traits2.rs
 auto_traits3.rs
 issue-3140.rs
+cmp1.rs
 # please don't delete the trailing newline