Auto merge of #1241 - RalfJung:dont-panic, r=RalfJung

whitelist platforms where panicking should work

@CAD97 [proposed](#1059 (comment)) trying to get a better error for failed panics on Windows.

Could you test if this works for you?

Author: bors

src/shims/foreign_items.rs

@@ -132,6 +132,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 // This matches calls to the foreign item `panic_impl`.
                 // The implementation is provided by the function with the `#[panic_handler]` attribute.
                 "panic_impl" => {
+                    // Make sure panicking actually works on this platform.
+                    match this.tcx.sess.target.target.target_os.as_str() {
+                        "linux" | "macos" => {},
+                        _ => throw_unsup_format!("panicking is not supported on this platform"),
+                    }
+
                     let panic_impl_id = this.tcx.lang_items().panic_impl().unwrap();
                     let panic_impl_instance = ty::Instance::mono(*this.tcx, panic_impl_id);
                     return Ok(Some(&*this.load_mir(panic_impl_instance.def, None)?));

tests/compile-fail/panic/windows.rs

@@ -0,0 +1,9 @@
+// ignore-linux
+// ignore-macos
+
+// Test that panics on Windows give a reasonable error message.
+
+// error-pattern: panicking is not supported on this platform
+fn main() {
+    panic!("this is Windows");
+}