crashes: add another test showing that everything works fine when we need compile-flags to repro an ice and add README

Author: matthiaskrgr

src/tools/opt-dist/src/tests.rs

@@ -96,7 +96,7 @@ llvm-config = "{llvm_config}"
         "tests/pretty",
         "tests/run-pass-valgrind",
         "tests/ui",
-        "tests/crases",
+        "tests/crashes",
     ];
     for test_path in env.skipped_tests() {
         args.extend(["--skip", test_path]);

tests/crashes/122909.rs

@@ -0,0 +1,15 @@
+//@ compile-flags: -Zpolymorphize=on -Zinline-mir=yes
+//@ known-bug: #12345
+
+
+use std::sync::{Arc, Context, Weak};
+
+pub struct WeakOnce<T>();
+impl<T> WeakOnce<T> {
+    extern "rust-call" fn try_get(&self) -> Option<Arc<T>> {}
+
+    pub fn get(&self) -> Arc<T> {
+        self.try_get()
+            .unwrap_or_else(|| panic!("Singleton {} not available", std::any::type_name::<T>()))
+    }
+}

tests/crashes/README.md

@@ -0,0 +1,13 @@
+This is serves as a collection of crashes so that accidental ICE fixes are tracked.
+This was formally done at https://github.com/rust-lang/glacier but doing it inside
+the rustc testsuite is more convenient.
+
+It is imperative that a test in the suite causes an internal compiler error/panic
+or makes rustc crash in some other way.
+Accepted exit codes are: 101 (may be expanded later)
+
+When adding crashes from https://github.com/rust-lang/rust/issues, the
+issue number should be noted in the file name (12345.rs should suffice)
+and perhaps also inside the file via `//@ known-bug #4321`
+
+If you happen to fix one of the crashes, please move it to `tests/ui`! :)