Fix const evaluation ICE in rustdoc

[GuillaumeGomez]

Fixes #47860.

r? @eddyb

[eddyb]

@bors r+

[bors]

📌 Commit c786dca has been approved by eddyb

[ollie27]

The same issue exists when cross crate inlining:

rust/src/librustdoc/clean/mod.rs

Line 2580 in 90eb44a

n = cx.tcx.const_eval(param_env.and((def_id, substs))).unwrap()

[eddyb]

@ollie27 Oh, right. That would have to show "<error>" or similar.

[ollie27]

Would changing that line to this not work?

if let Ok(new_n) = cx.tcx.const_eval(param_env.and((def_id, substs))) {
    n = new_n;
}

[eddyb]

Oh oops sorry you're right!

@bors r-

[GuillaumeGomez]

Updated.

[eddyb]

Can you use the same trick in the other function? You just have to do this first, before const_eval:

let n = tcx.mk_const(ty::Const {
    val: ConstVal::Unevaluated(def_id, substs),
    ty: tcx.types.usize
});

[GuillaumeGomez]

Do you mean instead of const_eval? Otherwise, this new assignement to n will never be used...

[eddyb]

I mean it'd be this in the other place (line 2450) - rewrote it a bit since previous comment:

let n = cx.tcx.const_eval(param_env.and((def_id, substs))).unwrap_or_else(|_| {
    cx.tcx.mk_const(ty::Const {
        val: ConstVal::Unevaluated(def_id, substs),
        ty: cx.tcx.types.usize
    })
});

[GuillaumeGomez]

Updated.

[eddyb]

@bors r+

[bors]

📌 Commit 6b35d81 has been approved by eddyb

[bors]

⌛ Testing commit 6b35d81 with merge edecd1a5251488e5b7001ad0eee516738f648149...

[bors]

💔 Test failed - status-appveyor

[kennytm]

@bors retry #46903

[bors]

⌛ Testing commit 6b35d81 with merge e7e982a...

[bors]

💥 Test timed out

[kennytm]

@bors clean r- retry

(This PR was stuck in the queue as "failure" state.)