Add a *Ref struct for traits and Deref to it rather than Self

Because LDK often takes `Deref<Target=Trait>` as type parameters,
we'd implemented `Deref { type Target=Self; .. }` for the traits
defined in the bindings crate. This worked well, but because Rust
auto-`Deref`s, it can lead to spurious compilation failures due to
infinite recursion trying to deref.

In the past we've worked around this by coming up with alternative
compilation strategies when faced with `Deref` recursion, but we
don't strictly need to.

Instead, here, we introduce duplicates of all our `Trait` structs
which become the `Deref` `Target`. This way, we can `Deref` into
the `Trait` and maintain LDK compatibility, without having any
infinite `Deref` recursion issues.

One complication is traits which contain associated types to define
`Deref`s to another associated type, e.g.

trait A {
    type B;
    type C: Deref<Target = Self::B>;
}

In this case, `B` needs to be the `TraitRef` and `C` needs to be
the `Trait`. We add code specifically to detect this case.

Author: TheBlueMatt

c-bindings-gen/src/main.rs

@@ -225,6 +225,11 @@ fn do_write_impl_trait<W: std::io::Write>(w: &mut W, trait_path: &str, _trait_na
 			writeln!(w, "\t\tlet vec = (self.write)(self.this_arg);").unwrap();
 			writeln!(w, "\t\tw.write_all(vec.as_slice())").unwrap();
 			writeln!(w, "\t}}\n}}").unwrap();
+			writeln!(w, "impl {} for {}Ref {{", trait_path, for_obj).unwrap();
+			writeln!(w, "\tfn write<W: lightning::util::ser::Writer>(&self, w: &mut W) -> Result<(), crate::c_types::io::Error> {{").unwrap();
+			writeln!(w, "\t\tlet vec = (self.0.write)(self.0.this_arg);").unwrap();
+			writeln!(w, "\t\tw.write_all(vec.as_slice())").unwrap();
+			writeln!(w, "\t}}\n}}").unwrap();
 		},
 		_ => panic!(),
 	}
@@ -450,6 +455,47 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 		($t: expr, $impl_accessor: expr, $type_resolver: expr, $generic_impls: expr) => {
 			let mut trait_gen_types = gen_types.push_ctx();
 			assert!(trait_gen_types.learn_generics_with_impls(&$t.generics, $generic_impls, $type_resolver));
+
+			let mut ref_types = HashSet::new();
+			for item in $t.items.iter() {
+				if let syn::TraitItem::Type(ref t) = &item {
+					if t.default.is_some() || t.generics.lt_token.is_some() { panic!("10"); }
+					let mut bounds_iter = t.bounds.iter();
+					loop {
+						match bounds_iter.next().unwrap() {
+							syn::TypeParamBound::Trait(tr) => {
+								match $type_resolver.resolve_path(&tr.path, None).as_str() {
+									"core::ops::Deref"|"core::ops::DerefMut"|"std::ops::Deref"|"std::ops::DerefMut" => {
+										// Handle cases like
+										// trait A {
+										//  type B;
+										//  type C: Deref<Target = Self::B>;
+										// }
+										// by tracking if we have any B's here and making them
+										// the *Ref types below.
+										if let syn::PathArguments::AngleBracketed(args) = &tr.path.segments.iter().last().unwrap().arguments {
+											if let syn::GenericArgument::Binding(bind) = args.args.iter().last().unwrap() {
+												assert_eq!(format!("{}", bind.ident), "Target");
+												if let syn::Type::Path(p) = &bind.ty {
+													assert!(p.qself.is_none());
+													let mut segs = p.path.segments.iter();
+													assert_eq!(format!("{}", segs.next().unwrap().ident), "Self");
+													ref_types.insert(format!("{}", segs.next().unwrap().ident));
+													assert!(segs.next().is_none());
+												} else { panic!(); }
+											}
+										}
+									},
+									_ => {},
+								}
+								break;
+							}
+							syn::TypeParamBound::Lifetime(_) => {},
+						}
+					}
+				}
+			}
+
 			for item in $t.items.iter() {
 				match item {
 					syn::TraitItem::Method(m) => {
@@ -538,7 +584,11 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 						loop {
 							match bounds_iter.next().unwrap() {
 								syn::TypeParamBound::Trait(tr) => {
-									writeln!(w, "\ttype {} = crate::{};", t.ident, $type_resolver.resolve_path(&tr.path, Some(&gen_types))).unwrap();
