From 6ed16e23b1bd6a294508e2597914977b767c568c Mon Sep 17 00:00:00 2001
From: Fabian Wolff <fabian.wolff@alumni.ethz.ch>
Date: Sat, 12 Jun 2021 18:32:25 +0200
Subject: [PATCH 1/2] Report an error if resolution of closure call functions
 failed

---
 compiler/rustc_typeck/src/check/callee.rs | 11 +++++++++--
 src/test/ui/lang-items/issue-86238.rs     | 16 ++++++++++++++++
 src/test/ui/lang-items/issue-86238.stderr | 10 ++++++++++
 3 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/lang-items/issue-86238.rs
 create mode 100644 src/test/ui/lang-items/issue-86238.stderr

diff --git a/compiler/rustc_typeck/src/check/callee.rs b/compiler/rustc_typeck/src/check/callee.rs
index cb8f336721ad6..9362daa3c889e 100644
--- a/compiler/rustc_typeck/src/check/callee.rs
+++ b/compiler/rustc_typeck/src/check/callee.rs
@@ -588,10 +588,17 @@ impl<'a, 'tcx> DeferredCallResolution<'tcx> {
                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
             }
             None => {
-                span_bug!(
+                // This can happen if `#![no_core]` is used and the `fn/fn_mut/fn_once`
+                // lang items are not defined (issue #86238).
+                let mut err = fcx.inh.tcx.sess.struct_span_err(
                     self.call_expr.span,
-                    "failed to find an overloaded call trait for closure call"
+                    "failed to find an overloaded call trait for closure call",
                 );
+                err.help(
+                    "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
+                     and have an associated `call`/`call_mut`/`call_once` function",
+                );
+                err.emit();
             }
         }
     }
diff --git a/src/test/ui/lang-items/issue-86238.rs b/src/test/ui/lang-items/issue-86238.rs
new file mode 100644
index 0000000000000..509f94f3834a5
--- /dev/null
+++ b/src/test/ui/lang-items/issue-86238.rs
@@ -0,0 +1,16 @@
+// Regression test for the ICE described in issue #86238.
+
+#![feature(lang_items)]
+#![feature(no_core)]
+
+#![no_core]
+fn main() {
+    let one = || {};
+    one()
+    //~^ ERROR: failed to find an overloaded call trait for closure call
+    //~| HELP: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined
+}
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
diff --git a/src/test/ui/lang-items/issue-86238.stderr b/src/test/ui/lang-items/issue-86238.stderr
new file mode 100644
index 0000000000000..070f2762634bb
--- /dev/null
+++ b/src/test/ui/lang-items/issue-86238.stderr
@@ -0,0 +1,10 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/issue-86238.rs:9:5
+   |
+LL |     one()
+   |     ^^^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have an associated `call`/`call_mut`/`call_once` function
+
+error: aborting due to previous error
+

From dab25ab56cd7a8132281621ecdf7aee8dfdabd15 Mon Sep 17 00:00:00 2001
From: Fabian Wolff <fabian.wolff@alumni.ethz.ch>
Date: Thu, 1 Jul 2021 13:26:17 +0200
Subject: [PATCH 2/2] Reword error message slightly

---
 compiler/rustc_typeck/src/check/callee.rs | 2 +-
 src/test/ui/lang-items/issue-86238.stderr | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_typeck/src/check/callee.rs b/compiler/rustc_typeck/src/check/callee.rs
index 9362daa3c889e..f55093d82f883 100644
--- a/compiler/rustc_typeck/src/check/callee.rs
+++ b/compiler/rustc_typeck/src/check/callee.rs
@@ -596,7 +596,7 @@ impl<'a, 'tcx> DeferredCallResolution<'tcx> {
                 );
                 err.help(
                     "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
-                     and have an associated `call`/`call_mut`/`call_once` function",
+                     and have associated `call`/`call_mut`/`call_once` functions",
                 );
                 err.emit();
             }
diff --git a/src/test/ui/lang-items/issue-86238.stderr b/src/test/ui/lang-items/issue-86238.stderr
index 070f2762634bb..767e6de2263b9 100644
--- a/src/test/ui/lang-items/issue-86238.stderr
+++ b/src/test/ui/lang-items/issue-86238.stderr
@@ -4,7 +4,7 @@ error: failed to find an overloaded call trait for closure call
 LL |     one()
    |     ^^^^^
    |
-   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have an associated `call`/`call_mut`/`call_once` function
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have associated `call`/`call_mut`/`call_once` functions
 
 error: aborting due to previous error