Fix crash for super trait cycles

Cargo.lock

@@ -1007,7 +1007,6 @@ dependencies = [
  "chalk-solve 0.1.0 (git+https://github.com/rust-lang/chalk.git)",
  "ena 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "insta 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lalrpop-intern 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "once_cell 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",

crates/ra_hir/Cargo.toml

@@ -12,7 +12,6 @@ rustc-hash = "1.0"
 parking_lot = "0.9.0"
 ena = "0.13"
 once_cell = "1.0.1"
-itertools = "0.8.0"
 
 ra_syntax = { path = "../ra_syntax" }
 ra_arena = { path = "../ra_arena" }

crates/ra_hir/src/code_model.rs

@@ -1,11 +1,8 @@
 pub(crate) mod src;
 pub(crate) mod docs;
 
-use std::iter;
 use std::sync::Arc;
 
-use itertools::Itertools;
-
 use ra_db::{CrateId, Edition, FileId, SourceRootId};
 use ra_syntax::ast::{self, NameOwner, TypeAscriptionOwner};
 
@@ -849,20 +846,23 @@ impl Trait {
 
     /// Returns an iterator over the whole super trait hierarchy (including the
     /// trait itself).
-    pub fn all_super_traits<'a>(
+    pub fn all_super_traits(self, db: &impl HirDatabase) -> Vec<Trait> {
-        self,
+        // we need to take care a bit here to avoid infinite loops in case of cycles
-        db: &'a impl HirDatabase,
+        // (i.e. if we have `trait A: B; trait B: A;`)
-    ) -> impl Iterator<Item = Trait> + 'a {
+        let mut result = vec![self];
-        self.all_super_traits_inner(db).unique()
+        let mut i = 0;
-    }
+        while i < result.len() {
-
+            let t = result[i];
-    fn all_super_traits_inner<'a>(
+            // yeah this is quadratic, but trait hierarchies should be flat
-        self,
+            // enough that this doesn't matter
-        db: &'a impl HirDatabase,
+            for tt in t.direct_super_traits(db) {
-    ) -> impl Iterator<Item = Trait> + 'a {
+                if !result.contains(&tt) {
-        iter::once(self).chain(self.direct_super_traits(db).into_iter().flat_map(move |t| {
+                    result.push(tt);
-            iter::once(t).chain(Box::new(t.all_super_traits(db)) as Box<dyn Iterator<Item = Trait>>)
+                }
-        }))
+            }
+            i += 1;
+        }
+        result
     }
 
     pub fn associated_type_by_name(self, db: &impl DefDatabase, name: &Name) -> Option<TypeAlias> {
@@ -882,7 +882,7 @@ impl Trait {
         db: &impl HirDatabase,
         name: &Name,
     ) -> Option<TypeAlias> {
-        self.all_super_traits(db).find_map(|t| t.associated_type_by_name(db, name))
+        self.all_super_traits(db).into_iter().find_map(|t| t.associated_type_by_name(db, name))
     }
 
     pub(crate) fn trait_data(self, db: &impl DefDatabase) -> Arc<TraitData> {

crates/ra_hir/src/ty/tests.rs

@@ -3694,6 +3694,27 @@ fn test<T: Trait1, U: Trait2>(x: T, y: U) {
     );
 }
 
+#[test]
+fn super_trait_cycle() {
+    // This just needs to not crash
+    assert_snapshot!(
+        infer(r#"
+trait A: B {}
+trait B: A {}
+
+fn test<T: A>(x: T) {
+    x.foo();
+}
+"#),
+        @r###"
+    [44; 45) 'x': T
+    [50; 66) '{     ...o(); }': ()
+    [56; 57) 'x': T
+    [56; 63) 'x.foo()': {unknown}
+    "###
+    );
+}
+
 #[test]
 fn super_trait_assoc_type_bounds() {
     assert_snapshot!(