+									write!(w, "\ttype {} = crate::{}", t.ident, $type_resolver.resolve_path(&tr.path, Some(&gen_types))).unwrap();
+									if ref_types.contains(&format!("{}", t.ident)) {
+										write!(w, "Ref").unwrap();
+									}
+									writeln!(w, ";").unwrap();
 									for bound in bounds_iter {
 										if let syn::TypeParamBound::Trait(t) = bound {
 											// We only allow for `Sized` here.
@@ -581,10 +631,15 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 			writeln!(w, "impl core::cmp::Eq for {} {{}}", trait_name).unwrap();
 			writeln!(w, "impl core::cmp::PartialEq for {} {{", trait_name).unwrap();
 			writeln!(w, "\tfn eq(&self, o: &Self) -> bool {{ (self.eq)(self.this_arg, o) }}\n}}").unwrap();
+			writeln!(w, "impl core::cmp::Eq for {}Ref {{}}", trait_name).unwrap();
+			writeln!(w, "impl core::cmp::PartialEq for {}Ref {{", trait_name).unwrap();
+			writeln!(w, "\tfn eq(&self, o: &Self) -> bool {{ (self.0.eq)(self.0.this_arg, &o.0) }}\n}}").unwrap();
 		},
 		("std::hash::Hash", _, _)|("core::hash::Hash", _, _) => {
 			writeln!(w, "impl core::hash::Hash for {} {{", trait_name).unwrap();
 			writeln!(w, "\tfn hash<H: core::hash::Hasher>(&self, hasher: &mut H) {{ hasher.write_u64((self.hash)(self.this_arg)) }}\n}}").unwrap();
+			writeln!(w, "impl core::hash::Hash for {}Ref {{", trait_name).unwrap();
+			writeln!(w, "\tfn hash<H: core::hash::Hasher>(&self, hasher: &mut H) {{ hasher.write_u64((self.0.hash)(self.0.this_arg)) }}\n}}").unwrap();
 		},
 		("Send", _, _) => {}, ("Sync", _, _) => {},
 		("Clone", _, _) => {
@@ -598,13 +653,22 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 			writeln!(w, "\tfn clone(&self) -> Self {{").unwrap();
 			writeln!(w, "\t\t{}_clone(self)", trait_name).unwrap();
 			writeln!(w, "\t}}\n}}").unwrap();
+			writeln!(w, "impl Clone for {}Ref {{", trait_name).unwrap();
+			writeln!(w, "\tfn clone(&self) -> Self {{").unwrap();
+			writeln!(w, "\t\tSelf({}_clone(&self.0))", trait_name).unwrap();
+			writeln!(w, "\t}}\n}}").unwrap();
 		},
 		("std::fmt::Debug", _, _)|("core::fmt::Debug", _, _) => {
 			writeln!(w, "impl core::fmt::Debug for {} {{", trait_name).unwrap();
 			writeln!(w, "\tfn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {{").unwrap();
 			writeln!(w, "\t\tf.write_str((self.debug_str)(self.this_arg).into_str())").unwrap();
 			writeln!(w, "\t}}").unwrap();
 			writeln!(w, "}}").unwrap();
+			writeln!(w, "impl core::fmt::Debug for {}Ref {{", trait_name).unwrap();
+			writeln!(w, "\tfn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {{").unwrap();
+			writeln!(w, "\t\tf.write_str((self.0.debug_str)(self.0.this_arg).into_str())").unwrap();
+			writeln!(w, "\t}}").unwrap();
+			writeln!(w, "}}").unwrap();
 		},
 		(s, i, generic_args) => {
 			if let Some(supertrait) = types.crate_types.traits.get(s) {
@@ -621,9 +685,16 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 						write!(w, " {}", $s).unwrap();
 						maybe_write_generics(w, &$supertrait.generics, $generic_args, types, false);
 						writeln!(w, " for {} {{", trait_name).unwrap();
-
 						impl_trait_for_c!($supertrait, format!(".{}", $i), &resolver, $generic_args);
 						writeln!(w, "}}").unwrap();
+
+						write!(w, "impl").unwrap();
+						maybe_write_lifetime_generics(w, &$supertrait.generics, types);
+						write!(w, " {}", $s).unwrap();
+						maybe_write_generics(w, &$supertrait.generics, $generic_args, types, false);
+						writeln!(w, " for {}Ref {{", trait_name).unwrap();
+						impl_trait_for_c!($supertrait, format!(".0.{}", $i), &resolver, $generic_args);
+						writeln!(w, "}}").unwrap();
 					}
 				}
 				impl_supertrait!(s, supertrait, i, generic_args);
@@ -651,7 +722,7 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
 		impl_trait_for_c!(t, "", types, &syn::PathArguments::None);
 		writeln!(w, "}}\n").unwrap();
 
-		writeln!(w, "struct {}Ref({});", trait_name, trait_name).unwrap();
+		writeln!(w, "pub struct {}Ref({});", trait_name, trait_name).unwrap();
 		write!(w, "impl").unwrap();
 		maybe_write_lifetime_generics(w, &t.generics, types);
 		write!(w, " rust{}", t.ident).unwrap();