codegen: ignore aliases for decltypes we can't resolve.

We do the same for template parameters with `typename` on aliases.

This is not great, but it's better than generating invalid code.

Author: emilio

libbindgen/src/codegen/mod.rs

@@ -515,6 +515,30 @@ impl CodeGenerator for Type {
                     inner_item.to_rust_ty(ctx)
                 };
 
+                {
+                    // FIXME(emilio): This is a workaround to avoid generating
+                    // incorrect type aliases because of types that we haven't
+                    // been able to resolve (because, eg, they depend on a
+                    // template parameter).
+                    //
+                    // It's kind of a shame not generating them even when they
+                    // could be referenced, but we already do the same for items
+                    // with invalid template parameters, and at least this way
+                    // they can be replaced, instead of generating plain invalid
+                    // code.
+                    let inner_canon_type =
+                        inner_item.expect_type().canonical_type(ctx);
+                    if inner_canon_type.is_named() &&
+                        inner_canon_type.name().map_or(false, |name| {
+                            name.contains("decltype ") ||
+                            name.contains("decltype(")
+                        }) {
+                        warn!("Item contained `decltype`d type, skipping: \
+                              {:?}, {:?}", item, inner_item);
+                        return;
+                    }
+                }
+
                 let rust_name = ctx.rust_ident(&name);
                 let mut typedef = aster::AstBuilder::new().item().pub_();
 

libbindgen/tests/expectations/tests/381-decltype-alias.rs

@@ -0,0 +1,12 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(non_snake_case)]
+
+
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct std_allocator_traits<_Alloc> {
+    pub _address: u8,
+    pub _phantom_0: ::std::marker::PhantomData<_Alloc>,
+}

libbindgen/tests/headers/381-decltype-alias.hpp

@@ -0,0 +1,7 @@
+// bindgen-flags: -- -std=c++11
+
+namespace std {
+  template<typename _Alloc> struct allocator_traits {
+    typedef decltype ( _S_size_type_helper ( ( _Alloc * ) 0 ) ) __size_type;
+  };
+}