check if a static is extern before trying to promote

Author: sjwang05

compiler/rustc_mir_transform/src/promote_consts.rs

@@ -317,6 +317,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                     // can only promote static accesses inside statics.
                     && let Some(hir::ConstContext::Static(..)) = self.const_kind
                     && !self.tcx.is_thread_local_static(did)
+                    && !self.tcx.is_foreign_item(did)
                 {
                     // Recurse.
                 } else {

tests/ui/statics/extern-static-in-static-ice-143174.rs

@@ -0,0 +1,15 @@
+// Regression test for #143174.
+
+#![crate_type = "lib"]
+
+type Fun = unsafe extern "C" fn();
+
+struct Foo(Fun);
+
+static FOO: &Foo = &Foo(BAR);
+//~^ ERROR cannot access extern static `BAR` [E0080]
+//~| ERROR use of extern static is unsafe and requires unsafe function or block [E0133]
+
+unsafe extern "C" {
+    static BAR: Fun;
+}

tests/ui/statics/extern-static-in-static-ice-143174.stderr

@@ -0,0 +1,18 @@
+error[E0080]: cannot access extern static `BAR`
+  --> $DIR/extern-static-in-static-ice-143174.rs:9:25
+   |
+LL | static FOO: &Foo = &Foo(BAR);
+   |                         ^^^ evaluation of `FOO` failed here
+
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
+  --> $DIR/extern-static-in-static-ice-143174.rs:9:25
+   |
+LL | static FOO: &Foo = &Foo(BAR);
+   |                         ^^^ use of extern static
+   |
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0080, E0133.
+For more information about an error, try `rustc --explain E0080`.