3 files changed, 72 insertions, 3 deletions

diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index b7e8855fb..7f5e1469e 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -516,9 +516,31 @@ pub(crate) fn inherent_impl_substs(
     let self_ty_with_vars =
         Canonical { num_vars: vars.len() + self_ty.num_vars, value: self_ty_with_vars };
     let substs = super::infer::unify(&self_ty_with_vars, self_ty);
-    // we only want the substs for the vars we added, not the ones from self_ty
-    let result = substs.map(|s| s.suffix(vars.len()));
-    result
+    // We only want the substs for the vars we added, not the ones from self_ty.
+    // Also, if any of the vars we added are still in there, we replace them by
+    // Unknown. I think this can only really happen if self_ty contained
+    // Unknown, and in that case we want the result to contain Unknown in those
+    // places again.
+    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.num_vars))
+}
+
+/// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
+/// num_vars_to_keep) by `Ty::Unknown`.
+fn fallback_bound_vars(s: Substs, num_vars_to_keep: usize) -> Substs {
+    s.fold_binders(
+        &mut |ty, binders| {
+            if let Ty::Bound(idx) = &ty {
+                if *idx >= binders as u32 {
+                    Ty::Unknown
+                } else {
+                    ty
+                }
+            } else {
+                ty
+            }
+        },
+        num_vars_to_keep,
+    )
 }
 
 fn transform_receiver_ty(
diff --git a/crates/ra_hir_ty/src/test_db.rs b/crates/ra_hir_ty/src/test_db.rs
index c794f7b84..0be2fea4b 100644
--- a/crates/ra_hir_ty/src/test_db.rs
+++ b/crates/ra_hir_ty/src/test_db.rs
@@ -67,6 +67,13 @@ impl FileLoader for TestDB {
     fn relevant_crates(&self, file_id: FileId) -> Arc<Vec<CrateId>> {
         FileLoaderDelegate(self).relevant_crates(file_id)
     }
+    fn resolve_extern_path(
+        &self,
+        extern_id: ra_db::ExternSourceId,
+        relative_path: &RelativePath,
+    ) -> Option<FileId> {
+        FileLoaderDelegate(self).resolve_extern_path(extern_id, relative_path)
+    }
 }
 
 impl TestDB {
diff --git a/crates/ra_hir_ty/src/tests/macros.rs b/crates/ra_hir_ty/src/tests/macros.rs
index ffa78b046..3b7022ad5 100644
--- a/crates/ra_hir_ty/src/tests/macros.rs
+++ b/crates/ra_hir_ty/src/tests/macros.rs
@@ -363,6 +363,26 @@ fn main() {
 }
 
 #[test]
+fn infer_local_macro() {
+    assert_snapshot!(
+        infer(r#"
+fn main() {
+    macro_rules! foo {
+        () => { 1usize }
+    }
+    let _a  = foo!();
+}
+"#),
+        @r###"
+        ![0; 6) '1usize': usize
+        [11; 90) '{     ...!(); }': ()
+        [17; 66) 'macro_...     }': {unknown}
+        [75; 77) '_a': usize
+    "###
+    );
+}
+
+#[test]
 fn infer_builtin_macros_line() {
     assert_snapshot!(
         infer(r#"
@@ -550,6 +570,26 @@ fn main() {
 }
 
 #[test]
+fn infer_builtin_macros_env() {
+    assert_snapshot!(
+        infer(r#"
+//- /main.rs env:foo=bar
+#[rustc_builtin_macro]
+macro_rules! env {() => {}}
+
+fn main() {
+    let x = env!("foo");
+}
+"#),
+        @r###"
+    ![0; 5) '"bar"': &str
+    [88; 116) '{     ...o"); }': ()
+    [98; 99) 'x': &str
+    "###
+    );
+}
+
+#[test]
 fn infer_derive_clone_simple() {
     let (db, pos) = TestDB::with_position(
         r#"