Fix panic on eager expansion

crates/ra_hir_expand/src/eager.rs

@@ -37,9 +37,25 @@ pub fn expand_eager_macro(
 ) -> Option<EagerMacroId> {
     let args = macro_call.value.token_tree()?;
     let parsed_args = mbe::ast_to_token_tree(&args)?.0;
-    let parsed_args = mbe::token_tree_to_syntax_node(&parsed_args, FragmentKind::Expr).ok()?.0;
-    let result = eager_macro_recur(db, macro_call.with_value(parsed_args.syntax_node()), resolver)?;
 
+    // Note:
+    // When `lazy_expand` is called, its *parent* file must be already exists.
+    // Here we store an eager macro id for the argument expaned here
+    // for that purpose.
+    let arg_id: MacroCallId = db
+        .intern_eager_expansion({
+            EagerCallLoc {
+                def,
+                fragment: FragmentKind::Expr,
+                subtree: Arc::new(parsed_args.clone()),
+                file_id: macro_call.file_id,
+            }
+        })
+        .into();
+
+    let parsed_args = mbe::token_tree_to_syntax_node(&parsed_args, FragmentKind::Expr).ok()?.0;
+    let result =
+        eager_macro_recur(db, InFile::new(arg_id.as_file(), parsed_args.syntax_node()), resolver)?;
     let subtree = to_subtree(&result)?;
 
     if let MacroDefKind::BuiltInEager(eager) = def.kind {

crates/ra_hir_ty/src/tests/macros.rs

@@ -438,6 +438,27 @@ fn main() {
     );
 }
 
+#[test]
+fn infer_builtin_macros_concat_with_lazy() {
+    assert_snapshot!(
+        infer(r#"
+macro_rules! hello {() => {"hello"}}
+
+#[rustc_builtin_macro]
+macro_rules! concat {() => {}}
+
+fn main() {
+    let x = concat!(hello!(), concat!("world", "!"));
+}
+"#),
+        @r###"
+    ![0; 13) '"helloworld!"': &str
+    [104; 161) '{     ...")); }': ()
+    [114; 115) 'x': &str
+    "###
+    );
+}
+
 #[test]
 fn infer_derive_clone_simple() {
     let (db, pos) = TestDB::with_position(