Resolve through type refs and aliases when marking type params used

In stylo bindings generation, we were hitting bugs where the analysis saw a
template type parameter behind a type ref to a type alias, and this was then
used as an argument to a template instantiation. Because of the indirection, the
analysis got confused and ignored the template argument because it was "not" a
named template type, and therefore we didn't care about its usage.

This commit makes sure that we keep resolving through type references and
aliases to find the inner named template type parameter to add to the current
item's usage set.

Fixes #638.

3 files changed, 39 insertions, 0 deletions

diff --git a/src/ir/named.rs b/src/ir/named.rs
index 39fa2201..17f46eca 100644
--- a/src/ir/named.rs
+++ b/src/ir/named.rs
@@ -481,6 +481,10 @@ impl<'ctx, 'gen> MonotoneFramework for UsedTemplateParameters<'ctx, 'gen> {
                     if used_by_def.contains(param) {
                         debug!("        param is used by template definition");
 
+                        let arg = arg.into_resolver()
+                            .through_type_refs()
+                            .through_type_aliases()
+                            .resolve(self.ctx);
                         if let Some(named) = arg.as_named(self.ctx, &()) {
                             debug!("        arg is a type parameter, marking used");
                             used_by_this_id.insert(named);
diff --git a/tests/expectations/tests/issue-638-stylo-cannot-find-T-in-this-scope.rs b/tests/expectations/tests/issue-638-stylo-cannot-find-T-in-this-scope.rs
new file mode 100644
index 00000000..4ff0b5bc
--- /dev/null
+++ b/tests/expectations/tests/issue-638-stylo-cannot-find-T-in-this-scope.rs
@@ -0,0 +1,23 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(non_snake_case)]
+
+
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct RefPtr<T> {
+    pub use_of_t: T,
+}
+impl <T> Default for RefPtr<T> {
+    fn default() -> Self { unsafe { ::std::mem::zeroed() } }
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct UsesRefPtrWithAliasedTypeParam<U> {
+    pub member: RefPtr<UsesRefPtrWithAliasedTypeParam_V<U>>,
+}
+pub type UsesRefPtrWithAliasedTypeParam_V<U> = U;
+impl <U> Default for UsesRefPtrWithAliasedTypeParam<U> {
+    fn default() -> Self { unsafe { ::std::mem::zeroed() } }
+}
diff --git a/tests/headers/issue-638-stylo-cannot-find-T-in-this-scope.hpp b/tests/headers/issue-638-stylo-cannot-find-T-in-this-scope.hpp
new file mode 100644
index 00000000..13b656e1
--- /dev/null
+++ b/tests/headers/issue-638-stylo-cannot-find-T-in-this-scope.hpp
@@ -0,0 +1,12 @@
+// bindgen-flags: -- -std=c++14
+
+template <class T>
+class RefPtr {
+    T use_of_t;
+};
+
+template <typename U>
+class UsesRefPtrWithAliasedTypeParam {
+    using V = U;
+    RefPtr<V> member;
+};