diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs index bcad7855c3736..43b2f0e91102d 100644 --- a/src/librustc_mir/interpret/memory.rs +++ b/src/librustc_mir/interpret/memory.rs @@ -400,7 +400,16 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> { // We can still be zero-sized in this branch, in which case we have to // return `None`. - if size.bytes() == 0 { None } else { Some(ptr) } + if size.bytes() == 0 { + // We may be reading from a static. + // In order to ensure that `static FOO: Type = FOO;` causes a cycle error + // instead of magically pulling *any* ZST value from the ether, we need to + // trigger a read here. + self.get_raw(ptr.alloc_id)?; + None + } else { + Some(ptr) + } } }) } diff --git a/src/test/ui/consts/recursive-zst-static.rs b/src/test/ui/consts/recursive-zst-static.rs index df7562bd9f5d2..768df58e1e32e 100644 --- a/src/test/ui/consts/recursive-zst-static.rs +++ b/src/test/ui/consts/recursive-zst-static.rs @@ -1,6 +1,10 @@ -// build-pass +// This test ensures that we do not allow ZST statics to initialize themselves without ever +// actually creating a value of that type. This is important, as the ZST may have private fields +// that users can reasonably expect to only get initialized by their own code. Thus unsafe code +// can depend on this fact and will thus do unsound things when it is violated. +// See https://github.com/rust-lang/rust/issues/71078 for more details. -static FOO: () = FOO; +static FOO: () = FOO; //~ cycle detected when const-evaluating `FOO` fn main() { FOO diff --git a/src/test/ui/consts/recursive-zst-static.stderr b/src/test/ui/consts/recursive-zst-static.stderr new file mode 100644 index 0000000000000..e21dcf691ab0a --- /dev/null +++ b/src/test/ui/consts/recursive-zst-static.stderr @@ -0,0 +1,21 @@ +error[E0391]: cycle detected when const-evaluating `FOO` + --> $DIR/recursive-zst-static.rs:7:18 + | +LL | static FOO: () = FOO; + | ^^^ + | +note: ...which requires const-evaluating `FOO`... + --> $DIR/recursive-zst-static.rs:7:1 + | +LL | static FOO: () = FOO; + | ^^^^^^^^^^^^^^^^^^^^^ + = note: ...which again requires const-evaluating `FOO`, completing the cycle +note: cycle used when const-evaluating + checking `FOO` + --> $DIR/recursive-zst-static.rs:7:1 + | +LL | static FOO: () = FOO; + | ^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0391`.