From c0d29fe7d7a32dbadad161fe8a39bc996da3c633 Mon Sep 17 00:00:00 2001
From: varkor <github@varkor.com>
Date: Sun, 18 Oct 2020 22:40:50 +0100
Subject: [PATCH] Fix issue with specifying generic arguments for primitive
 types

---
 compiler/rustc_typeck/src/collect/type_of.rs     | 16 ++++++++++------
 src/test/ui/usize-generic-argument-parent.rs     |  5 +++++
 src/test/ui/usize-generic-argument-parent.stderr |  9 +++++++++
 3 files changed, 24 insertions(+), 6 deletions(-)
 create mode 100644 src/test/ui/usize-generic-argument-parent.rs
 create mode 100644 src/test/ui/usize-generic-argument-parent.stderr

diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs
index 4b3250a1d44..5fb6eaf69df 100644
--- a/compiler/rustc_typeck/src/collect/type_of.rs
+++ b/compiler/rustc_typeck/src/collect/type_of.rs
@@ -112,12 +112,16 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                         tcx.sess.delay_span_bug(tcx.def_span(def_id), "anon const with Res::Err");
                         return None;
                     }
-                    _ => span_bug!(
-                        DUMMY_SP,
-                        "unexpected anon const res {:?} in path: {:?}",
-                        res,
-                        path,
-                    ),
+                    _ => {
+                        // If the user tries to specify generics on a type that does not take them,
+                        // e.g. `usize<T>`, we may hit this branch, in which case we treat it as if
+                        // no arguments have been passed. An error should already have been emitted.
+                        tcx.sess.delay_span_bug(
+                            tcx.def_span(def_id),
+                            &format!("unexpected anon const res {:?} in path: {:?}", res, path),
+                        );
+                        return None;
+                    }
                 };
 
                 generics
diff --git a/src/test/ui/usize-generic-argument-parent.rs b/src/test/ui/usize-generic-argument-parent.rs
new file mode 100644
index 00000000000..46b06e2b366
--- /dev/null
+++ b/src/test/ui/usize-generic-argument-parent.rs
@@ -0,0 +1,5 @@
+fn foo() {
+    let x: usize<foo>; //~ ERROR const arguments are not allowed for this type
+}
+
+fn main() {}
diff --git a/src/test/ui/usize-generic-argument-parent.stderr b/src/test/ui/usize-generic-argument-parent.stderr
new file mode 100644
index 00000000000..f1eae3b5008
--- /dev/null
+++ b/src/test/ui/usize-generic-argument-parent.stderr
@@ -0,0 +1,9 @@
+error[E0109]: const arguments are not allowed for this type
+  --> $DIR/usize-generic-argument-parent.rs:2:18
+   |
+LL |     let x: usize<foo>;
+   |                  ^^^ const argument not allowed
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0109`.