gccrs: ast: Add base for desugaring try expressions

gcc/rust/ChangeLog:

	* Make-lang.in: Compile it.
	* ast/rust-desugar-question-mark.cc: New file.
	* ast/rust-desugar-question-mark.h: New file.

gcc/testsuite/ChangeLog:

	* rust/compile/try-expr1.rs: New test.

1 files changed, 84 insertions, 0 deletions

diff --git a/gcc/testsuite/rust/compile/try-expr1.rs b/gcc/testsuite/rust/compile/try-expr1.rs
new file mode 100644
index 0000000..f1a7865
--- /dev/null
+++ b/gcc/testsuite/rust/compile/try-expr1.rs
@@ -0,0 +1,84 @@
+// { dg-additional-options "-frust-compile-until=typecheck" }
+
+#[lang = "sized"]
+trait Sized {}
+
+enum Result {
+    #[lang = "Ok"]
+    Ok(i32),
+    #[lang = "Err"]
+    Err(i32)
+}
+
+pub trait From<T>: Sized {
+    /// Performs the conversion.
+    #[lang = "from"]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn from(_: T) -> Self;
+}
+
+impl<T> From<T> for T {
+    fn from(t: T) -> Self { t }
+}
+
+#[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;
+
+    /// 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: i32) -> 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: i32) -> Self;
+}
+
+impl Try for Result {
+    // type Ok = i32;
+    // type Error = i32;
+
+    fn into_result(self) -> Result {
+        self
+    }
+
+    fn from_ok(v: i32) -> Self {
+        Result::Ok(v)
+    }
+
+    fn from_error(v: i32) -> Self {
+        Result::Err(v)
+    }
+}
+
+fn bar() -> Result {
+    Result::Ok(15)
+}
+
+fn foo() -> Result {
+    let a = bar()?;
+
+    Result::Ok(a)
+}