typecheck: Special case builtin types when typechecking types.

Type definition conflicts are allowed in the case of builtin types. This is used in the
`core` crate to add some more functionality to the builtin types. The consequence of this
is that we need to special case the resolution of types in the case that their name could
refer to a module or to a builtin type.

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::resolve_root_path): Add
	special casing for resolving to the builtin type definition if the found type
	has the same name and is a module.

gcc/testsuite/ChangeLog:

	* rust/compile/type-with-builtin-type-name.rs: New test.

Author: CohenArthur

gcc/rust/typecheck/rust-hir-type-check-type.cc

@@ -31,6 +31,7 @@
 #include "rust-type-util.h"
 #include "rust-system.h"
 #include "rust-compile-base.h"
+#include "rust-resolve-builtins.h"
 
 namespace Rust {
 namespace Resolver {
@@ -349,6 +350,14 @@ TypeCheckType::resolve_root_path (HIR::TypePath &path, size_t *offset,
 	  // assign the ref_node_id if we've found something
 	  nr_ctx.lookup (ast_node_id, Resolver2_0::Namespace::Types)
 	    .map ([&ref_node_id] (NodeId resolved) { ref_node_id = resolved; });
+
+	  // TODO: Should we add a special method to the name resolver to handle
+	  // that case? Resolving something in the Types NS when we want to
+	  // prioritize builtin types over modules or other conflicting things?
+	  if (auto builtin_type_id
+	      = Resolver2_0::Builtins::find_builtin_node_id (seg->to_string ()))
+	    if (mappings.is_module (ref_node_id))
+	      ref_node_id = builtin_type_id.value ();
 	}
 
       // ref_node_id is the NodeId that the segments refers to.
@@ -411,7 +420,8 @@ TypeCheckType::resolve_root_path (HIR::TypePath &path, size_t *offset,
 	  // A::B::C::this_is_a_module
 	  //          ^^^^^^^^^^^^^^^^
 	  // This is an error, we are not expecting a module.
-	  rust_error_at (seg->get_locus (), "expected value");
+	  rust_error_at (seg->get_locus (), "expected value, got module");
+
 	  return new TyTy::ErrorType (path.get_mappings ().get_hirid ());
 	}
 

gcc/testsuite/rust/compile/type-with-builtin-type-name.rs

@@ -0,0 +1,8 @@
+#![feature(no_core)]
+#![no_core]
+
+struct i32;
+
+fn main() {
+    let _: i32 = i32;
+}