+
+// Identity mapping, but only works when the input is syntactically valid. This
+// simulates common proc macros that unnecessarily parse their input and return
+// compile errors.
+#[derive(Debug)]
+struct IdentityWhenValidProcMacroExpander;
+impl base_db::ProcMacroExpander for IdentityWhenValidProcMacroExpander {
+ fn expand(
+ &self,
+ subtree: &Subtree,
+ _: Option<&Subtree>,
+ _: &base_db::Env,
+ ) -> Result<Subtree, base_db::ProcMacroExpansionError> {
+ let (parse, _) =
+ ::mbe::token_tree_to_syntax_node(subtree, ::mbe::TopEntryPoint::MacroItems);
+ if parse.errors().is_empty() {
+ Ok(subtree.clone())
+ } else {
+ panic!("got invalid macro input: {:?}", parse.errors());
+ }
+ }
+}