From 50e34d6d658c4906a3292385b1962a3c26ce24c4 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <huyuumi.dev@gmail.com>
Date: Fri, 23 Oct 2020 18:00:18 +0900
Subject: [PATCH] Do not try to report on closures to avoid ICE

---
 .../nice_region_error/static_impl_trait.rs     |  8 ++++++++
 src/test/ui/regions/issue-78262.rs             |  9 +++++++++
 src/test/ui/regions/issue-78262.stderr         | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 src/test/ui/regions/issue-78262.rs
 create mode 100644 src/test/ui/regions/issue-78262.stderr

diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
index 441cfeea20a48..e9d5ebad7de03 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -39,6 +39,14 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             ) if **sub_r == RegionKind::ReStatic => {
                 // This is for an implicit `'static` requirement coming from `impl dyn Trait {}`.
                 if let ObligationCauseCode::UnifyReceiver(ctxt) = &cause.code {
+                    // This may have a closure and it would cause ICE
+                    // through `find_param_with_region` (#78262).
+                    let anon_reg_sup = tcx.is_suitable_region(sup_r)?;
+                    let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);
+                    if fn_returns.is_empty() {
+                        return None;
+                    }
+
                     let param = self.find_param_with_region(sup_r, sub_r)?;
                     let lifetime = if sup_r.has_name() {
                         format!("lifetime `{}`", sup_r)
diff --git a/src/test/ui/regions/issue-78262.rs b/src/test/ui/regions/issue-78262.rs
new file mode 100644
index 0000000000000..2324152d2c081
--- /dev/null
+++ b/src/test/ui/regions/issue-78262.rs
@@ -0,0 +1,9 @@
+trait TT {}
+
+impl dyn TT {
+    fn func(&self) {}
+}
+
+fn main() {
+    let f = |x: &dyn TT| x.func(); //~ ERROR: mismatched types
+}
diff --git a/src/test/ui/regions/issue-78262.stderr b/src/test/ui/regions/issue-78262.stderr
new file mode 100644
index 0000000000000..580cea00ecd4f
--- /dev/null
+++ b/src/test/ui/regions/issue-78262.stderr
@@ -0,0 +1,18 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-78262.rs:8:28
+   |
+LL |     let f = |x: &dyn TT| x.func();
+   |                            ^^^^ lifetime mismatch
+   |
+   = note: expected reference `&(dyn TT + 'static)`
+              found reference `&dyn TT`
+note: the anonymous lifetime #1 defined on the body at 8:13...
+  --> $DIR/issue-78262.rs:8:13
+   |
+LL |     let f = |x: &dyn TT| x.func();
+   |             ^^^^^^^^^^^^^^^^^^^^^
+   = note: ...does not necessarily outlive the static lifetime
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.