From ffb17d0aed31448827590ddd3a1268e0a823534f Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Sat, 18 Dec 2021 02:07:52 +0000
Subject: [PATCH] Support Option<()> (and &Option<()>) incl conversion and
 printing

---
 c-bindings-gen/src/blocks.rs | 25 ++++++++++++++++++-------
 c-bindings-gen/src/types.rs  | 16 +++++++++++++++-
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/c-bindings-gen/src/blocks.rs b/c-bindings-gen/src/blocks.rs
index 6e6b897..b2f952b 100644
--- a/c-bindings-gen/src/blocks.rs
+++ b/c-bindings-gen/src/blocks.rs
@@ -346,27 +346,38 @@ pub fn write_option_block<W: std::io::Write>(w: &mut W, mangled_container: &str,
 	writeln!(w, "/// An enum which can either contain a {} or not", inner_type).unwrap();
 	writeln!(w, "pub enum {} {{", mangled_container).unwrap();
 	writeln!(w, "\t/// When we're in this state, this {} contains a {}", mangled_container, inner_type).unwrap();
-	writeln!(w, "\tSome({}),", inner_type).unwrap();
+	if inner_type != "" {
+		writeln!(w, "\tSome({}),", inner_type).unwrap();
+	} else {
+		writeln!(w, "\tSome,").unwrap();
+	}
 	writeln!(w, "\t/// When we're in this state, this {} contains nothing", mangled_container).unwrap();
 	writeln!(w, "\tNone").unwrap();
 	writeln!(w, "}}").unwrap();
 
 	writeln!(w, "impl {} {{", mangled_container).unwrap();
 	writeln!(w, "\t#[allow(unused)] pub(crate) fn is_some(&self) -> bool {{").unwrap();
-	writeln!(w, "\t\tif let Self::Some(_) = self {{ true }} else {{ false }}").unwrap();
+	writeln!(w, "\t\tif let Self::None = self {{ false }} else {{ true }}").unwrap();
 	writeln!(w, "\t}}").unwrap();
 	writeln!(w, "\t#[allow(unused)] pub(crate) fn is_none(&self) -> bool {{").unwrap();
 	writeln!(w, "\t\t!self.is_some()").unwrap();
 	writeln!(w, "\t}}").unwrap();
-	writeln!(w, "\t#[allow(unused)] pub(crate) fn take(mut self) -> {} {{", inner_type).unwrap();
-	writeln!(w, "\t\tif let Self::Some(v) = self {{ v }} else {{ unreachable!() }}").unwrap();
-	writeln!(w, "\t}}").unwrap();
+	if inner_type != "" {
+		writeln!(w, "\t#[allow(unused)] pub(crate) fn take(mut self) -> {} {{", inner_type).unwrap();
+		writeln!(w, "\t\tif let Self::Some(v) = self {{ v }} else {{ unreachable!() }}").unwrap();
+		writeln!(w, "\t}}").unwrap();
+	}
 	writeln!(w, "}}").unwrap();
 
 	writeln!(w, "#[no_mangle]").unwrap();
 	writeln!(w, "/// Constructs a new {} containing a {}", mangled_container, inner_type).unwrap();
-	writeln!(w, "pub extern \"C\" fn {}_some(o: {}) -> {} {{", mangled_container, inner_type, mangled_container).unwrap();
-	writeln!(w, "\t{}::Some(o)", mangled_container).unwrap();
+	if inner_type != "" {
+		writeln!(w, "pub extern \"C\" fn {}_some(o: {}) -> {} {{", mangled_container, inner_type, mangled_container).unwrap();
+		writeln!(w, "\t{}::Some(o)", mangled_container).unwrap();
+	} else {
+		writeln!(w, "pub extern \"C\" fn {}_some() -> {} {{", mangled_container, mangled_container).unwrap();
+		writeln!(w, "\t{}::Some", mangled_container).unwrap();
+	}
 	writeln!(w, "}}").unwrap();
 
 	writeln!(w, "#[no_mangle]").unwrap();
diff --git a/c-bindings-gen/src/types.rs b/c-bindings-gen/src/types.rs
index 5fc90b1..0a6bce4 100644
--- a/c-bindings-gen/src/types.rs
+++ b/c-bindings-gen/src/types.rs
@@ -1386,6 +1386,14 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 					}
 				}
 				if let Some(t) = single_contained {
+					if let syn::Type::Tuple(syn::TypeTuple { elems, .. }) = t {
+						assert!(elems.is_empty());
+						let inner_name = self.get_c_mangled_container_type(vec![single_contained.unwrap()], generics, "Option").unwrap();
+						return Some(("if ", vec![
+							(format!(".is_none() {{ {}::None }} else {{ {}::Some /*",
+								inner_name, inner_name), format!(""))
+							], " */}", ContainerPrefixLocation::PerConv));
+					}
 					if let syn::Type::Reference(syn::TypeReference { elem, .. }) = t {
 						if let syn::Type::Slice(_) = &**elem {
 							return Some(("if ", vec![
@@ -2393,7 +2401,13 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 				}
 				if !self.write_c_type_intern(w, t, generics, false, false, false, false) { return false; }
 			} else {
-				assert!(!is_ref); // We don't currently support outer reference types for non-primitive inners
+				// We don't currently support outer reference types for non-primitive inners,
+				// except for the empty tuple.
+				if let syn::Type::Tuple(t_arg) = t {
+					assert!(t_arg.elems.len() == 0 || !is_ref);
+				} else {
+					assert!(!is_ref);
+				}
 				if !self.write_c_type_intern(w, t, generics, false, false, false, false) { return false; }
 			}
 		}
-- 
2.30.2