From a8c152dfc921e8ec2c00f65e7c731197e522a96d Mon Sep 17 00:00:00 2001
From: Bastian Kauschke <bastian_kauschke@hotmail.de>
Date: Sat, 9 May 2020 22:01:15 +0200
Subject: [PATCH] add regression tests + improve method name

---
 .../traits/fulfill.rs                         |  8 ++---
 .../issue-70180-1-stalled_on.rs               | 35 +++++++++++++++++++
 .../issue-70180-2-stalled_on.rs               | 35 +++++++++++++++++++
 3 files changed, 74 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/const-generics/issue-70180-1-stalled_on.rs
 create mode 100644 src/test/ui/const-generics/issue-70180-2-stalled_on.rs

diff --git a/src/librustc_trait_selection/traits/fulfill.rs b/src/librustc_trait_selection/traits/fulfill.rs
index 1e056c96acd38..dfffdbedf4ca4 100644
--- a/src/librustc_trait_selection/traits/fulfill.rs
+++ b/src/librustc_trait_selection/traits/fulfill.rs
@@ -355,7 +355,7 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
                         // trait selection is because we don't have enough
                         // information about the types in the trait.
                         pending_obligation.stalled_on =
-                            trait_ref_type_vars(self.selcx, data.to_poly_trait_ref());
+                            trait_ref_infer_vars(self.selcx, data.to_poly_trait_ref());
 
                         debug!(
                             "process_predicate: pending obligation {:?} now stalled on {:?}",
@@ -433,7 +433,7 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
                     Ok(None) => {
                         let tcx = self.selcx.tcx();
                         pending_obligation.stalled_on =
-                            trait_ref_type_vars(self.selcx, data.to_poly_trait_ref(tcx));
+                            trait_ref_infer_vars(self.selcx, data.to_poly_trait_ref(tcx));
                         ProcessResult::Unchanged
                     }
                     Ok(Some(os)) => ProcessResult::Changed(mk_pending(infcx, os)),
@@ -539,8 +539,8 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
     }
 }
 
-/// Returns the set of type inference variables contained in a trait ref.
-fn trait_ref_type_vars<'a, 'tcx>(
+/// Returns the set of inference variables contained in a trait ref.
+fn trait_ref_infer_vars<'a, 'tcx>(
     selcx: &mut SelectionContext<'a, 'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>,
 ) -> Vec<TyOrConstInferVar<'tcx>> {
diff --git a/src/test/ui/const-generics/issue-70180-1-stalled_on.rs b/src/test/ui/const-generics/issue-70180-1-stalled_on.rs
new file mode 100644
index 0000000000000..ff2a5250263d5
--- /dev/null
+++ b/src/test/ui/const-generics/issue-70180-1-stalled_on.rs
@@ -0,0 +1,35 @@
+// build-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+pub fn works() {
+    let array/*: [_; _]*/ = default_array();
+    let _: [_; 4] = array;
+    Foo::foo(&array);
+}
+
+pub fn didnt_work() {
+    let array/*: [_; _]*/ = default_array();
+    Foo::foo(&array);
+    let _: [_; 4] = array;
+}
+
+trait Foo {
+    fn foo(&self) {}
+}
+
+impl Foo for [i32; 4] {}
+impl Foo for [i64; 8] {}
+
+// Only needed because `[_; _]` is not valid type syntax.
+fn default_array<T, const N: usize>() -> [T; N]
+where
+    [T; N]: Default,
+{
+    Default::default()
+}
+
+fn main() {
+    works();
+    didnt_work();
+}
diff --git a/src/test/ui/const-generics/issue-70180-2-stalled_on.rs b/src/test/ui/const-generics/issue-70180-2-stalled_on.rs
new file mode 100644
index 0000000000000..83338668f4ffd
--- /dev/null
+++ b/src/test/ui/const-generics/issue-70180-2-stalled_on.rs
@@ -0,0 +1,35 @@
+// build-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+fn works() {
+    let array/*: [u8; _]*/ = default_byte_array();
+    let _: [_; 4] = array;
+    Foo::foo(&array);
+}
+
+fn didnt_work() {
+    let array/*: [u8; _]*/ = default_byte_array();
+    Foo::foo(&array);
+    let _: [_; 4] = array;
+}
+
+trait Foo<T> {
+    fn foo(&self) {}
+}
+
+impl Foo<i32> for [u8; 4] {}
+impl Foo<i64> for [u8; 8] {}
+
+// Only needed because `[u8; _]` is not valid type syntax.
+fn default_byte_array<const N: usize>() -> [u8; N]
+where
+    [u8; N]: Default,
+{
+    Default::default()
+}
+
+fn main() {
+    works();
+    didnt_work();
+}