// check-pass

// This test exhibits undefined behavior, but it is impossible to prevent generally during
// const eval, even if it could be prevented in the cases here if we added expensive and
// complex checks in rustc.
// The reason it's impossible in general
// is that we run into query cycles even *without* UB, just because we're checking for UB.
// We do not detect it if you create references to statics
// in ways that are UB.

enum Foo {
    A = 5,
    B = 42,
}
enum Bar {
    C = 42,
    D = 99,
}
#[repr(C)]
union Union {
    foo: &'static Foo,
    bar: &'static Bar,
    u8: &'static u8,
}
static BAR: u8 = 5;
static FOO: (&Foo, &Bar) = unsafe {
    (
        // undefined behavior
        Union { u8: &BAR }.foo,
        Union { u8: &BAR }.bar,
    )
};
static FOO2: (&Foo, &Bar) = unsafe { (std::mem::transmute(&BAR), std::mem::transmute(&BAR)) };
//^ undefined behavior

fn main() {}

// check-pass

// This test exhibits undefined behavior, but it is impossible to prevent generally during
// const eval, even if possible to prevent in the cases here. The reason it's impossible in general
// is that we run into query cycles even *without* UB, just because we're checking for UB.
// We do not detect it if you create references to statics
// in ways that are UB.

enum Foo {
    A = 5,
    B = 42,
}
enum Bar {
    C = 42,
    D = 99,
}
#[repr(C)]
union Union {
    foo: &'static Foo,
    bar: &'static Bar,
    u8: &'static u8,
}
static BAR: u8 = 5;
static FOO: (&Foo, &Bar) = unsafe {
    (
        // undefined behavior
        Union { u8: &BAR }.foo,
        Union { u8: &BAR }.bar,
    )
};
static FOO2: (&Foo, &Bar) = unsafe { (std::mem::transmute(&BAR), std::mem::transmute(&BAR)) };
//^ undefined behavior

fn main() {}

--- 
+++ 
@@ -1,7 +1,9 @@
 // check-pass
 
 // This test exhibits undefined behavior, but it is impossible to prevent generally during
-// const eval, even if possible to prevent in the cases here. The reason it's impossible in general
+// const eval, even if it could be prevented in the cases here if we added expensive and
+// complex checks in rustc.
+// The reason it's impossible in general
 // is that we run into query cycles even *without* UB, just because we're checking for UB.
 // We do not detect it if you create references to statics
 // in ways that are UB.
Clarify a statement in UB test
