ICE: build cache corruption

[elinorbgr]

Sorry, the testcase is not exactly simple, but:

• checkout this repository on this commit : https://github.com/Smithay/wayland-rs/tree/02e81d6893c90f4ebfa93c70991fa3ab1fd12ff7
• cargo +beta test --all --all-features
• apply the following diff to the repository

diff --git a/wayland-server/src/lib.rs b/wayland-server/src/lib.rs
index 8685ab04..f83909dd 100644
--- a/wayland-server/src/lib.rs
+++ b/wayland-server/src/lib.rs
@@ -1,3 +1,5 @@
+#![warn(missing_docs)]
+
 #[macro_use]
 extern crate bitflags;
 extern crate libc;

• re-run cargo +beta test --all --all-features
• ICE :

error: internal compiler error: librustc/ty/context.rs:998: tried to cache DefId(20/0:393 ~ wayland_server[52b1]::generated[0]::c_interfaces[0]::wl_surface_interface[0]), but was already existing as AllocId(
    451
)

• run cargo clean
• re-run cargo +beta test --all --all-features
• builds and run fine

$ rustc +beta --version
rustc 1.26.0-beta.1 (18aaa1d2c 2018-04-03)
$cargo +beta --version
cargo 1.26.0-beta (d63299b6e 2018-03-28)

Does not reproduce on stable 1.25, reproduces on nightly as well.

[oli-obk]

Do you have a generated Wayland_c_interfaces.rs at hand? If not I'll have a look tomorrow

[elinorbgr]

Here is one : https://gist.github.com/vberger/8ba4f91eefada94033efb8bc3f7b945c

[nikomatsakis]

triage: P-high

Regression, @oli-obk is on it.

[oli-obk]

I don't have a minimal repro yet, but it looks very much like this is only happening cross crate.

[oli-obk]

Minimized (probably not minimal) repro:

// a.rs
pub const FOO: *const i8 = 0 as *const i8;

pub static mut BAR: [*const i8; 4] = [FOO, FOO, FOO, FOO];

pub static mut BAA: (*const i8, i32, *const i8) = (
    unsafe { &BAR as *const _ as *const i8 },
    42,
    unsafe { &BOO as *const _ as *const i8 },
);
pub static mut BOO: (*const i8, *const i8, u32) = (
    unsafe { &BAA as *const _ as *const i8 },
    &FOO as *const _ as *const i8,
    99,
);

// b.rs
extern crate a;

static mut BOO: *const i32 = unsafe { &a::BOO as *const _ as *const i32 };

fn main() {}

Adding an empty line to the beginning of a.rs causes another symptom of this bug.

[oli-obk]

Fully minimized

pub static mut BAA: *const i8 = unsafe { &BOO as *const _ as *const i8 };
pub static mut BOO: *const i8 = unsafe { &BAA as *const _ as *const i8 };
fn main() {}

Adding an empty line to the beginning of the file causes an ICE.

The only possible fix I see is to add the previously discussed interpret-alloc-table that'll get cached via the footer instead of trying to do everything inline